OpenCloudOS-Kernel/mm/gup.c

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// SPDX-License-Identifier: GPL-2.0-only
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/spinlock.h>
#include <linux/mm.h>
#include <linux/memremap.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
mm: introduce memfd_secret system call to create "secret" memory areas Introduce "memfd_secret" system call with the ability to create memory areas visible only in the context of the owning process and not mapped not only to other processes but in the kernel page tables as well. The secretmem feature is off by default and the user must explicitly enable it at the boot time. Once secretmem is enabled, the user will be able to create a file descriptor using the memfd_secret() system call. The memory areas created by mmap() calls from this file descriptor will be unmapped from the kernel direct map and they will be only mapped in the page table of the processes that have access to the file descriptor. Secretmem is designed to provide the following protections: * Enhanced protection (in conjunction with all the other in-kernel attack prevention systems) against ROP attacks. Seceretmem makes "simple" ROP insufficient to perform exfiltration, which increases the required complexity of the attack. Along with other protections like the kernel stack size limit and address space layout randomization which make finding gadgets is really hard, absence of any in-kernel primitive for accessing secret memory means the one gadget ROP attack can't work. Since the only way to access secret memory is to reconstruct the missing mapping entry, the attacker has to recover the physical page and insert a PTE pointing to it in the kernel and then retrieve the contents. That takes at least three gadgets which is a level of difficulty beyond most standard attacks. * Prevent cross-process secret userspace memory exposures. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere. The secreremem pages cannot be accessed via the direct map and they are disallowed in GUP. * Harden against exploited kernel flaws. In order to access secretmem, a kernel-side attack would need to either walk the page tables and create new ones, or spawn a new privileged uiserspace process to perform secrets exfiltration using ptrace. The file descriptor based memory has several advantages over the "traditional" mm interfaces, such as mlock(), mprotect(), madvise(). File descriptor approach allows explicit and controlled sharing of the memory areas, it allows to seal the operations. Besides, file descriptor based memory paves the way for VMMs to remove the secret memory range from the userspace hipervisor process, for instance QEMU. Andy Lutomirski says: "Getting fd-backed memory into a guest will take some possibly major work in the kernel, but getting vma-backed memory into a guest without mapping it in the host user address space seems much, much worse." memfd_secret() is made a dedicated system call rather than an extension to memfd_create() because it's purpose is to allow the user to create more secure memory mappings rather than to simply allow file based access to the memory. Nowadays a new system call cost is negligible while it is way simpler for userspace to deal with a clear-cut system calls than with a multiplexer or an overloaded syscall. Moreover, the initial implementation of memfd_secret() is completely distinct from memfd_create() so there is no much sense in overloading memfd_create() to begin with. If there will be a need for code sharing between these implementation it can be easily achieved without a need to adjust user visible APIs. The secret memory remains accessible in the process context using uaccess primitives, but it is not exposed to the kernel otherwise; secret memory areas are removed from the direct map and functions in the follow_page()/get_user_page() family will refuse to return a page that belongs to the secret memory area. Once there will be a use case that will require exposing secretmem to the kernel it will be an opt-in request in the system call flags so that user would have to decide what data can be exposed to the kernel. Removing of the pages from the direct map may cause its fragmentation on architectures that use large pages to map the physical memory which affects the system performance. However, the original Kconfig text for CONFIG_DIRECT_GBPAGES said that gigabyte pages in the direct map "... can improve the kernel's performance a tiny bit ..." (commit 00d1c5e05736 ("x86: add gbpages switches")) and the recent report [1] showed that "... although 1G mappings are a good default choice, there is no compelling evidence that it must be the only choice". Hence, it is sufficient to have secretmem disabled by default with the ability of a system administrator to enable it at boot time. Pages in the secretmem regions are unevictable and unmovable to avoid accidental exposure of the sensitive data via swap or during page migration. Since the secretmem mappings are locked in memory they cannot exceed RLIMIT_MEMLOCK. Since these mappings are already locked independently from mlock(), an attempt to mlock()/munlock() secretmem range would fail and mlockall()/munlockall() will ignore secretmem mappings. However, unlike mlock()ed memory, secretmem currently behaves more like long-term GUP: secretmem mappings are unmovable mappings directly consumed by user space. With default limits, there is no excessive use of secretmem and it poses no real problem in combination with ZONE_MOVABLE/CMA, but in the future this should be addressed to allow balanced use of large amounts of secretmem along with ZONE_MOVABLE/CMA. A page that was a part of the secret memory area is cleared when it is freed to ensure the data is not exposed to the next user of that page. The following example demonstrates creation of a secret mapping (error handling is omitted): fd = memfd_secret(0); ftruncate(fd, MAP_SIZE); ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); [1] https://lore.kernel.org/linux-mm/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux.intel.com/ [akpm@linux-foundation.org: suppress Kconfig whine] Link: https://lkml.kernel.org/r/20210518072034.31572-5-rppt@kernel.org Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: Hagen Paul Pfeifer <hagen@jauu.net> Acked-by: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christopher Lameter <cl@linux.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Bottomley <jejb@linux.ibm.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Palmer Dabbelt <palmerdabbelt@google.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tycho Andersen <tycho@tycho.ws> Cc: Will Deacon <will@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: kernel test robot <lkp@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-08 09:08:03 +08:00
#include <linux/secretmem.h>
#include <linux/sched/signal.h>
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
#include <linux/rwsem.h>
#include <linux/hugetlb.h>
#include <linux/migrate.h>
#include <linux/mm_inline.h>
#include <linux/sched/mm.h>
mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys Today, for normal faults and page table walks, we check the VMA and/or PTE to ensure that it is compatible with the action. For instance, if we get a write fault on a non-writeable VMA, we SIGSEGV. We try to do the same thing for protection keys. Basically, we try to make sure that if a user does this: mprotect(ptr, size, PROT_NONE); *ptr = foo; they see the same effects with protection keys when they do this: mprotect(ptr, size, PROT_READ|PROT_WRITE); set_pkey(ptr, size, 4); wrpkru(0xffffff3f); // access disable pkey 4 *ptr = foo; The state to do that checking is in the VMA, but we also sometimes have to do it on the page tables only, like when doing a get_user_pages_fast() where we have no VMA. We add two functions and expose them to generic code: arch_pte_access_permitted(pte_flags, write) arch_vma_access_permitted(vma, write) These are, of course, backed up in x86 arch code with checks against the PTE or VMA's protection key. But, there are also cases where we do not want to respect protection keys. When we ptrace(), for instance, we do not want to apply the tracer's PKRU permissions to the PTEs from the process being traced. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave@sr71.net> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: David Hildenbrand <dahi@linux.vnet.ibm.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20160212210219.14D5D715@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:19 +08:00
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
#include "internal.h"
struct follow_page_context {
struct dev_pagemap *pgmap;
unsigned int page_mask;
};
mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Let's verify when (un)pinning anonymous pages that we always deal with exclusive anonymous pages, which guarantees that we'll have a reliable PIN, meaning that we cannot end up with the GUP pin being inconsistent with he pages mapped into the page tables due to a COW triggered by a write fault. When pinning pages, after conditionally triggering GUP unsharing of possibly shared anonymous pages, we should always only see exclusive anonymous pages. Note that anonymous pages that are mapped writable must be marked exclusive, otherwise we'd have a BUG. When pinning during ordinary GUP, simply add a check after our conditional GUP-triggered unsharing checks. As we know exactly how the page is mapped, we know exactly in which page we have to check for PageAnonExclusive(). When pinning via GUP-fast we have to be careful, because we can race with fork(): verify only after we made sure via the seqcount that we didn't race with concurrent fork() that we didn't end up pinning a possibly shared anonymous page. Similarly, when unpinning, verify that the pages are still marked as exclusive: otherwise something turned the pages possibly shared, which can result in random memory corruptions, which we really want to catch. With only the pinned pages at hand and not the actual page table entries we have to be a bit careful: hugetlb pages are always mapped via a single logical page table entry referencing the head page and PG_anon_exclusive of the head page applies. Anon THP are a bit more complicated, because we might have obtained the page reference either via a PMD or a PTE -- depending on the mapping type we either have to check PageAnonExclusive of the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies: as we don't know and to make our life easier, check that either is set. Take care to not verify in case we're unpinning during GUP-fast because we detected concurrent fork(): we might stumble over an anonymous page that is now shared. Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
static inline void sanity_check_pinned_pages(struct page **pages,
unsigned long npages)
{
if (!IS_ENABLED(CONFIG_DEBUG_VM))
return;
/*
* We only pin anonymous pages if they are exclusive. Once pinned, we
* can no longer turn them possibly shared and PageAnonExclusive() will
* stick around until the page is freed.
*
* We'd like to verify that our pinned anonymous pages are still mapped
* exclusively. The issue with anon THP is that we don't know how
* they are/were mapped when pinning them. However, for anon
* THP we can assume that either the given page (PTE-mapped THP) or
* the head page (PMD-mapped THP) should be PageAnonExclusive(). If
* neither is the case, there is certainly something wrong.
*/
for (; npages; npages--, pages++) {
struct page *page = *pages;
struct folio *folio = page_folio(page);
if (!folio_test_anon(folio))
continue;
if (!folio_test_large(folio) || folio_test_hugetlb(folio))
VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page), page);
else
/* Either a PTE-mapped or a PMD-mapped THP. */
VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page) &&
!PageAnonExclusive(page), page);
}
}
Revert "mm/gup: remove try_get_page(), call try_get_compound_head() directly" This reverts commit 9857a17f206ff374aea78bccfb687f145368be2e. That commit was completely broken, and I should have caught on to it earlier. But happily, the kernel test robot noticed the breakage fairly quickly. The breakage is because "try_get_page()" is about avoiding the page reference count overflow case, but is otherwise the exact same as a plain "get_page()". In contrast, "try_get_compound_head()" is an entirely different beast, and uses __page_cache_add_speculative() because it's not just about the page reference count, but also about possibly racing with the underlying page going away. So all the commentary about how "try_get_page() has fallen a little behind in terms of maintenance, try_get_compound_head() handles speculative page references more thoroughly" was just completely wrong: yes, try_get_compound_head() handles speculative page references, but the point is that try_get_page() does not, and must not. So there's no lack of maintainance - there are fundamentally different semantics. A speculative page reference would be entirely wrong in "get_page()", and it's entirely wrong in "try_get_page()". It's not about speculation, it's purely about "uhhuh, you can't get this page because you've tried to increment the reference count too much already". The reason the kernel test robot noticed this bug was that it hit the VM_BUG_ON() in __page_cache_add_speculative(), which is all about verifying that the context of any speculative page access is correct. But since that isn't what try_get_page() is all about, the VM_BUG_ON() tests things that are not correct to test for try_get_page(). Reported-by: kernel test robot <oliver.sang@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-09-08 02:03:45 +08:00
/*
* Return the folio with ref appropriately incremented,
Revert "mm/gup: remove try_get_page(), call try_get_compound_head() directly" This reverts commit 9857a17f206ff374aea78bccfb687f145368be2e. That commit was completely broken, and I should have caught on to it earlier. But happily, the kernel test robot noticed the breakage fairly quickly. The breakage is because "try_get_page()" is about avoiding the page reference count overflow case, but is otherwise the exact same as a plain "get_page()". In contrast, "try_get_compound_head()" is an entirely different beast, and uses __page_cache_add_speculative() because it's not just about the page reference count, but also about possibly racing with the underlying page going away. So all the commentary about how "try_get_page() has fallen a little behind in terms of maintenance, try_get_compound_head() handles speculative page references more thoroughly" was just completely wrong: yes, try_get_compound_head() handles speculative page references, but the point is that try_get_page() does not, and must not. So there's no lack of maintainance - there are fundamentally different semantics. A speculative page reference would be entirely wrong in "get_page()", and it's entirely wrong in "try_get_page()". It's not about speculation, it's purely about "uhhuh, you can't get this page because you've tried to increment the reference count too much already". The reason the kernel test robot noticed this bug was that it hit the VM_BUG_ON() in __page_cache_add_speculative(), which is all about verifying that the context of any speculative page access is correct. But since that isn't what try_get_page() is all about, the VM_BUG_ON() tests things that are not correct to test for try_get_page(). Reported-by: kernel test robot <oliver.sang@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-09-08 02:03:45 +08:00
* or NULL if that failed.
*/
static inline struct folio *try_get_folio(struct page *page, int refs)
{
struct folio *folio;
retry:
folio = page_folio(page);
if (WARN_ON_ONCE(folio_ref_count(folio) < 0))
return NULL;
if (unlikely(!folio_ref_try_add_rcu(folio, refs)))
return NULL;
mm/gup: fix try_grab_compound_head() race with split_huge_page() try_grab_compound_head() is used to grab a reference to a page from get_user_pages_fast(), which is only protected against concurrent freeing of page tables (via local_irq_save()), but not against concurrent TLB flushes, freeing of data pages, or splitting of compound pages. Because no reference is held to the page when try_grab_compound_head() is called, the page may have been freed and reallocated by the time its refcount has been elevated; therefore, once we're holding a stable reference to the page, the caller re-checks whether the PTE still points to the same page (with the same access rights). The problem is that try_grab_compound_head() has to grab a reference on the head page; but between the time we look up what the head page is and the time we actually grab a reference on the head page, the compound page may have been split up (either explicitly through split_huge_page() or by freeing the compound page to the buddy allocator and then allocating its individual order-0 pages). If that happens, get_user_pages_fast() may end up returning the right page but lifting the refcount on a now-unrelated page, leading to use-after-free of pages. To fix it: Re-check whether the pages still belong together after lifting the refcount on the head page. Move anything else that checks compound_head(page) below the refcount increment. This can't actually happen on bare-metal x86 (because there, disabling IRQs locks out remote TLB flushes), but it can happen on virtualized x86 (e.g. under KVM) and probably also on arm64. The race window is pretty narrow, and constantly allocating and shattering hugepages isn't exactly fast; for now I've only managed to reproduce this in an x86 KVM guest with an artificially widened timing window (by adding a loop that repeatedly calls `inl(0x3f8 + 5)` in `try_get_compound_head()` to force VM exits, so that PV TLB flushes are used instead of IPIs). As requested on the list, also replace the existing VM_BUG_ON_PAGE() with a warning and bailout. Since the existing code only performed the BUG_ON check on DEBUG_VM kernels, ensure that the new code also only performs the check under that configuration - I don't want to mix two logically separate changes together too much. The macro VM_WARN_ON_ONCE_PAGE() doesn't return a value on !DEBUG_VM, so wrap the whole check in an #ifdef block. An alternative would be to change the VM_WARN_ON_ONCE_PAGE() definition for !DEBUG_VM such that it always returns false, but since that would differ from the behavior of the normal WARN macros, it might be too confusing for readers. Link: https://lkml.kernel.org/r/20210615012014.1100672-1-jannh@google.com Fixes: 7aef4172c795 ("mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton") Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Jan Kara <jack@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:33:23 +08:00
/*
* At this point we have a stable reference to the folio; but it
* could be that between calling page_folio() and the refcount
* increment, the folio was split, in which case we'd end up
* holding a reference on a folio that has nothing to do with the page
mm/gup: fix try_grab_compound_head() race with split_huge_page() try_grab_compound_head() is used to grab a reference to a page from get_user_pages_fast(), which is only protected against concurrent freeing of page tables (via local_irq_save()), but not against concurrent TLB flushes, freeing of data pages, or splitting of compound pages. Because no reference is held to the page when try_grab_compound_head() is called, the page may have been freed and reallocated by the time its refcount has been elevated; therefore, once we're holding a stable reference to the page, the caller re-checks whether the PTE still points to the same page (with the same access rights). The problem is that try_grab_compound_head() has to grab a reference on the head page; but between the time we look up what the head page is and the time we actually grab a reference on the head page, the compound page may have been split up (either explicitly through split_huge_page() or by freeing the compound page to the buddy allocator and then allocating its individual order-0 pages). If that happens, get_user_pages_fast() may end up returning the right page but lifting the refcount on a now-unrelated page, leading to use-after-free of pages. To fix it: Re-check whether the pages still belong together after lifting the refcount on the head page. Move anything else that checks compound_head(page) below the refcount increment. This can't actually happen on bare-metal x86 (because there, disabling IRQs locks out remote TLB flushes), but it can happen on virtualized x86 (e.g. under KVM) and probably also on arm64. The race window is pretty narrow, and constantly allocating and shattering hugepages isn't exactly fast; for now I've only managed to reproduce this in an x86 KVM guest with an artificially widened timing window (by adding a loop that repeatedly calls `inl(0x3f8 + 5)` in `try_get_compound_head()` to force VM exits, so that PV TLB flushes are used instead of IPIs). As requested on the list, also replace the existing VM_BUG_ON_PAGE() with a warning and bailout. Since the existing code only performed the BUG_ON check on DEBUG_VM kernels, ensure that the new code also only performs the check under that configuration - I don't want to mix two logically separate changes together too much. The macro VM_WARN_ON_ONCE_PAGE() doesn't return a value on !DEBUG_VM, so wrap the whole check in an #ifdef block. An alternative would be to change the VM_WARN_ON_ONCE_PAGE() definition for !DEBUG_VM such that it always returns false, but since that would differ from the behavior of the normal WARN macros, it might be too confusing for readers. Link: https://lkml.kernel.org/r/20210615012014.1100672-1-jannh@google.com Fixes: 7aef4172c795 ("mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton") Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Jan Kara <jack@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:33:23 +08:00
* we were given anymore.
* So now that the folio is stable, recheck that the page still
* belongs to this folio.
mm/gup: fix try_grab_compound_head() race with split_huge_page() try_grab_compound_head() is used to grab a reference to a page from get_user_pages_fast(), which is only protected against concurrent freeing of page tables (via local_irq_save()), but not against concurrent TLB flushes, freeing of data pages, or splitting of compound pages. Because no reference is held to the page when try_grab_compound_head() is called, the page may have been freed and reallocated by the time its refcount has been elevated; therefore, once we're holding a stable reference to the page, the caller re-checks whether the PTE still points to the same page (with the same access rights). The problem is that try_grab_compound_head() has to grab a reference on the head page; but between the time we look up what the head page is and the time we actually grab a reference on the head page, the compound page may have been split up (either explicitly through split_huge_page() or by freeing the compound page to the buddy allocator and then allocating its individual order-0 pages). If that happens, get_user_pages_fast() may end up returning the right page but lifting the refcount on a now-unrelated page, leading to use-after-free of pages. To fix it: Re-check whether the pages still belong together after lifting the refcount on the head page. Move anything else that checks compound_head(page) below the refcount increment. This can't actually happen on bare-metal x86 (because there, disabling IRQs locks out remote TLB flushes), but it can happen on virtualized x86 (e.g. under KVM) and probably also on arm64. The race window is pretty narrow, and constantly allocating and shattering hugepages isn't exactly fast; for now I've only managed to reproduce this in an x86 KVM guest with an artificially widened timing window (by adding a loop that repeatedly calls `inl(0x3f8 + 5)` in `try_get_compound_head()` to force VM exits, so that PV TLB flushes are used instead of IPIs). As requested on the list, also replace the existing VM_BUG_ON_PAGE() with a warning and bailout. Since the existing code only performed the BUG_ON check on DEBUG_VM kernels, ensure that the new code also only performs the check under that configuration - I don't want to mix two logically separate changes together too much. The macro VM_WARN_ON_ONCE_PAGE() doesn't return a value on !DEBUG_VM, so wrap the whole check in an #ifdef block. An alternative would be to change the VM_WARN_ON_ONCE_PAGE() definition for !DEBUG_VM such that it always returns false, but since that would differ from the behavior of the normal WARN macros, it might be too confusing for readers. Link: https://lkml.kernel.org/r/20210615012014.1100672-1-jannh@google.com Fixes: 7aef4172c795 ("mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton") Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Jan Kara <jack@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:33:23 +08:00
*/
if (unlikely(page_folio(page) != folio)) {
if (!put_devmap_managed_page_refs(&folio->page, refs))
folio_put_refs(folio, refs);
goto retry;
mm/gup: fix try_grab_compound_head() race with split_huge_page() try_grab_compound_head() is used to grab a reference to a page from get_user_pages_fast(), which is only protected against concurrent freeing of page tables (via local_irq_save()), but not against concurrent TLB flushes, freeing of data pages, or splitting of compound pages. Because no reference is held to the page when try_grab_compound_head() is called, the page may have been freed and reallocated by the time its refcount has been elevated; therefore, once we're holding a stable reference to the page, the caller re-checks whether the PTE still points to the same page (with the same access rights). The problem is that try_grab_compound_head() has to grab a reference on the head page; but between the time we look up what the head page is and the time we actually grab a reference on the head page, the compound page may have been split up (either explicitly through split_huge_page() or by freeing the compound page to the buddy allocator and then allocating its individual order-0 pages). If that happens, get_user_pages_fast() may end up returning the right page but lifting the refcount on a now-unrelated page, leading to use-after-free of pages. To fix it: Re-check whether the pages still belong together after lifting the refcount on the head page. Move anything else that checks compound_head(page) below the refcount increment. This can't actually happen on bare-metal x86 (because there, disabling IRQs locks out remote TLB flushes), but it can happen on virtualized x86 (e.g. under KVM) and probably also on arm64. The race window is pretty narrow, and constantly allocating and shattering hugepages isn't exactly fast; for now I've only managed to reproduce this in an x86 KVM guest with an artificially widened timing window (by adding a loop that repeatedly calls `inl(0x3f8 + 5)` in `try_get_compound_head()` to force VM exits, so that PV TLB flushes are used instead of IPIs). As requested on the list, also replace the existing VM_BUG_ON_PAGE() with a warning and bailout. Since the existing code only performed the BUG_ON check on DEBUG_VM kernels, ensure that the new code also only performs the check under that configuration - I don't want to mix two logically separate changes together too much. The macro VM_WARN_ON_ONCE_PAGE() doesn't return a value on !DEBUG_VM, so wrap the whole check in an #ifdef block. An alternative would be to change the VM_WARN_ON_ONCE_PAGE() definition for !DEBUG_VM such that it always returns false, but since that would differ from the behavior of the normal WARN macros, it might be too confusing for readers. Link: https://lkml.kernel.org/r/20210615012014.1100672-1-jannh@google.com Fixes: 7aef4172c795 ("mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton") Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Jan Kara <jack@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:33:23 +08:00
}
return folio;
}
/**
* try_grab_folio() - Attempt to get or pin a folio.
* @page: pointer to page to be grabbed
* @refs: the value to (effectively) add to the folio's refcount
* @flags: gup flags: these are the FOLL_* flag values.
*
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
* "grab" names in this file mean, "look at flags to decide whether to use
* FOLL_PIN or FOLL_GET behavior, when incrementing the folio's refcount.
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
*
* Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at the
* same time. (That's true throughout the get_user_pages*() and
* pin_user_pages*() APIs.) Cases:
*
* FOLL_GET: folio's refcount will be incremented by @refs.
*
* FOLL_PIN on large folios: folio's refcount will be incremented by
* @refs, and its pincount will be incremented by @refs.
*
* FOLL_PIN on single-page folios: folio's refcount will be incremented by
* @refs * GUP_PIN_COUNTING_BIAS.
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
*
* Return: The folio containing @page (with refcount appropriately
* incremented) for success, or NULL upon failure. If neither FOLL_GET
* nor FOLL_PIN was set, that's considered failure, and furthermore,
* a likely bug in the caller, so a warning is also emitted.
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
*/
struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
{
if (unlikely(!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)))
return NULL;
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
if (flags & FOLL_GET)
return try_get_folio(page, refs);
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
else if (flags & FOLL_PIN) {
struct folio *folio;
mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path FOLL_LONGTERM is a special case of FOLL_PIN. It suggests a pin which is going to be given to hardware and can't move. It would truncate CMA permanently and should be excluded. In gup slow path, where __gup_longterm_locked->check_and_migrate_cma_pages() handles FOLL_LONGTERM, but in fast path, there lacks such a check, which means a possible leak of CMA page to longterm pinned. Place a check in try_grab_compound_head() in the fast path to fix the leak, and if FOLL_LONGTERM happens on CMA, it will fall back to slow path to migrate the page. Some note about the check: Huge page's subpages have the same migrate type due to either allocation from a free_list[] or alloc_contig_range() with param MIGRATE_MOVABLE. So it is enough to check on a single subpage by is_migrate_cma_page(subpage) Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Shuah Khan <shuah@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Link: http://lkml.kernel.org/r/1584876733-17405-3-git-send-email-kernelfans@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:06:04 +08:00
/*
* Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a
* right zone, so fail and let the caller fall back to the slow
* path.
mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path FOLL_LONGTERM is a special case of FOLL_PIN. It suggests a pin which is going to be given to hardware and can't move. It would truncate CMA permanently and should be excluded. In gup slow path, where __gup_longterm_locked->check_and_migrate_cma_pages() handles FOLL_LONGTERM, but in fast path, there lacks such a check, which means a possible leak of CMA page to longterm pinned. Place a check in try_grab_compound_head() in the fast path to fix the leak, and if FOLL_LONGTERM happens on CMA, it will fall back to slow path to migrate the page. Some note about the check: Huge page's subpages have the same migrate type due to either allocation from a free_list[] or alloc_contig_range() with param MIGRATE_MOVABLE. So it is enough to check on a single subpage by is_migrate_cma_page(subpage) Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Shuah Khan <shuah@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Link: http://lkml.kernel.org/r/1584876733-17405-3-git-send-email-kernelfans@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:06:04 +08:00
*/
if (unlikely((flags & FOLL_LONGTERM) &&
mm: rename is_pinnable_page() to is_longterm_pinnable_page() Patch series "Add MEMORY_DEVICE_COHERENT for coherent device memory mapping", v9. This patch series introduces MEMORY_DEVICE_COHERENT, a type of memory owned by a device that can be mapped into CPU page tables like MEMORY_DEVICE_GENERIC and can also be migrated like MEMORY_DEVICE_PRIVATE. This patch series is mostly self-contained except for a few places where it needs to update other subsystems to handle the new memory type. System stability and performance are not affected according to our ongoing testing, including xfstests. How it works: The system BIOS advertises the GPU device memory (aka VRAM) as SPM (special purpose memory) in the UEFI system address map. The amdgpu driver registers the memory with devmap as MEMORY_DEVICE_COHERENT using devm_memremap_pages. The initial user for this hardware page migration capability is the Frontier supercomputer project. This functionality is not AMD-specific. We expect other GPU vendors to find this functionality useful, and possibly other hardware types in the future. Our test nodes in the lab are similar to the Frontier configuration, with .5 TB of system memory plus 256 GB of device memory split across 4 GPUs, all in a single coherent address space. Page migration is expected to improve application efficiency significantly. We will report empirical results as they become available. Coherent device type pages at gup are now migrated back to system memory if they are being pinned long-term (FOLL_LONGTERM). The reason is, that long-term pinning would interfere with the device memory manager owning the device-coherent pages (e.g. evictions in TTM). These series incorporate Alistair Popple patches to do this migration from pin_user_pages() calls. hmm_gup_test has been added to hmm-test to test different get user pages calls. This series includes handling of device-managed anonymous pages returned by vm_normal_pages. Although they behave like normal pages for purposes of mapping in CPU page tables and for COW, they do not support LRU lists, NUMA migration or THP. We also introduced a FOLL_LRU flag that adds the same behaviour to follow_page and related APIs, to allow callers to specify that they expect to put pages on an LRU list. This patch (of 14): is_pinnable_page() and folio_is_pinnable() are renamed to is_longterm_pinnable_page() and folio_is_longterm_pinnable() respectively. These functions are used in the FOLL_LONGTERM flag context. Link: https://lkml.kernel.org/r/20220715150521.18165-1-alex.sierra@amd.com Link: https://lkml.kernel.org/r/20220715150521.18165-2-alex.sierra@amd.com Signed-off-by: Alex Sierra <alex.sierra@amd.com> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Felix Kuehling <Felix.Kuehling@amd.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-15 23:05:08 +08:00
!is_longterm_pinnable_page(page)))
mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path FOLL_LONGTERM is a special case of FOLL_PIN. It suggests a pin which is going to be given to hardware and can't move. It would truncate CMA permanently and should be excluded. In gup slow path, where __gup_longterm_locked->check_and_migrate_cma_pages() handles FOLL_LONGTERM, but in fast path, there lacks such a check, which means a possible leak of CMA page to longterm pinned. Place a check in try_grab_compound_head() in the fast path to fix the leak, and if FOLL_LONGTERM happens on CMA, it will fall back to slow path to migrate the page. Some note about the check: Huge page's subpages have the same migrate type due to either allocation from a free_list[] or alloc_contig_range() with param MIGRATE_MOVABLE. So it is enough to check on a single subpage by is_migrate_cma_page(subpage) Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Shuah Khan <shuah@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Link: http://lkml.kernel.org/r/1584876733-17405-3-git-send-email-kernelfans@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:06:04 +08:00
return NULL;
mm/gup: fix try_grab_compound_head() race with split_huge_page() try_grab_compound_head() is used to grab a reference to a page from get_user_pages_fast(), which is only protected against concurrent freeing of page tables (via local_irq_save()), but not against concurrent TLB flushes, freeing of data pages, or splitting of compound pages. Because no reference is held to the page when try_grab_compound_head() is called, the page may have been freed and reallocated by the time its refcount has been elevated; therefore, once we're holding a stable reference to the page, the caller re-checks whether the PTE still points to the same page (with the same access rights). The problem is that try_grab_compound_head() has to grab a reference on the head page; but between the time we look up what the head page is and the time we actually grab a reference on the head page, the compound page may have been split up (either explicitly through split_huge_page() or by freeing the compound page to the buddy allocator and then allocating its individual order-0 pages). If that happens, get_user_pages_fast() may end up returning the right page but lifting the refcount on a now-unrelated page, leading to use-after-free of pages. To fix it: Re-check whether the pages still belong together after lifting the refcount on the head page. Move anything else that checks compound_head(page) below the refcount increment. This can't actually happen on bare-metal x86 (because there, disabling IRQs locks out remote TLB flushes), but it can happen on virtualized x86 (e.g. under KVM) and probably also on arm64. The race window is pretty narrow, and constantly allocating and shattering hugepages isn't exactly fast; for now I've only managed to reproduce this in an x86 KVM guest with an artificially widened timing window (by adding a loop that repeatedly calls `inl(0x3f8 + 5)` in `try_get_compound_head()` to force VM exits, so that PV TLB flushes are used instead of IPIs). As requested on the list, also replace the existing VM_BUG_ON_PAGE() with a warning and bailout. Since the existing code only performed the BUG_ON check on DEBUG_VM kernels, ensure that the new code also only performs the check under that configuration - I don't want to mix two logically separate changes together too much. The macro VM_WARN_ON_ONCE_PAGE() doesn't return a value on !DEBUG_VM, so wrap the whole check in an #ifdef block. An alternative would be to change the VM_WARN_ON_ONCE_PAGE() definition for !DEBUG_VM such that it always returns false, but since that would differ from the behavior of the normal WARN macros, it might be too confusing for readers. Link: https://lkml.kernel.org/r/20210615012014.1100672-1-jannh@google.com Fixes: 7aef4172c795 ("mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton") Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Jan Kara <jack@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:33:23 +08:00
/*
* CAUTION: Don't use compound_head() on the page before this
* point, the result won't be stable.
*/
folio = try_get_folio(page, refs);
if (!folio)
mm/gup: fix try_grab_compound_head() race with split_huge_page() try_grab_compound_head() is used to grab a reference to a page from get_user_pages_fast(), which is only protected against concurrent freeing of page tables (via local_irq_save()), but not against concurrent TLB flushes, freeing of data pages, or splitting of compound pages. Because no reference is held to the page when try_grab_compound_head() is called, the page may have been freed and reallocated by the time its refcount has been elevated; therefore, once we're holding a stable reference to the page, the caller re-checks whether the PTE still points to the same page (with the same access rights). The problem is that try_grab_compound_head() has to grab a reference on the head page; but between the time we look up what the head page is and the time we actually grab a reference on the head page, the compound page may have been split up (either explicitly through split_huge_page() or by freeing the compound page to the buddy allocator and then allocating its individual order-0 pages). If that happens, get_user_pages_fast() may end up returning the right page but lifting the refcount on a now-unrelated page, leading to use-after-free of pages. To fix it: Re-check whether the pages still belong together after lifting the refcount on the head page. Move anything else that checks compound_head(page) below the refcount increment. This can't actually happen on bare-metal x86 (because there, disabling IRQs locks out remote TLB flushes), but it can happen on virtualized x86 (e.g. under KVM) and probably also on arm64. The race window is pretty narrow, and constantly allocating and shattering hugepages isn't exactly fast; for now I've only managed to reproduce this in an x86 KVM guest with an artificially widened timing window (by adding a loop that repeatedly calls `inl(0x3f8 + 5)` in `try_get_compound_head()` to force VM exits, so that PV TLB flushes are used instead of IPIs). As requested on the list, also replace the existing VM_BUG_ON_PAGE() with a warning and bailout. Since the existing code only performed the BUG_ON check on DEBUG_VM kernels, ensure that the new code also only performs the check under that configuration - I don't want to mix two logically separate changes together too much. The macro VM_WARN_ON_ONCE_PAGE() doesn't return a value on !DEBUG_VM, so wrap the whole check in an #ifdef block. An alternative would be to change the VM_WARN_ON_ONCE_PAGE() definition for !DEBUG_VM such that it always returns false, but since that would differ from the behavior of the normal WARN macros, it might be too confusing for readers. Link: https://lkml.kernel.org/r/20210615012014.1100672-1-jannh@google.com Fixes: 7aef4172c795 ("mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton") Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Jan Kara <jack@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:33:23 +08:00
return NULL;
mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages For huge pages (and in fact, any compound page), the GUP_PIN_COUNTING_BIAS scheme tends to overflow too easily, each tail page increments the head page->_refcount by GUP_PIN_COUNTING_BIAS (1024). That limits the number of huge pages that can be pinned. This patch removes that limitation, by using an exact form of pin counting for compound pages of order > 1. The "order > 1" is required because this approach uses the 3rd struct page in the compound page, and order 1 compound pages only have two pages, so that won't work there. A new struct page field, hpage_pinned_refcount, has been added, replacing a padding field in the union (so no new space is used). This enhancement also has a useful side effect: huge pages and compound pages (of order > 1) do not suffer from the "potential false positives" problem that is discussed in the page_dma_pinned() comment block. That is because these compound pages have extra space for tracking things, so they get exact pin counts instead of overloading page->_refcount. Documentation/core-api/pin_user_pages.rst is updated accordingly. Suggested-by: Jan Kara <jack@suse.cz> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-8-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:33 +08:00
/*
* When pinning a large folio, use an exact count to track it.
mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages For huge pages (and in fact, any compound page), the GUP_PIN_COUNTING_BIAS scheme tends to overflow too easily, each tail page increments the head page->_refcount by GUP_PIN_COUNTING_BIAS (1024). That limits the number of huge pages that can be pinned. This patch removes that limitation, by using an exact form of pin counting for compound pages of order > 1. The "order > 1" is required because this approach uses the 3rd struct page in the compound page, and order 1 compound pages only have two pages, so that won't work there. A new struct page field, hpage_pinned_refcount, has been added, replacing a padding field in the union (so no new space is used). This enhancement also has a useful side effect: huge pages and compound pages (of order > 1) do not suffer from the "potential false positives" problem that is discussed in the page_dma_pinned() comment block. That is because these compound pages have extra space for tracking things, so they get exact pin counts instead of overloading page->_refcount. Documentation/core-api/pin_user_pages.rst is updated accordingly. Suggested-by: Jan Kara <jack@suse.cz> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-8-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:33 +08:00
*
* However, be sure to *also* increment the normal folio
* refcount field at least once, so that the folio really
* is pinned. That's why the refcount from the earlier
* try_get_folio() is left intact.
mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages For huge pages (and in fact, any compound page), the GUP_PIN_COUNTING_BIAS scheme tends to overflow too easily, each tail page increments the head page->_refcount by GUP_PIN_COUNTING_BIAS (1024). That limits the number of huge pages that can be pinned. This patch removes that limitation, by using an exact form of pin counting for compound pages of order > 1. The "order > 1" is required because this approach uses the 3rd struct page in the compound page, and order 1 compound pages only have two pages, so that won't work there. A new struct page field, hpage_pinned_refcount, has been added, replacing a padding field in the union (so no new space is used). This enhancement also has a useful side effect: huge pages and compound pages (of order > 1) do not suffer from the "potential false positives" problem that is discussed in the page_dma_pinned() comment block. That is because these compound pages have extra space for tracking things, so they get exact pin counts instead of overloading page->_refcount. Documentation/core-api/pin_user_pages.rst is updated accordingly. Suggested-by: Jan Kara <jack@suse.cz> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-8-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:33 +08:00
*/
if (folio_test_large(folio))
atomic_add(refs, &folio->_pincount);
mm/gup: fix try_grab_compound_head() race with split_huge_page() try_grab_compound_head() is used to grab a reference to a page from get_user_pages_fast(), which is only protected against concurrent freeing of page tables (via local_irq_save()), but not against concurrent TLB flushes, freeing of data pages, or splitting of compound pages. Because no reference is held to the page when try_grab_compound_head() is called, the page may have been freed and reallocated by the time its refcount has been elevated; therefore, once we're holding a stable reference to the page, the caller re-checks whether the PTE still points to the same page (with the same access rights). The problem is that try_grab_compound_head() has to grab a reference on the head page; but between the time we look up what the head page is and the time we actually grab a reference on the head page, the compound page may have been split up (either explicitly through split_huge_page() or by freeing the compound page to the buddy allocator and then allocating its individual order-0 pages). If that happens, get_user_pages_fast() may end up returning the right page but lifting the refcount on a now-unrelated page, leading to use-after-free of pages. To fix it: Re-check whether the pages still belong together after lifting the refcount on the head page. Move anything else that checks compound_head(page) below the refcount increment. This can't actually happen on bare-metal x86 (because there, disabling IRQs locks out remote TLB flushes), but it can happen on virtualized x86 (e.g. under KVM) and probably also on arm64. The race window is pretty narrow, and constantly allocating and shattering hugepages isn't exactly fast; for now I've only managed to reproduce this in an x86 KVM guest with an artificially widened timing window (by adding a loop that repeatedly calls `inl(0x3f8 + 5)` in `try_get_compound_head()` to force VM exits, so that PV TLB flushes are used instead of IPIs). As requested on the list, also replace the existing VM_BUG_ON_PAGE() with a warning and bailout. Since the existing code only performed the BUG_ON check on DEBUG_VM kernels, ensure that the new code also only performs the check under that configuration - I don't want to mix two logically separate changes together too much. The macro VM_WARN_ON_ONCE_PAGE() doesn't return a value on !DEBUG_VM, so wrap the whole check in an #ifdef block. An alternative would be to change the VM_WARN_ON_ONCE_PAGE() definition for !DEBUG_VM such that it always returns false, but since that would differ from the behavior of the normal WARN macros, it might be too confusing for readers. Link: https://lkml.kernel.org/r/20210615012014.1100672-1-jannh@google.com Fixes: 7aef4172c795 ("mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton") Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Jan Kara <jack@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:33:23 +08:00
else
folio_ref_add(folio,
refs * (GUP_PIN_COUNTING_BIAS - 1));
mm: fix PageAnonExclusive clearing racing with concurrent RCU GUP-fast commit 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive") made sure that when PageAnonExclusive() has to be cleared during temporary unmapping of a page, that the PTE is cleared/invalidated and that the TLB is flushed. What we want to achieve in all cases is that we cannot end up with a pin on an anonymous page that may be shared, because such pins would be unreliable and could result in memory corruptions when the mapped page and the pin go out of sync due to a write fault. That TLB flush handling was inspired by an outdated comment in mm/ksm.c:write_protect_page(), which similarly required the TLB flush in the past to synchronize with GUP-fast. However, ever since general RCU GUP fast was introduced in commit 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()"), a TLB flush is no longer sufficient to handle concurrent GUP-fast in all cases -- it only handles traditional IPI-based GUP-fast correctly. Peter Xu (thankfully) questioned whether that TLB flush is really required. On architectures that send an IPI broadcast on TLB flush, it works as expected. To synchronize with RCU GUP-fast properly, we're conceptually fine, however, we have to enforce a certain memory order and are missing memory barriers. Let's document that, avoid the TLB flush where possible and use proper explicit memory barriers where required. We shouldn't really care about the additional memory barriers here, as we're not on extremely hot paths -- and we're getting rid of some TLB flushes. We use a smp_mb() pair for handling concurrent pinning and a smp_rmb()/smp_wmb() pair for handling the corner case of only temporary PTE changes but permanent PageAnonExclusive changes. One extreme example, whereby GUP-fast takes a R/O pin and KSM wants to convert an exclusive anonymous page to a KSM page, and that page is already mapped write-protected (-> no PTE change) would be: Thread 0 (KSM) Thread 1 (GUP-fast) (B1) Read the PTE # (B2) skipped without FOLL_WRITE (A1) Clear PTE smp_mb() (A2) Check pinned (B3) Pin the mapped page smp_mb() (A3) Clear PageAnonExclusive smp_wmb() (A4) Restore PTE (B4) Check if the PTE changed smp_rmb() (B5) Check PageAnonExclusive Thread 1 will properly detect that PageAnonExclusive was cleared and back off. Note that we don't need a memory barrier between checking if the page is pinned and clearing PageAnonExclusive, because stores are not speculated. The possible issues due to reordering are of theoretical nature so far and attempts to reproduce the race failed. Especially the "no PTE change" case isn't the common case, because we'd need an exclusive anonymous page that's mapped R/O and the PTE is clean in KSM code -- and using KSM with page pinning isn't extremely common. Further, the clear+TLB flush we used for now implies a memory barrier. So the problematic missing part should be the missing memory barrier after pinning but before checking if the PTE changed. Link: https://lkml.kernel.org/r/20220901083559.67446-1-david@redhat.com Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive") Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Peter Xu <peterx@redhat.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Nadav Amit <namit@vmware.com> Cc: Yang Shi <shy828301@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Andrea Parri <parri.andrea@gmail.com> Cc: Will Deacon <will@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Christoph von Recklinghausen <crecklin@redhat.com> Cc: Don Dutile <ddutile@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-09-01 16:35:59 +08:00
/*
* Adjust the pincount before re-checking the PTE for changes.
* This is essentially a smp_mb() and is paired with a memory
* barrier in page_try_share_anon_rmap().
*/
smp_mb__after_atomic();
node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs);
mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages For huge pages (and in fact, any compound page), the GUP_PIN_COUNTING_BIAS scheme tends to overflow too easily, each tail page increments the head page->_refcount by GUP_PIN_COUNTING_BIAS (1024). That limits the number of huge pages that can be pinned. This patch removes that limitation, by using an exact form of pin counting for compound pages of order > 1. The "order > 1" is required because this approach uses the 3rd struct page in the compound page, and order 1 compound pages only have two pages, so that won't work there. A new struct page field, hpage_pinned_refcount, has been added, replacing a padding field in the union (so no new space is used). This enhancement also has a useful side effect: huge pages and compound pages (of order > 1) do not suffer from the "potential false positives" problem that is discussed in the page_dma_pinned() comment block. That is because these compound pages have extra space for tracking things, so they get exact pin counts instead of overloading page->_refcount. Documentation/core-api/pin_user_pages.rst is updated accordingly. Suggested-by: Jan Kara <jack@suse.cz> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-8-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:33 +08:00
return folio;
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
}
WARN_ON_ONCE(1);
return NULL;
}
static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
mm/gup: combine put_compound_head() and unpin_user_page() These functions accomplish the same thing but have different implementations. unpin_user_page() has a bug where it calls mod_node_page_state() after calling put_page() which creates a risk that the page could have been hot-uplugged from the system. Fix this by using put_compound_head() as the only implementation. __unpin_devmap_managed_user_page() and related can be deleted as well in favour of the simpler, but slower, version in put_compound_head() that has an extra atomic page_ref_sub, but always calls put_page() which internally contains the special devmap code. Move put_compound_head() to be directly after try_grab_compound_head() so people can find it in future. Link: https://lkml.kernel.org/r/0-v1-6730d4ee0d32+40e6-gup_combine_put_jgg@nvidia.com Fixes: 1970dc6f5226 ("mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting") Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jan Kara <jack@suse.cz> CC: Joao Martins <joao.m.martins@oracle.com> CC: Jonathan Corbet <corbet@lwn.net> CC: Dan Williams <dan.j.williams@intel.com> CC: Dave Chinner <david@fromorbit.com> CC: Christoph Hellwig <hch@infradead.org> CC: Jane Chu <jane.chu@oracle.com> CC: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> CC: Michal Hocko <mhocko@suse.com> CC: Mike Kravetz <mike.kravetz@oracle.com> CC: Shuah Khan <shuah@kernel.org> CC: Muchun Song <songmuchun@bytedance.com> CC: Vlastimil Babka <vbabka@suse.cz> CC: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:51 +08:00
{
if (flags & FOLL_PIN) {
node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs);
if (folio_test_large(folio))
atomic_sub(refs, &folio->_pincount);
mm/gup: combine put_compound_head() and unpin_user_page() These functions accomplish the same thing but have different implementations. unpin_user_page() has a bug where it calls mod_node_page_state() after calling put_page() which creates a risk that the page could have been hot-uplugged from the system. Fix this by using put_compound_head() as the only implementation. __unpin_devmap_managed_user_page() and related can be deleted as well in favour of the simpler, but slower, version in put_compound_head() that has an extra atomic page_ref_sub, but always calls put_page() which internally contains the special devmap code. Move put_compound_head() to be directly after try_grab_compound_head() so people can find it in future. Link: https://lkml.kernel.org/r/0-v1-6730d4ee0d32+40e6-gup_combine_put_jgg@nvidia.com Fixes: 1970dc6f5226 ("mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting") Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jan Kara <jack@suse.cz> CC: Joao Martins <joao.m.martins@oracle.com> CC: Jonathan Corbet <corbet@lwn.net> CC: Dan Williams <dan.j.williams@intel.com> CC: Dave Chinner <david@fromorbit.com> CC: Christoph Hellwig <hch@infradead.org> CC: Jane Chu <jane.chu@oracle.com> CC: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> CC: Michal Hocko <mhocko@suse.com> CC: Mike Kravetz <mike.kravetz@oracle.com> CC: Shuah Khan <shuah@kernel.org> CC: Muchun Song <songmuchun@bytedance.com> CC: Vlastimil Babka <vbabka@suse.cz> CC: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:51 +08:00
else
refs *= GUP_PIN_COUNTING_BIAS;
}
if (!put_devmap_managed_page_refs(&folio->page, refs))
folio_put_refs(folio, refs);
mm/gup: combine put_compound_head() and unpin_user_page() These functions accomplish the same thing but have different implementations. unpin_user_page() has a bug where it calls mod_node_page_state() after calling put_page() which creates a risk that the page could have been hot-uplugged from the system. Fix this by using put_compound_head() as the only implementation. __unpin_devmap_managed_user_page() and related can be deleted as well in favour of the simpler, but slower, version in put_compound_head() that has an extra atomic page_ref_sub, but always calls put_page() which internally contains the special devmap code. Move put_compound_head() to be directly after try_grab_compound_head() so people can find it in future. Link: https://lkml.kernel.org/r/0-v1-6730d4ee0d32+40e6-gup_combine_put_jgg@nvidia.com Fixes: 1970dc6f5226 ("mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting") Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jan Kara <jack@suse.cz> CC: Joao Martins <joao.m.martins@oracle.com> CC: Jonathan Corbet <corbet@lwn.net> CC: Dan Williams <dan.j.williams@intel.com> CC: Dave Chinner <david@fromorbit.com> CC: Christoph Hellwig <hch@infradead.org> CC: Jane Chu <jane.chu@oracle.com> CC: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> CC: Michal Hocko <mhocko@suse.com> CC: Mike Kravetz <mike.kravetz@oracle.com> CC: Shuah Khan <shuah@kernel.org> CC: Muchun Song <songmuchun@bytedance.com> CC: Vlastimil Babka <vbabka@suse.cz> CC: Matthew Wilcox <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:51 +08:00
}
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
/**
* try_grab_page() - elevate a page's refcount by a flag-dependent amount
* @page: pointer to page to be grabbed
* @flags: gup flags: these are the FOLL_* flag values.
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
*
* This might not do anything at all, depending on the flags argument.
*
* "grab" names in this file mean, "look at flags to decide whether to use
* FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
*
* Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
* time. Cases: please see the try_grab_folio() documentation, with
* "refs=1".
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
*
* Return: 0 for success, or if no action was required (if neither FOLL_PIN
* nor FOLL_GET was set, nothing is done). A negative error code for failure:
*
* -ENOMEM FOLL_GET or FOLL_PIN was set, but the page could not
* be grabbed.
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
*/
int __must_check try_grab_page(struct page *page, unsigned int flags)
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
{
struct folio *folio = page_folio(page);
if (WARN_ON_ONCE(folio_ref_count(folio) <= 0))
return -ENOMEM;
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
if (unlikely(!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)))
return -EREMOTEIO;
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
if (flags & FOLL_GET)
folio_ref_inc(folio);
else if (flags & FOLL_PIN) {
/*
* Similar to try_grab_folio(): be sure to *also*
* increment the normal page refcount field at least once,
* so that the page really is pinned.
*/
if (folio_test_large(folio)) {
folio_ref_add(folio, 1);
atomic_add(1, &folio->_pincount);
} else {
folio_ref_add(folio, GUP_PIN_COUNTING_BIAS);
}
node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1);
}
return 0;
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
}
/**
* unpin_user_page() - release a dma-pinned page
* @page: pointer to page to be released
*
* Pages that were pinned via pin_user_pages*() must be released via either
* unpin_user_page(), or one of the unpin_user_pages*() routines. This is so
* that such pages can be separately tracked and uniquely handled. In
* particular, interactions with RDMA and filesystems need special handling.
*/
void unpin_user_page(struct page *page)
{
mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Let's verify when (un)pinning anonymous pages that we always deal with exclusive anonymous pages, which guarantees that we'll have a reliable PIN, meaning that we cannot end up with the GUP pin being inconsistent with he pages mapped into the page tables due to a COW triggered by a write fault. When pinning pages, after conditionally triggering GUP unsharing of possibly shared anonymous pages, we should always only see exclusive anonymous pages. Note that anonymous pages that are mapped writable must be marked exclusive, otherwise we'd have a BUG. When pinning during ordinary GUP, simply add a check after our conditional GUP-triggered unsharing checks. As we know exactly how the page is mapped, we know exactly in which page we have to check for PageAnonExclusive(). When pinning via GUP-fast we have to be careful, because we can race with fork(): verify only after we made sure via the seqcount that we didn't race with concurrent fork() that we didn't end up pinning a possibly shared anonymous page. Similarly, when unpinning, verify that the pages are still marked as exclusive: otherwise something turned the pages possibly shared, which can result in random memory corruptions, which we really want to catch. With only the pinned pages at hand and not the actual page table entries we have to be a bit careful: hugetlb pages are always mapped via a single logical page table entry referencing the head page and PG_anon_exclusive of the head page applies. Anon THP are a bit more complicated, because we might have obtained the page reference either via a PMD or a PTE -- depending on the mapping type we either have to check PageAnonExclusive of the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies: as we don't know and to make our life easier, check that either is set. Take care to not verify in case we're unpinning during GUP-fast because we detected concurrent fork(): we might stumble over an anonymous page that is now shared. Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
sanity_check_pinned_pages(&page, 1);
gup_put_folio(page_folio(page), 1, FOLL_PIN);
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
}
EXPORT_SYMBOL(unpin_user_page);
static inline struct folio *gup_folio_range_next(struct page *start,
unsigned long npages, unsigned long i, unsigned int *ntails)
{
struct page *next = nth_page(start, i);
struct folio *folio = page_folio(next);
unsigned int nr = 1;
if (folio_test_large(folio))
nr = min_t(unsigned int, npages - i,
folio_nr_pages(folio) - folio_page_idx(folio, next));
*ntails = nr;
return folio;
}
static inline struct folio *gup_folio_next(struct page **list,
unsigned long npages, unsigned long i, unsigned int *ntails)
mm/gup: add compound page list iterator Patch series "mm/gup: page unpining improvements", v4. This series improves page unpinning, with an eye on improving MR deregistration for big swaths of memory (which is bound by the page unpining), particularly: 1) Decrement the head page by @ntails and thus reducing a lot the number of atomic operations per compound page. This is done by comparing individual tail pages heads, and counting number of consecutive tails on which they match heads and based on that update head page refcount. Should have a visible improvement in all page (un)pinners which use compound pages 2) Introducing a new API for unpinning page ranges (to avoid the trick in the previous item and be based on math), and use that in RDMA ib_mem_release (used for mr deregistration). Performance improvements: unpin_user_pages() for hugetlbfs and THP improves ~3x (through gup_test) and RDMA MR dereg improves ~4.5x with the new API. See patches 2 and 4 for those. This patch (of 4): Add a helper that iterates over head pages in a list of pages. It essentially counts the tails until the next page to process has a different head that the current. This is going to be used by unpin_user_pages() family of functions, to batch the head page refcount updates once for all passed consecutive tail pages. Link: https://lkml.kernel.org/r/20210212130843.13865-1-joao.m.martins@oracle.com Link: https://lkml.kernel.org/r/20210212130843.13865-2-joao.m.martins@oracle.com Signed-off-by: Joao Martins <joao.m.martins@oracle.com> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Cc: Doug Ledford <dledford@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 13:55:44 +08:00
{
struct folio *folio = page_folio(list[i]);
mm/gup: add compound page list iterator Patch series "mm/gup: page unpining improvements", v4. This series improves page unpinning, with an eye on improving MR deregistration for big swaths of memory (which is bound by the page unpining), particularly: 1) Decrement the head page by @ntails and thus reducing a lot the number of atomic operations per compound page. This is done by comparing individual tail pages heads, and counting number of consecutive tails on which they match heads and based on that update head page refcount. Should have a visible improvement in all page (un)pinners which use compound pages 2) Introducing a new API for unpinning page ranges (to avoid the trick in the previous item and be based on math), and use that in RDMA ib_mem_release (used for mr deregistration). Performance improvements: unpin_user_pages() for hugetlbfs and THP improves ~3x (through gup_test) and RDMA MR dereg improves ~4.5x with the new API. See patches 2 and 4 for those. This patch (of 4): Add a helper that iterates over head pages in a list of pages. It essentially counts the tails until the next page to process has a different head that the current. This is going to be used by unpin_user_pages() family of functions, to batch the head page refcount updates once for all passed consecutive tail pages. Link: https://lkml.kernel.org/r/20210212130843.13865-1-joao.m.martins@oracle.com Link: https://lkml.kernel.org/r/20210212130843.13865-2-joao.m.martins@oracle.com Signed-off-by: Joao Martins <joao.m.martins@oracle.com> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Cc: Doug Ledford <dledford@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 13:55:44 +08:00
unsigned int nr;
for (nr = i + 1; nr < npages; nr++) {
if (page_folio(list[nr]) != folio)
mm/gup: add compound page list iterator Patch series "mm/gup: page unpining improvements", v4. This series improves page unpinning, with an eye on improving MR deregistration for big swaths of memory (which is bound by the page unpining), particularly: 1) Decrement the head page by @ntails and thus reducing a lot the number of atomic operations per compound page. This is done by comparing individual tail pages heads, and counting number of consecutive tails on which they match heads and based on that update head page refcount. Should have a visible improvement in all page (un)pinners which use compound pages 2) Introducing a new API for unpinning page ranges (to avoid the trick in the previous item and be based on math), and use that in RDMA ib_mem_release (used for mr deregistration). Performance improvements: unpin_user_pages() for hugetlbfs and THP improves ~3x (through gup_test) and RDMA MR dereg improves ~4.5x with the new API. See patches 2 and 4 for those. This patch (of 4): Add a helper that iterates over head pages in a list of pages. It essentially counts the tails until the next page to process has a different head that the current. This is going to be used by unpin_user_pages() family of functions, to batch the head page refcount updates once for all passed consecutive tail pages. Link: https://lkml.kernel.org/r/20210212130843.13865-1-joao.m.martins@oracle.com Link: https://lkml.kernel.org/r/20210212130843.13865-2-joao.m.martins@oracle.com Signed-off-by: Joao Martins <joao.m.martins@oracle.com> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Cc: Doug Ledford <dledford@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 13:55:44 +08:00
break;
}
*ntails = nr - i;
return folio;
mm/gup: add compound page list iterator Patch series "mm/gup: page unpining improvements", v4. This series improves page unpinning, with an eye on improving MR deregistration for big swaths of memory (which is bound by the page unpining), particularly: 1) Decrement the head page by @ntails and thus reducing a lot the number of atomic operations per compound page. This is done by comparing individual tail pages heads, and counting number of consecutive tails on which they match heads and based on that update head page refcount. Should have a visible improvement in all page (un)pinners which use compound pages 2) Introducing a new API for unpinning page ranges (to avoid the trick in the previous item and be based on math), and use that in RDMA ib_mem_release (used for mr deregistration). Performance improvements: unpin_user_pages() for hugetlbfs and THP improves ~3x (through gup_test) and RDMA MR dereg improves ~4.5x with the new API. See patches 2 and 4 for those. This patch (of 4): Add a helper that iterates over head pages in a list of pages. It essentially counts the tails until the next page to process has a different head that the current. This is going to be used by unpin_user_pages() family of functions, to batch the head page refcount updates once for all passed consecutive tail pages. Link: https://lkml.kernel.org/r/20210212130843.13865-1-joao.m.martins@oracle.com Link: https://lkml.kernel.org/r/20210212130843.13865-2-joao.m.martins@oracle.com Signed-off-by: Joao Martins <joao.m.martins@oracle.com> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Cc: Doug Ledford <dledford@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 13:55:44 +08:00
}
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
/**
* unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
mm/gup: add make_dirty arg to put_user_pages_dirty_lock() [11~From: John Hubbard <jhubbard@nvidia.com> Subject: mm/gup: add make_dirty arg to put_user_pages_dirty_lock() Patch series "mm/gup: add make_dirty arg to put_user_pages_dirty_lock()", v3. There are about 50+ patches in my tree [2], and I'll be sending out the remaining ones in a few more groups: * The block/bio related changes (Jerome mostly wrote those, but I've had to move stuff around extensively, and add a little code) * mm/ changes * other subsystem patches * an RFC that shows the current state of the tracking patch set. That can only be applied after all call sites are converted, but it's good to get an early look at it. This is part a tree-wide conversion, as described in fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). This patch (of 3): Provide more capable variation of put_user_pages_dirty_lock(), and delete put_user_pages_dirty(). This is based on the following: 1. Lots of call sites become simpler if a bool is passed into put_user_page*(), instead of making the call site choose which put_user_page*() variant to call. 2. Christoph Hellwig's observation that set_page_dirty_lock() is usually correct, and set_page_dirty() is usually a bug, or at least questionable, within a put_user_page*() calling chain. This leads to the following API choices: * put_user_pages_dirty_lock(page, npages, make_dirty) * There is no put_user_pages_dirty(). You have to hand code that, in the rare case that it's required. [jhubbard@nvidia.com: remove unused variable in siw_free_plist()] Link: http://lkml.kernel.org/r/20190729074306.10368-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20190724044537.10458-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 06:35:04 +08:00
* @pages: array of pages to be maybe marked dirty, and definitely released.
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
* @npages: number of pages in the @pages array.
mm/gup: add make_dirty arg to put_user_pages_dirty_lock() [11~From: John Hubbard <jhubbard@nvidia.com> Subject: mm/gup: add make_dirty arg to put_user_pages_dirty_lock() Patch series "mm/gup: add make_dirty arg to put_user_pages_dirty_lock()", v3. There are about 50+ patches in my tree [2], and I'll be sending out the remaining ones in a few more groups: * The block/bio related changes (Jerome mostly wrote those, but I've had to move stuff around extensively, and add a little code) * mm/ changes * other subsystem patches * an RFC that shows the current state of the tracking patch set. That can only be applied after all call sites are converted, but it's good to get an early look at it. This is part a tree-wide conversion, as described in fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). This patch (of 3): Provide more capable variation of put_user_pages_dirty_lock(), and delete put_user_pages_dirty(). This is based on the following: 1. Lots of call sites become simpler if a bool is passed into put_user_page*(), instead of making the call site choose which put_user_page*() variant to call. 2. Christoph Hellwig's observation that set_page_dirty_lock() is usually correct, and set_page_dirty() is usually a bug, or at least questionable, within a put_user_page*() calling chain. This leads to the following API choices: * put_user_pages_dirty_lock(page, npages, make_dirty) * There is no put_user_pages_dirty(). You have to hand code that, in the rare case that it's required. [jhubbard@nvidia.com: remove unused variable in siw_free_plist()] Link: http://lkml.kernel.org/r/20190729074306.10368-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20190724044537.10458-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 06:35:04 +08:00
* @make_dirty: whether to mark the pages dirty
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
*
* "gup-pinned page" refers to a page that has had one of the get_user_pages()
* variants called on that page.
*
* For each page in the @pages array, make that page (or its head page, if a
mm/gup: add make_dirty arg to put_user_pages_dirty_lock() [11~From: John Hubbard <jhubbard@nvidia.com> Subject: mm/gup: add make_dirty arg to put_user_pages_dirty_lock() Patch series "mm/gup: add make_dirty arg to put_user_pages_dirty_lock()", v3. There are about 50+ patches in my tree [2], and I'll be sending out the remaining ones in a few more groups: * The block/bio related changes (Jerome mostly wrote those, but I've had to move stuff around extensively, and add a little code) * mm/ changes * other subsystem patches * an RFC that shows the current state of the tracking patch set. That can only be applied after all call sites are converted, but it's good to get an early look at it. This is part a tree-wide conversion, as described in fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). This patch (of 3): Provide more capable variation of put_user_pages_dirty_lock(), and delete put_user_pages_dirty(). This is based on the following: 1. Lots of call sites become simpler if a bool is passed into put_user_page*(), instead of making the call site choose which put_user_page*() variant to call. 2. Christoph Hellwig's observation that set_page_dirty_lock() is usually correct, and set_page_dirty() is usually a bug, or at least questionable, within a put_user_page*() calling chain. This leads to the following API choices: * put_user_pages_dirty_lock(page, npages, make_dirty) * There is no put_user_pages_dirty(). You have to hand code that, in the rare case that it's required. [jhubbard@nvidia.com: remove unused variable in siw_free_plist()] Link: http://lkml.kernel.org/r/20190729074306.10368-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20190724044537.10458-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 06:35:04 +08:00
* compound page) dirty, if @make_dirty is true, and if the page was previously
* listed as clean. In any case, releases all pages using unpin_user_page(),
* possibly via unpin_user_pages(), for the non-dirty case.
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
*
* Please see the unpin_user_page() documentation for details.
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
*
mm/gup: add make_dirty arg to put_user_pages_dirty_lock() [11~From: John Hubbard <jhubbard@nvidia.com> Subject: mm/gup: add make_dirty arg to put_user_pages_dirty_lock() Patch series "mm/gup: add make_dirty arg to put_user_pages_dirty_lock()", v3. There are about 50+ patches in my tree [2], and I'll be sending out the remaining ones in a few more groups: * The block/bio related changes (Jerome mostly wrote those, but I've had to move stuff around extensively, and add a little code) * mm/ changes * other subsystem patches * an RFC that shows the current state of the tracking patch set. That can only be applied after all call sites are converted, but it's good to get an early look at it. This is part a tree-wide conversion, as described in fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). This patch (of 3): Provide more capable variation of put_user_pages_dirty_lock(), and delete put_user_pages_dirty(). This is based on the following: 1. Lots of call sites become simpler if a bool is passed into put_user_page*(), instead of making the call site choose which put_user_page*() variant to call. 2. Christoph Hellwig's observation that set_page_dirty_lock() is usually correct, and set_page_dirty() is usually a bug, or at least questionable, within a put_user_page*() calling chain. This leads to the following API choices: * put_user_pages_dirty_lock(page, npages, make_dirty) * There is no put_user_pages_dirty(). You have to hand code that, in the rare case that it's required. [jhubbard@nvidia.com: remove unused variable in siw_free_plist()] Link: http://lkml.kernel.org/r/20190729074306.10368-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20190724044537.10458-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 06:35:04 +08:00
* set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
* required, then the caller should a) verify that this is really correct,
* because _lock() is usually required, and b) hand code it:
* set_page_dirty_lock(), unpin_user_page().
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
*
*/
void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
bool make_dirty)
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
{
unsigned long i;
struct folio *folio;
unsigned int nr;
mm/gup: add make_dirty arg to put_user_pages_dirty_lock() [11~From: John Hubbard <jhubbard@nvidia.com> Subject: mm/gup: add make_dirty arg to put_user_pages_dirty_lock() Patch series "mm/gup: add make_dirty arg to put_user_pages_dirty_lock()", v3. There are about 50+ patches in my tree [2], and I'll be sending out the remaining ones in a few more groups: * The block/bio related changes (Jerome mostly wrote those, but I've had to move stuff around extensively, and add a little code) * mm/ changes * other subsystem patches * an RFC that shows the current state of the tracking patch set. That can only be applied after all call sites are converted, but it's good to get an early look at it. This is part a tree-wide conversion, as described in fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). This patch (of 3): Provide more capable variation of put_user_pages_dirty_lock(), and delete put_user_pages_dirty(). This is based on the following: 1. Lots of call sites become simpler if a bool is passed into put_user_page*(), instead of making the call site choose which put_user_page*() variant to call. 2. Christoph Hellwig's observation that set_page_dirty_lock() is usually correct, and set_page_dirty() is usually a bug, or at least questionable, within a put_user_page*() calling chain. This leads to the following API choices: * put_user_pages_dirty_lock(page, npages, make_dirty) * There is no put_user_pages_dirty(). You have to hand code that, in the rare case that it's required. [jhubbard@nvidia.com: remove unused variable in siw_free_plist()] Link: http://lkml.kernel.org/r/20190729074306.10368-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20190724044537.10458-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 06:35:04 +08:00
if (!make_dirty) {
unpin_user_pages(pages, npages);
mm/gup: add make_dirty arg to put_user_pages_dirty_lock() [11~From: John Hubbard <jhubbard@nvidia.com> Subject: mm/gup: add make_dirty arg to put_user_pages_dirty_lock() Patch series "mm/gup: add make_dirty arg to put_user_pages_dirty_lock()", v3. There are about 50+ patches in my tree [2], and I'll be sending out the remaining ones in a few more groups: * The block/bio related changes (Jerome mostly wrote those, but I've had to move stuff around extensively, and add a little code) * mm/ changes * other subsystem patches * an RFC that shows the current state of the tracking patch set. That can only be applied after all call sites are converted, but it's good to get an early look at it. This is part a tree-wide conversion, as described in fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). This patch (of 3): Provide more capable variation of put_user_pages_dirty_lock(), and delete put_user_pages_dirty(). This is based on the following: 1. Lots of call sites become simpler if a bool is passed into put_user_page*(), instead of making the call site choose which put_user_page*() variant to call. 2. Christoph Hellwig's observation that set_page_dirty_lock() is usually correct, and set_page_dirty() is usually a bug, or at least questionable, within a put_user_page*() calling chain. This leads to the following API choices: * put_user_pages_dirty_lock(page, npages, make_dirty) * There is no put_user_pages_dirty(). You have to hand code that, in the rare case that it's required. [jhubbard@nvidia.com: remove unused variable in siw_free_plist()] Link: http://lkml.kernel.org/r/20190729074306.10368-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20190724044537.10458-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 06:35:04 +08:00
return;
}
mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Let's verify when (un)pinning anonymous pages that we always deal with exclusive anonymous pages, which guarantees that we'll have a reliable PIN, meaning that we cannot end up with the GUP pin being inconsistent with he pages mapped into the page tables due to a COW triggered by a write fault. When pinning pages, after conditionally triggering GUP unsharing of possibly shared anonymous pages, we should always only see exclusive anonymous pages. Note that anonymous pages that are mapped writable must be marked exclusive, otherwise we'd have a BUG. When pinning during ordinary GUP, simply add a check after our conditional GUP-triggered unsharing checks. As we know exactly how the page is mapped, we know exactly in which page we have to check for PageAnonExclusive(). When pinning via GUP-fast we have to be careful, because we can race with fork(): verify only after we made sure via the seqcount that we didn't race with concurrent fork() that we didn't end up pinning a possibly shared anonymous page. Similarly, when unpinning, verify that the pages are still marked as exclusive: otherwise something turned the pages possibly shared, which can result in random memory corruptions, which we really want to catch. With only the pinned pages at hand and not the actual page table entries we have to be a bit careful: hugetlb pages are always mapped via a single logical page table entry referencing the head page and PG_anon_exclusive of the head page applies. Anon THP are a bit more complicated, because we might have obtained the page reference either via a PMD or a PTE -- depending on the mapping type we either have to check PageAnonExclusive of the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies: as we don't know and to make our life easier, check that either is set. Take care to not verify in case we're unpinning during GUP-fast because we detected concurrent fork(): we might stumble over an anonymous page that is now shared. Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
sanity_check_pinned_pages(pages, npages);
for (i = 0; i < npages; i += nr) {
folio = gup_folio_next(pages, npages, i, &nr);
mm/gup: add make_dirty arg to put_user_pages_dirty_lock() [11~From: John Hubbard <jhubbard@nvidia.com> Subject: mm/gup: add make_dirty arg to put_user_pages_dirty_lock() Patch series "mm/gup: add make_dirty arg to put_user_pages_dirty_lock()", v3. There are about 50+ patches in my tree [2], and I'll be sending out the remaining ones in a few more groups: * The block/bio related changes (Jerome mostly wrote those, but I've had to move stuff around extensively, and add a little code) * mm/ changes * other subsystem patches * an RFC that shows the current state of the tracking patch set. That can only be applied after all call sites are converted, but it's good to get an early look at it. This is part a tree-wide conversion, as described in fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). This patch (of 3): Provide more capable variation of put_user_pages_dirty_lock(), and delete put_user_pages_dirty(). This is based on the following: 1. Lots of call sites become simpler if a bool is passed into put_user_page*(), instead of making the call site choose which put_user_page*() variant to call. 2. Christoph Hellwig's observation that set_page_dirty_lock() is usually correct, and set_page_dirty() is usually a bug, or at least questionable, within a put_user_page*() calling chain. This leads to the following API choices: * put_user_pages_dirty_lock(page, npages, make_dirty) * There is no put_user_pages_dirty(). You have to hand code that, in the rare case that it's required. [jhubbard@nvidia.com: remove unused variable in siw_free_plist()] Link: http://lkml.kernel.org/r/20190729074306.10368-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20190724044537.10458-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 06:35:04 +08:00
/*
* Checking PageDirty at this point may race with
* clear_page_dirty_for_io(), but that's OK. Two key
* cases:
*
* 1) This code sees the page as already dirty, so it
* skips the call to set_page_dirty(). That could happen
* because clear_page_dirty_for_io() called
* page_mkclean(), followed by set_page_dirty().
* However, now the page is going to get written back,
* which meets the original intention of setting it
* dirty, so all is well: clear_page_dirty_for_io() goes
* on to call TestClearPageDirty(), and write the page
* back.
*
* 2) This code sees the page as clean, so it calls
* set_page_dirty(). The page stays dirty, despite being
* written back, so it gets written back again in the
* next writeback cycle. This is harmless.
*/
if (!folio_test_dirty(folio)) {
folio_lock(folio);
folio_mark_dirty(folio);
folio_unlock(folio);
}
gup_put_folio(folio, nr, FOLL_PIN);
mm/gup: add make_dirty arg to put_user_pages_dirty_lock() [11~From: John Hubbard <jhubbard@nvidia.com> Subject: mm/gup: add make_dirty arg to put_user_pages_dirty_lock() Patch series "mm/gup: add make_dirty arg to put_user_pages_dirty_lock()", v3. There are about 50+ patches in my tree [2], and I'll be sending out the remaining ones in a few more groups: * The block/bio related changes (Jerome mostly wrote those, but I've had to move stuff around extensively, and add a little code) * mm/ changes * other subsystem patches * an RFC that shows the current state of the tracking patch set. That can only be applied after all call sites are converted, but it's good to get an early look at it. This is part a tree-wide conversion, as described in fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). This patch (of 3): Provide more capable variation of put_user_pages_dirty_lock(), and delete put_user_pages_dirty(). This is based on the following: 1. Lots of call sites become simpler if a bool is passed into put_user_page*(), instead of making the call site choose which put_user_page*() variant to call. 2. Christoph Hellwig's observation that set_page_dirty_lock() is usually correct, and set_page_dirty() is usually a bug, or at least questionable, within a put_user_page*() calling chain. This leads to the following API choices: * put_user_pages_dirty_lock(page, npages, make_dirty) * There is no put_user_pages_dirty(). You have to hand code that, in the rare case that it's required. [jhubbard@nvidia.com: remove unused variable in siw_free_plist()] Link: http://lkml.kernel.org/r/20190729074306.10368-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20190724044537.10458-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 06:35:04 +08:00
}
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
}
EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
/**
* unpin_user_page_range_dirty_lock() - release and optionally dirty
* gup-pinned page range
*
* @page: the starting page of a range maybe marked dirty, and definitely released.
* @npages: number of consecutive pages to release.
* @make_dirty: whether to mark the pages dirty
*
* "gup-pinned page range" refers to a range of pages that has had one of the
* pin_user_pages() variants called on that page.
*
* For the page ranges defined by [page .. page+npages], make that range (or
* its head pages, if a compound page) dirty, if @make_dirty is true, and if the
* page range was previously listed as clean.
*
* set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
* required, then the caller should a) verify that this is really correct,
* because _lock() is usually required, and b) hand code it:
* set_page_dirty_lock(), unpin_user_page().
*
*/
void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
bool make_dirty)
{
unsigned long i;
struct folio *folio;
unsigned int nr;
for (i = 0; i < npages; i += nr) {
folio = gup_folio_range_next(page, npages, i, &nr);
if (make_dirty && !folio_test_dirty(folio)) {
folio_lock(folio);
folio_mark_dirty(folio);
folio_unlock(folio);
}
gup_put_folio(folio, nr, FOLL_PIN);
}
}
EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Let's verify when (un)pinning anonymous pages that we always deal with exclusive anonymous pages, which guarantees that we'll have a reliable PIN, meaning that we cannot end up with the GUP pin being inconsistent with he pages mapped into the page tables due to a COW triggered by a write fault. When pinning pages, after conditionally triggering GUP unsharing of possibly shared anonymous pages, we should always only see exclusive anonymous pages. Note that anonymous pages that are mapped writable must be marked exclusive, otherwise we'd have a BUG. When pinning during ordinary GUP, simply add a check after our conditional GUP-triggered unsharing checks. As we know exactly how the page is mapped, we know exactly in which page we have to check for PageAnonExclusive(). When pinning via GUP-fast we have to be careful, because we can race with fork(): verify only after we made sure via the seqcount that we didn't race with concurrent fork() that we didn't end up pinning a possibly shared anonymous page. Similarly, when unpinning, verify that the pages are still marked as exclusive: otherwise something turned the pages possibly shared, which can result in random memory corruptions, which we really want to catch. With only the pinned pages at hand and not the actual page table entries we have to be a bit careful: hugetlb pages are always mapped via a single logical page table entry referencing the head page and PG_anon_exclusive of the head page applies. Anon THP are a bit more complicated, because we might have obtained the page reference either via a PMD or a PTE -- depending on the mapping type we either have to check PageAnonExclusive of the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies: as we don't know and to make our life easier, check that either is set. Take care to not verify in case we're unpinning during GUP-fast because we detected concurrent fork(): we might stumble over an anonymous page that is now shared. Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
static void unpin_user_pages_lockless(struct page **pages, unsigned long npages)
{
unsigned long i;
struct folio *folio;
unsigned int nr;
/*
* Don't perform any sanity checks because we might have raced with
* fork() and some anonymous pages might now actually be shared --
* which is why we're unpinning after all.
*/
for (i = 0; i < npages; i += nr) {
folio = gup_folio_next(pages, npages, i, &nr);
gup_put_folio(folio, nr, FOLL_PIN);
}
}
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
/**
* unpin_user_pages() - release an array of gup-pinned pages.
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
* @pages: array of pages to be marked dirty and released.
* @npages: number of pages in the @pages array.
*
* For each page in the @pages array, release the page using unpin_user_page().
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
*
* Please see the unpin_user_page() documentation for details.
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
*/
void unpin_user_pages(struct page **pages, unsigned long npages)
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
{
unsigned long i;
struct folio *folio;
unsigned int nr;
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
/*
* If this WARN_ON() fires, then the system *might* be leaking pages (by
* leaving them pinned), but probably not. More likely, gup/pup returned
* a hard -ERRNO error to the caller, who erroneously passed it here.
*/
if (WARN_ON(IS_ERR_VALUE(npages)))
return;
mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Let's verify when (un)pinning anonymous pages that we always deal with exclusive anonymous pages, which guarantees that we'll have a reliable PIN, meaning that we cannot end up with the GUP pin being inconsistent with he pages mapped into the page tables due to a COW triggered by a write fault. When pinning pages, after conditionally triggering GUP unsharing of possibly shared anonymous pages, we should always only see exclusive anonymous pages. Note that anonymous pages that are mapped writable must be marked exclusive, otherwise we'd have a BUG. When pinning during ordinary GUP, simply add a check after our conditional GUP-triggered unsharing checks. As we know exactly how the page is mapped, we know exactly in which page we have to check for PageAnonExclusive(). When pinning via GUP-fast we have to be careful, because we can race with fork(): verify only after we made sure via the seqcount that we didn't race with concurrent fork() that we didn't end up pinning a possibly shared anonymous page. Similarly, when unpinning, verify that the pages are still marked as exclusive: otherwise something turned the pages possibly shared, which can result in random memory corruptions, which we really want to catch. With only the pinned pages at hand and not the actual page table entries we have to be a bit careful: hugetlb pages are always mapped via a single logical page table entry referencing the head page and PG_anon_exclusive of the head page applies. Anon THP are a bit more complicated, because we might have obtained the page reference either via a PMD or a PTE -- depending on the mapping type we either have to check PageAnonExclusive of the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies: as we don't know and to make our life easier, check that either is set. Take care to not verify in case we're unpinning during GUP-fast because we detected concurrent fork(): we might stumble over an anonymous page that is now shared. Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
sanity_check_pinned_pages(pages, npages);
for (i = 0; i < npages; i += nr) {
folio = gup_folio_next(pages, npages, i, &nr);
gup_put_folio(folio, nr, FOLL_PIN);
}
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
}
EXPORT_SYMBOL(unpin_user_pages);
mm: introduce put_user_page*(), placeholder versions A discussion of the overall problem is below. As mentioned in patch 0001, the steps are to fix the problem are: 1) Provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. Overview ======== Some kernel components (file systems, device drivers) need to access memory that is specified via process virtual address. For a long time, the API to achieve that was get_user_pages ("GUP") and its variations. However, GUP has critical limitations that have been overlooked; in particular, GUP does not interact correctly with filesystems in all situations. That means that file-backed memory + GUP is a recipe for potential problems, some of which have already occurred in the field. GUP was first introduced for Direct IO (O_DIRECT), allowing filesystem code to get the struct page behind a virtual address and to let storage hardware perform a direct copy to or from that page. This is a short-lived access pattern, and as such, the window for a concurrent writeback of GUP'd page was small enough that there were not (we think) any reported problems. Also, userspace was expected to understand and accept that Direct IO was not synchronized with memory-mapped access to that data, nor with any process address space changes such as munmap(), mremap(), etc. Over the years, more GUP uses have appeared (virtualization, device drivers, RDMA) that can keep the pages they get via GUP for a long period of time (seconds, minutes, hours, days, ...). This long-term pinning makes an underlying design problem more obvious. In fact, there are a number of key problems inherent to GUP: Interactions with file systems ============================== File systems expect to be able to write back data, both to reclaim pages, and for data integrity. Allowing other hardware (NICs, GPUs, etc) to gain write access to the file memory pages means that such hardware can dirty the pages, without the filesystem being aware. This can, in some cases (depending on filesystem, filesystem options, block device, block device options, and other variables), lead to data corruption, and also to kernel bugs of the form: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. Long term GUP ============= Long term GUP is an issue when FOLL_WRITE is specified to GUP (so, a writeable mapping is created), and the pages are file-backed. That can lead to filesystem corruption. What happens is that when a file-backed page is being written back, it is first mapped read-only in all of the CPU page tables; the file system then assumes that nobody can write to the page, and that the page content is therefore stable. Unfortunately, the GUP callers generally do not monitor changes to the CPU pages tables; they instead assume that the following pattern is safe (it's not): get_user_pages() Hardware can keep a reference to those pages for a very long time, and write to it at any time. Because "hardware" here means "devices that are not a CPU", this activity occurs without any interaction with the kernel's file system code. for each page set_page_dirty put_page() In fact, the GUP documentation even recommends that pattern. Anyway, the file system assumes that the page is stable (nothing is writing to the page), and that is a problem: stable page content is necessary for many filesystem actions during writeback, such as checksum, encryption, RAID striping, etc. Furthermore, filesystem features like COW (copy on write) or snapshot also rely on being able to use a new page for as memory for that memory range inside the file. Corruption during write back is clearly possible here. To solve that, one idea is to identify pages that have active GUP, so that we can use a bounce page to write stable data to the filesystem. The filesystem would work on the bounce page, while any of the active GUP might write to the original page. This would avoid the stable page violation problem, but note that it is only part of the overall solution, because other problems remain. Other filesystem features that need to replace the page with a new one can be inhibited for pages that are GUP-pinned. This will, however, alter and limit some of those filesystem features. The only fix for that would be to require GUP users to monitor and respond to CPU page table updates. Subsystems such as ODP and HMM do this, for example. This aspect of the problem is still under discussion. Direct IO ========= Direct IO can cause corruption, if userspace does Direct-IO that writes to a range of virtual addresses that are mmap'd to a file. The pages written to are file-backed pages that can be under write back, while the Direct IO is taking place. Here, Direct IO races with a write back: it calls GUP before page_mkclean() has replaced the CPU pte with a read-only entry. The race window is pretty small, which is probably why years have gone by before we noticed this problem: Direct IO is generally very quick, and tends to finish up before the filesystem gets around to do anything with the page contents. However, it's still a real problem. The solution is to never let GUP return pages that are under write back, but instead, force GUP to take a write fault on those pages. That way, GUP will properly synchronize with the active write back. This does not change the required GUP behavior, it just avoids that race. Details ======= Introduces put_user_page(), which simply calls put_page(). This provides a way to update all get_user_pages*() callers, so that they call put_user_page(), instead of put_page(). Also introduces put_user_pages(), and a few dirty/locked variations, as a replacement for release_pages(), and also as a replacement for open-coded loops that release multiple pages. These may be used for subsequent performance improvements, via batching of pages to be released. This is the first step of fixing a problem (also described in [1] and [2]) with interactions between get_user_pages ("gup") and filesystems. Problem description: let's start with a bug report. Below, is what happens sometimes, under memory pressure, when a driver pins some pages via gup, and then marks those pages dirty, and releases them. Note that the gup documentation actually recommends that pattern. The problem is that the filesystem may do a writeback while the pages were gup-pinned, and then the filesystem believes that the pages are clean. So, when the driver later marks the pages as dirty, that conflicts with the filesystem's page tracking and results in a BUG(), like this one that I experienced: kernel BUG at /build/linux-fQ94TU/linux-4.4.0/fs/ext4/inode.c:1899! backtrace: ext4_writepage __writepage write_cache_pages ext4_writepages do_writepages __writeback_single_inode writeback_sb_inodes __writeback_inodes_wb wb_writeback wb_workfn process_one_work worker_thread kthread ret_from_fork ...which is due to the file system asserting that there are still buffer heads attached: ({ \ BUG_ON(!PagePrivate(page)); \ ((struct buffer_head *)page_private(page)); \ }) Dave Chinner's description of this is very clear: "The fundamental issue is that ->page_mkwrite must be called on every write access to a clean file backed page, not just the first one. How long the GUP reference lasts is irrelevant, if the page is clean and you need to dirty it, you must call ->page_mkwrite before it is marked writeable and dirtied. Every. Time." This is just one symptom of the larger design problem: real filesystems that actually write to a backing device, do not actually support get_user_pages() being called on their pages, and letting hardware write directly to those pages--even though that pattern has been going on since about 2005 or so. The steps are to fix it are: 1) (This patch): provide put_user_page*() routines, intended to be used for releasing pages that were pinned via get_user_pages*(). 2) Convert all of the call sites for get_user_pages*(), to invoke put_user_page*(), instead of put_page(). This involves dozens of call sites, and will take some time. 3) After (2) is complete, use get_user_pages*() and put_user_page*() to implement tracking of these pages. This tracking will be separate from the existing struct page refcounting. 4) Use the tracking and identification of these pages, to implement special handling (especially in writeback paths) when the pages are backed by a filesystem. [1] https://lwn.net/Articles/774411/ : "DMA and get_user_pages()" [2] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()" Link: http://lkml.kernel.org/r/20190327023632.13307-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [docs] Reviewed-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Christoph Lameter <cl@linux.com> Tested-by: Ira Weiny <ira.weiny@intel.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:19:08 +08:00
mm: gup: pack has_pinned in MMF_HAS_PINNED has_pinned 32bit can be packed in the MMF_HAS_PINNED bit as a noop cleanup. Any atomic_inc/dec to the mm cacheline shared by all threads in pin-fast would reintroduce a loss of SMP scalability to pin-fast, so there's no future potential usefulness to keep an atomic in the mm for this. set_bit(MMF_HAS_PINNED) will be theoretically a bit slower than WRITE_ONCE (atomic_set is equivalent to WRITE_ONCE), but the set_bit (just like atomic_set after this commit) has to be still issued only once per "mm", so the difference between the two will be lost in the noise. will-it-scale "mmap2" shows no change in performance with enterprise config as expected. will-it-scale "pin_fast" retains the > 4000% SMP scalability performance improvement against upstream as expected. This is a noop as far as overall performance and SMP scalability are concerned. [peterx@redhat.com: pack has_pinned in MMF_HAS_PINNED] Link: https://lkml.kernel.org/r/YJqWESqyxa8OZA+2@t490s [akpm@linux-foundation.org: coding style fixes] [peterx@redhat.com: fix build for task_mmu.c, introduce mm_set_has_pinned_flag, fix comments] Link: https://lkml.kernel.org/r/20210507150553.208763-4-peterx@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Kirill Shutemov <kirill@shutemov.name> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:36:40 +08:00
/*
* Set the MMF_HAS_PINNED if not set yet; after set it'll be there for the mm's
* lifecycle. Avoid setting the bit unless necessary, or it might cause write
* cache bouncing on large SMP machines for concurrent pinned gups.
*/
static inline void mm_set_has_pinned_flag(unsigned long *mm_flags)
{
if (!test_bit(MMF_HAS_PINNED, mm_flags))
set_bit(MMF_HAS_PINNED, mm_flags);
}
#ifdef CONFIG_MMU
static struct page *no_page_table(struct vm_area_struct *vma,
unsigned int flags)
{
/*
* When core dumping an enormous anonymous area that nobody
* has touched so far, we don't want to allocate unnecessary pages or
* page tables. Return error instead of NULL to skip handle_mm_fault,
* then get_dump_page() will return NULL to leave a hole in the dump.
* But we can only make this optimization where a hole would surely
* be zero-filled if handle_mm_fault() actually did handle it.
*/
if ((flags & FOLL_DUMP) &&
(vma_is_anonymous(vma) || !vma->vm_ops->fault))
return ERR_PTR(-EFAULT);
return NULL;
}
static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
pte_t *pte, unsigned int flags)
{
if (flags & FOLL_TOUCH) {
pte_t entry = *pte;
if (flags & FOLL_WRITE)
entry = pte_mkdirty(entry);
entry = pte_mkyoung(entry);
if (!pte_same(*pte, entry)) {
set_pte_at(vma->vm_mm, address, pte, entry);
update_mmu_cache(vma, address, pte);
}
}
/* Proper page table entry exists, but no corresponding struct page */
return -EEXIST;
}
mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW Ever since the Dirty COW (CVE-2016-5195) security issue happened, we know that FOLL_FORCE can be possibly dangerous, especially if there are races that can be exploited by user space. Right now, it would be sufficient to have some code that sets a PTE of a R/O-mapped shared page dirty, in order for it to erroneously become writable by FOLL_FORCE. The implications of setting a write-protected PTE dirty might not be immediately obvious to everyone. And in fact ever since commit 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte"), we can use UFFDIO_CONTINUE to map a shmem page R/O while marking the pte dirty. This can be used by unprivileged user space to modify tmpfs/shmem file content even if the user does not have write permissions to the file, and to bypass memfd write sealing -- Dirty COW restricted to tmpfs/shmem (CVE-2022-2590). To fix such security issues for good, the insight is that we really only need that fancy retry logic (FOLL_COW) for COW mappings that are not writable (!VM_WRITE). And in a COW mapping, we really only broke COW if we have an exclusive anonymous page mapped. If we have something else mapped, or the mapped anonymous page might be shared (!PageAnonExclusive), we have to trigger a write fault to break COW. If we don't find an exclusive anonymous page when we retry, we have to trigger COW breaking once again because something intervened. Let's move away from this mandatory-retry + dirty handling and rely on our PageAnonExclusive() flag for making a similar decision, to use the same COW logic as in other kernel parts here as well. In case we stumble over a PTE in a COW mapping that does not map an exclusive anonymous page, COW was not properly broken and we have to trigger a fake write-fault to break COW. Just like we do in can_change_pte_writable() added via commit 64fe24a3e05e ("mm/mprotect: try avoiding write faults for exclusive anonymous pages when changing protection") and commit 76aefad628aa ("mm/mprotect: fix soft-dirty check in can_change_pte_writable()"), take care of softdirty and uffd-wp manually. For example, a write() via /proc/self/mem to a uffd-wp-protected range has to fail instead of silently granting write access and bypassing the userspace fault handler. Note that FOLL_FORCE is not only used for debug access, but also triggered by applications without debug intentions, for example, when pinning pages via RDMA. This fixes CVE-2022-2590. Note that only x86_64 and aarch64 are affected, because only those support CONFIG_HAVE_ARCH_USERFAULTFD_MINOR. Fortunately, FOLL_COW is no longer required to handle FOLL_FORCE. So let's just get rid of it. Thanks to Nadav Amit for pointing out that the pte_dirty() check in FOLL_FORCE code is problematic and might be exploitable. Note 1: We don't check for the PTE being dirty because it doesn't matter for making a "was COWed" decision anymore, and whoever modifies the page has to set the page dirty either way. Note 2: Kernels before extended uffd-wp support and before PageAnonExclusive (< 5.19) can simply revert the problematic commit instead and be safe regarding UFFDIO_CONTINUE. A backport to v5.19 requires minor adjustments due to lack of vma_soft_dirty_enabled(). Link: https://lkml.kernel.org/r/20220809205640.70916-1-david@redhat.com Fixes: 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte") Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: David Laight <David.Laight@ACULAB.COM> Cc: <stable@vger.kernel.org> [5.16] Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-08-10 04:56:40 +08:00
/* FOLL_FORCE can write to even unwritable PTEs in COW mappings. */
static inline bool can_follow_write_pte(pte_t pte, struct page *page,
struct vm_area_struct *vma,
unsigned int flags)
2016-10-14 04:07:36 +08:00
{
mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW Ever since the Dirty COW (CVE-2016-5195) security issue happened, we know that FOLL_FORCE can be possibly dangerous, especially if there are races that can be exploited by user space. Right now, it would be sufficient to have some code that sets a PTE of a R/O-mapped shared page dirty, in order for it to erroneously become writable by FOLL_FORCE. The implications of setting a write-protected PTE dirty might not be immediately obvious to everyone. And in fact ever since commit 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte"), we can use UFFDIO_CONTINUE to map a shmem page R/O while marking the pte dirty. This can be used by unprivileged user space to modify tmpfs/shmem file content even if the user does not have write permissions to the file, and to bypass memfd write sealing -- Dirty COW restricted to tmpfs/shmem (CVE-2022-2590). To fix such security issues for good, the insight is that we really only need that fancy retry logic (FOLL_COW) for COW mappings that are not writable (!VM_WRITE). And in a COW mapping, we really only broke COW if we have an exclusive anonymous page mapped. If we have something else mapped, or the mapped anonymous page might be shared (!PageAnonExclusive), we have to trigger a write fault to break COW. If we don't find an exclusive anonymous page when we retry, we have to trigger COW breaking once again because something intervened. Let's move away from this mandatory-retry + dirty handling and rely on our PageAnonExclusive() flag for making a similar decision, to use the same COW logic as in other kernel parts here as well. In case we stumble over a PTE in a COW mapping that does not map an exclusive anonymous page, COW was not properly broken and we have to trigger a fake write-fault to break COW. Just like we do in can_change_pte_writable() added via commit 64fe24a3e05e ("mm/mprotect: try avoiding write faults for exclusive anonymous pages when changing protection") and commit 76aefad628aa ("mm/mprotect: fix soft-dirty check in can_change_pte_writable()"), take care of softdirty and uffd-wp manually. For example, a write() via /proc/self/mem to a uffd-wp-protected range has to fail instead of silently granting write access and bypassing the userspace fault handler. Note that FOLL_FORCE is not only used for debug access, but also triggered by applications without debug intentions, for example, when pinning pages via RDMA. This fixes CVE-2022-2590. Note that only x86_64 and aarch64 are affected, because only those support CONFIG_HAVE_ARCH_USERFAULTFD_MINOR. Fortunately, FOLL_COW is no longer required to handle FOLL_FORCE. So let's just get rid of it. Thanks to Nadav Amit for pointing out that the pte_dirty() check in FOLL_FORCE code is problematic and might be exploitable. Note 1: We don't check for the PTE being dirty because it doesn't matter for making a "was COWed" decision anymore, and whoever modifies the page has to set the page dirty either way. Note 2: Kernels before extended uffd-wp support and before PageAnonExclusive (< 5.19) can simply revert the problematic commit instead and be safe regarding UFFDIO_CONTINUE. A backport to v5.19 requires minor adjustments due to lack of vma_soft_dirty_enabled(). Link: https://lkml.kernel.org/r/20220809205640.70916-1-david@redhat.com Fixes: 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte") Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: David Laight <David.Laight@ACULAB.COM> Cc: <stable@vger.kernel.org> [5.16] Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-08-10 04:56:40 +08:00
/* If the pte is writable, we can write to the page. */
if (pte_write(pte))
return true;
/* Maybe FOLL_FORCE is set to override it? */
if (!(flags & FOLL_FORCE))
return false;
/* But FOLL_FORCE has no effect on shared mappings */
if (vma->vm_flags & (VM_MAYSHARE | VM_SHARED))
return false;
/* ... or read-only private ones */
if (!(vma->vm_flags & VM_MAYWRITE))
return false;
/* ... or already writable ones that just need to take a write fault */
if (vma->vm_flags & VM_WRITE)
return false;
/*
* See can_change_pte_writable(): we broke COW and could map the page
* writable if we have an exclusive anonymous page ...
*/
if (!page || !PageAnon(page) || !PageAnonExclusive(page))
return false;
/* ... and a write-fault isn't required for other reasons. */
if (vma_soft_dirty_enabled(vma) && !pte_soft_dirty(pte))
return false;
return !userfaultfd_pte_wp(vma, pte);
2016-10-14 04:07:36 +08:00
}
static struct page *follow_page_pte(struct vm_area_struct *vma,
unsigned long address, pmd_t *pmd, unsigned int flags,
struct dev_pagemap **pgmap)
{
struct mm_struct *mm = vma->vm_mm;
struct page *page;
spinlock_t *ptl;
pte_t *ptep, pte;
mm/gup/writeback: add callbacks for inaccessible pages With the introduction of protected KVM guests on s390 there is now a concept of inaccessible pages. These pages need to be made accessible before the host can access them. While cpu accesses will trigger a fault that can be resolved, I/O accesses will just fail. We need to add a callback into architecture code for places that will do I/O, namely when writeback is started or when a page reference is taken. This is not only to enable paging, file backing etc, it is also necessary to protect the host against a malicious user space. For example a bad QEMU could simply start direct I/O on such protected memory. We do not want userspace to be able to trigger I/O errors and thus the logic is "whenever somebody accesses that page (gup) or does I/O, make sure that this page can be accessed". When the guest tries to access that page we will wait in the page fault handler for writeback to have finished and for the page_ref to be the expected value. On s390x the function is not supposed to fail, so it is ok to use a WARN_ON on failure. If we ever need some more finegrained handling we can tackle this when we know the details. Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Acked-by: Will Deacon <will@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Matthew Wilcox <willy@infradead.org> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200306132537.783769-3-imbrenda@linux.ibm.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:56 +08:00
int ret;
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
/* FOLL_GET and FOLL_PIN are mutually exclusive. */
if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
(FOLL_PIN | FOLL_GET)))
return ERR_PTR(-EINVAL);
if (unlikely(pmd_bad(*pmd)))
return no_page_table(vma, flags);
ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
pte = *ptep;
if (!pte_present(pte))
goto no_page;
if (pte_protnone(pte) && !gup_can_follow_protnone(flags))
goto no_page;
page = vm_normal_page(vma, address, pte);
mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW Ever since the Dirty COW (CVE-2016-5195) security issue happened, we know that FOLL_FORCE can be possibly dangerous, especially if there are races that can be exploited by user space. Right now, it would be sufficient to have some code that sets a PTE of a R/O-mapped shared page dirty, in order for it to erroneously become writable by FOLL_FORCE. The implications of setting a write-protected PTE dirty might not be immediately obvious to everyone. And in fact ever since commit 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte"), we can use UFFDIO_CONTINUE to map a shmem page R/O while marking the pte dirty. This can be used by unprivileged user space to modify tmpfs/shmem file content even if the user does not have write permissions to the file, and to bypass memfd write sealing -- Dirty COW restricted to tmpfs/shmem (CVE-2022-2590). To fix such security issues for good, the insight is that we really only need that fancy retry logic (FOLL_COW) for COW mappings that are not writable (!VM_WRITE). And in a COW mapping, we really only broke COW if we have an exclusive anonymous page mapped. If we have something else mapped, or the mapped anonymous page might be shared (!PageAnonExclusive), we have to trigger a write fault to break COW. If we don't find an exclusive anonymous page when we retry, we have to trigger COW breaking once again because something intervened. Let's move away from this mandatory-retry + dirty handling and rely on our PageAnonExclusive() flag for making a similar decision, to use the same COW logic as in other kernel parts here as well. In case we stumble over a PTE in a COW mapping that does not map an exclusive anonymous page, COW was not properly broken and we have to trigger a fake write-fault to break COW. Just like we do in can_change_pte_writable() added via commit 64fe24a3e05e ("mm/mprotect: try avoiding write faults for exclusive anonymous pages when changing protection") and commit 76aefad628aa ("mm/mprotect: fix soft-dirty check in can_change_pte_writable()"), take care of softdirty and uffd-wp manually. For example, a write() via /proc/self/mem to a uffd-wp-protected range has to fail instead of silently granting write access and bypassing the userspace fault handler. Note that FOLL_FORCE is not only used for debug access, but also triggered by applications without debug intentions, for example, when pinning pages via RDMA. This fixes CVE-2022-2590. Note that only x86_64 and aarch64 are affected, because only those support CONFIG_HAVE_ARCH_USERFAULTFD_MINOR. Fortunately, FOLL_COW is no longer required to handle FOLL_FORCE. So let's just get rid of it. Thanks to Nadav Amit for pointing out that the pte_dirty() check in FOLL_FORCE code is problematic and might be exploitable. Note 1: We don't check for the PTE being dirty because it doesn't matter for making a "was COWed" decision anymore, and whoever modifies the page has to set the page dirty either way. Note 2: Kernels before extended uffd-wp support and before PageAnonExclusive (< 5.19) can simply revert the problematic commit instead and be safe regarding UFFDIO_CONTINUE. A backport to v5.19 requires minor adjustments due to lack of vma_soft_dirty_enabled(). Link: https://lkml.kernel.org/r/20220809205640.70916-1-david@redhat.com Fixes: 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in mfill_atomic_install_pte") Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: David Laight <David.Laight@ACULAB.COM> Cc: <stable@vger.kernel.org> [5.16] Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-08-10 04:56:40 +08:00
/*
* We only care about anon pages in can_follow_write_pte() and don't
* have to worry about pte_devmap() because they are never anon.
*/
if ((flags & FOLL_WRITE) &&
!can_follow_write_pte(pte, page, vma, flags)) {
page = NULL;
goto out;
}
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) {
/*
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
* Only return device mapping pages in the FOLL_GET or FOLL_PIN
* case since they are only valid while holding the pgmap
* reference.
*/
*pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
if (*pgmap)
page = pte_page(pte);
else
goto no_page;
} else if (unlikely(!page)) {
if (flags & FOLL_DUMP) {
/* Avoid special (like zero) pages in core dumps */
page = ERR_PTR(-EFAULT);
goto out;
}
if (is_zero_pfn(pte_pfn(pte))) {
page = pte_page(pte);
} else {
ret = follow_pfn_pte(vma, address, ptep, flags);
page = ERR_PTR(ret);
goto out;
}
}
mm/gup: reliable R/O long-term pinning in COW mappings We already support reliable R/O pinning of anonymous memory. However, assume we end up pinning (R/O long-term) a pagecache page or the shared zeropage inside a writable private ("COW") mapping. The next write access will trigger a write-fault and replace the pinned page by an exclusive anonymous page in the process page tables to break COW: the pinned page no longer corresponds to the page mapped into the process' page table. Now that FAULT_FLAG_UNSHARE can break COW on anything mapped into a COW mapping, let's properly break COW first before R/O long-term pinning something that's not an exclusive anon page inside a COW mapping. FAULT_FLAG_UNSHARE will break COW and map an exclusive anon page instead that can get pinned safely. With this change, we can stop using FOLL_FORCE|FOLL_WRITE for reliable R/O long-term pinning in COW mappings. With this change, the new R/O long-term pinning tests for non-anonymous memory succeed: # [RUN] R/O longterm GUP pin ... with shared zeropage ok 151 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd ok 152 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with tmpfile ok 153 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with huge zeropage ok 154 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (2048 kB) ok 155 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (1048576 kB) ok 156 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with shared zeropage ok 157 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd ok 158 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with tmpfile ok 159 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with huge zeropage ok 160 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (2048 kB) ok 161 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (1048576 kB) ok 162 Longterm R/O pin is reliable Note 1: We don't care about short-term R/O-pinning, because they have snapshot semantics: they are not supposed to observe modifications that happen after pinning. As one example, assume we start direct I/O to read from a page and store page content into a file: modifications to page content after starting direct I/O are not guaranteed to end up in the file. So even if we'd pin the shared zeropage, the end result would be as expected -- getting zeroes stored to the file. Note 2: For shared mappings we'll now always fallback to the slow path to lookup the VMA when R/O long-term pining. While that's the necessary price we have to pay right now, it's actually not that bad in practice: most FOLL_LONGTERM users already specify FOLL_WRITE, for example, along with FOLL_FORCE because they tried dealing with COW mappings correctly ... Note 3: For users that use FOLL_LONGTERM right now without FOLL_WRITE, such as VFIO, we'd now no longer pin the shared zeropage. Instead, we'd populate exclusive anon pages that we can pin. There was a concern that this could affect the memlock limit of existing setups. For example, a VM running with VFIO could run into the memlock limit and fail to run. However, we essentially had the same behavior already in commit 17839856fd58 ("gup: document and work around "COW can break either way" issue") which got merged into some enterprise distros, and there were not any such complaints. So most probably, we're fine. Link: https://lkml.kernel.org/r/20221116102659.70287-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-16 18:26:48 +08:00
if (!pte_write(pte) && gup_must_unshare(vma, flags, page)) {
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
page = ERR_PTR(-EMLINK);
goto out;
}
mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Let's verify when (un)pinning anonymous pages that we always deal with exclusive anonymous pages, which guarantees that we'll have a reliable PIN, meaning that we cannot end up with the GUP pin being inconsistent with he pages mapped into the page tables due to a COW triggered by a write fault. When pinning pages, after conditionally triggering GUP unsharing of possibly shared anonymous pages, we should always only see exclusive anonymous pages. Note that anonymous pages that are mapped writable must be marked exclusive, otherwise we'd have a BUG. When pinning during ordinary GUP, simply add a check after our conditional GUP-triggered unsharing checks. As we know exactly how the page is mapped, we know exactly in which page we have to check for PageAnonExclusive(). When pinning via GUP-fast we have to be careful, because we can race with fork(): verify only after we made sure via the seqcount that we didn't race with concurrent fork() that we didn't end up pinning a possibly shared anonymous page. Similarly, when unpinning, verify that the pages are still marked as exclusive: otherwise something turned the pages possibly shared, which can result in random memory corruptions, which we really want to catch. With only the pinned pages at hand and not the actual page table entries we have to be a bit careful: hugetlb pages are always mapped via a single logical page table entry referencing the head page and PG_anon_exclusive of the head page applies. Anon THP are a bit more complicated, because we might have obtained the page reference either via a PMD or a PTE -- depending on the mapping type we either have to check PageAnonExclusive of the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies: as we don't know and to make our life easier, check that either is set. Take care to not verify in case we're unpinning during GUP-fast because we detected concurrent fork(): we might stumble over an anonymous page that is now shared. Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
!PageAnonExclusive(page), page);
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
/* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */
ret = try_grab_page(page, flags);
if (unlikely(ret)) {
page = ERR_PTR(ret);
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
goto out;
}
mm/gup/writeback: add callbacks for inaccessible pages With the introduction of protected KVM guests on s390 there is now a concept of inaccessible pages. These pages need to be made accessible before the host can access them. While cpu accesses will trigger a fault that can be resolved, I/O accesses will just fail. We need to add a callback into architecture code for places that will do I/O, namely when writeback is started or when a page reference is taken. This is not only to enable paging, file backing etc, it is also necessary to protect the host against a malicious user space. For example a bad QEMU could simply start direct I/O on such protected memory. We do not want userspace to be able to trigger I/O errors and thus the logic is "whenever somebody accesses that page (gup) or does I/O, make sure that this page can be accessed". When the guest tries to access that page we will wait in the page fault handler for writeback to have finished and for the page_ref to be the expected value. On s390x the function is not supposed to fail, so it is ok to use a WARN_ON on failure. If we ever need some more finegrained handling we can tackle this when we know the details. Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Acked-by: Will Deacon <will@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Matthew Wilcox <willy@infradead.org> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200306132537.783769-3-imbrenda@linux.ibm.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:56 +08:00
/*
* We need to make the page accessible if and only if we are going
* to access its content (the FOLL_PIN case). Please see
* Documentation/core-api/pin_user_pages.rst for details.
*/
if (flags & FOLL_PIN) {
ret = arch_make_page_accessible(page);
if (ret) {
unpin_user_page(page);
page = ERR_PTR(ret);
goto out;
}
}
if (flags & FOLL_TOUCH) {
if ((flags & FOLL_WRITE) &&
!pte_dirty(pte) && !PageDirty(page))
set_page_dirty(page);
/*
* pte_mkyoung() would be more correct here, but atomic care
* is needed to avoid losing the dirty bit: it is easier to use
* mark_page_accessed().
*/
mark_page_accessed(page);
}
out:
pte_unmap_unlock(ptep, ptl);
return page;
no_page:
pte_unmap_unlock(ptep, ptl);
if (!pte_none(pte))
return NULL;
return no_page_table(vma, flags);
}
static struct page *follow_pmd_mask(struct vm_area_struct *vma,
unsigned long address, pud_t *pudp,
unsigned int flags,
struct follow_page_context *ctx)
{
pmd_t *pmd, pmdval;
spinlock_t *ptl;
struct page *page;
struct mm_struct *mm = vma->vm_mm;
pmd = pmd_offset(pudp, address);
/*
* The READ_ONCE() will stabilize the pmdval in a register or
* on the stack so that it will stop changing under the code.
*/
pmdval = READ_ONCE(*pmd);
if (pmd_none(pmdval))
return no_page_table(vma, flags);
if (!pmd_present(pmdval))
mm/hugetlb: take page table lock in follow_huge_pmd() We have a race condition between move_pages() and freeing hugepages, where move_pages() calls follow_page(FOLL_GET) for hugepages internally and tries to get its refcount without preventing concurrent freeing. This race crashes the kernel, so this patch fixes it by moving FOLL_GET code for hugepages into follow_huge_pmd() with taking the page table lock. This patch intentionally removes page==NULL check after pte_page. This is justified because pte_page() never returns NULL for any architectures or configurations. This patch changes the behavior of follow_huge_pmd() for tail pages and then tail pages can be pinned/returned. So the caller must be changed to properly handle the returned tail pages. We could have a choice to add the similar locking to follow_huge_(addr|pud) for consistency, but it's not necessary because currently these functions don't support FOLL_GET flag, so let's leave it for future development. Here is the reproducer: $ cat movepages.c #include <stdio.h> #include <stdlib.h> #include <numaif.h> #define ADDR_INPUT 0x700000000000UL #define HPS 0x200000 #define PS 0x1000 int main(int argc, char *argv[]) { int i; int nr_hp = strtol(argv[1], NULL, 0); int nr_p = nr_hp * HPS / PS; int ret; void **addrs; int *status; int *nodes; pid_t pid; pid = strtol(argv[2], NULL, 0); addrs = malloc(sizeof(char *) * nr_p + 1); status = malloc(sizeof(char *) * nr_p + 1); nodes = malloc(sizeof(char *) * nr_p + 1); while (1) { for (i = 0; i < nr_p; i++) { addrs[i] = (void *)ADDR_INPUT + i * PS; nodes[i] = 1; status[i] = 0; } ret = numa_move_pages(pid, nr_p, addrs, nodes, status, MPOL_MF_MOVE_ALL); if (ret == -1) err("move_pages"); for (i = 0; i < nr_p; i++) { addrs[i] = (void *)ADDR_INPUT + i * PS; nodes[i] = 0; status[i] = 0; } ret = numa_move_pages(pid, nr_p, addrs, nodes, status, MPOL_MF_MOVE_ALL); if (ret == -1) err("move_pages"); } return 0; } $ cat hugepage.c #include <stdio.h> #include <sys/mman.h> #include <string.h> #define ADDR_INPUT 0x700000000000UL #define HPS 0x200000 int main(int argc, char *argv[]) { int nr_hp = strtol(argv[1], NULL, 0); char *p; while (1) { p = mmap((void *)ADDR_INPUT, nr_hp * HPS, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0); if (p != (void *)ADDR_INPUT) { perror("mmap"); break; } memset(p, 0, nr_hp * HPS); munmap(p, nr_hp * HPS); } } $ sysctl vm.nr_hugepages=40 $ ./hugepage 10 & $ ./movepages 10 $(pgrep -f hugepage) Fixes: e632a938d914 ("mm: migrate: add hugepage migration code to move_pages()") Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Reported-by: Hugh Dickins <hughd@google.com> Cc: James Hogan <james.hogan@imgtec.com> Cc: David Rientjes <rientjes@google.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Rik van Riel <riel@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Luiz Capitulino <lcapitulino@redhat.com> Cc: Nishanth Aravamudan <nacc@linux.vnet.ibm.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Steve Capper <steve.capper@linaro.org> Cc: <stable@vger.kernel.org> [3.12+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:25:22 +08:00
return no_page_table(vma, flags);
if (pmd_devmap(pmdval)) {
ptl = pmd_lock(mm, pmd);
page = follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap);
spin_unlock(ptl);
if (page)
return page;
}
if (likely(!pmd_trans_huge(pmdval)))
return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
if (pmd_protnone(pmdval) && !gup_can_follow_protnone(flags))
return no_page_table(vma, flags);
ptl = pmd_lock(mm, pmd);
mm: thp: check pmd migration entry in common path When THP migration is being used, memory management code needs to handle pmd migration entries properly. This patch uses !pmd_present() or is_swap_pmd() (depending on whether pmd_none() needs separate code or not) to check pmd migration entries at the places where a pmd entry is present. Since pmd-related code uses split_huge_page(), split_huge_pmd(), pmd_trans_huge(), pmd_trans_unstable(), or pmd_none_or_trans_huge_or_clear_bad(), this patch: 1. adds pmd migration entry split code in split_huge_pmd(), 2. takes care of pmd migration entries whenever pmd_trans_huge() is present, 3. makes pmd_none_or_trans_huge_or_clear_bad() pmd migration entry aware. Since split_huge_page() uses split_huge_pmd() and pmd_trans_unstable() is equivalent to pmd_none_or_trans_huge_or_clear_bad(), we do not change them. Until this commit, a pmd entry should be: 1. pointing to a pte page, 2. is_swap_pmd(), 3. pmd_trans_huge(), 4. pmd_devmap(), or 5. pmd_none(). Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: David Nellans <dnellans@nvidia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Minchan Kim <minchan@kernel.org> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-09 07:11:01 +08:00
if (unlikely(!pmd_present(*pmd))) {
spin_unlock(ptl);
return no_page_table(vma, flags);
mm: thp: check pmd migration entry in common path When THP migration is being used, memory management code needs to handle pmd migration entries properly. This patch uses !pmd_present() or is_swap_pmd() (depending on whether pmd_none() needs separate code or not) to check pmd migration entries at the places where a pmd entry is present. Since pmd-related code uses split_huge_page(), split_huge_pmd(), pmd_trans_huge(), pmd_trans_unstable(), or pmd_none_or_trans_huge_or_clear_bad(), this patch: 1. adds pmd migration entry split code in split_huge_pmd(), 2. takes care of pmd migration entries whenever pmd_trans_huge() is present, 3. makes pmd_none_or_trans_huge_or_clear_bad() pmd migration entry aware. Since split_huge_page() uses split_huge_pmd() and pmd_trans_unstable() is equivalent to pmd_none_or_trans_huge_or_clear_bad(), we do not change them. Until this commit, a pmd entry should be: 1. pointing to a pte page, 2. is_swap_pmd(), 3. pmd_trans_huge(), 4. pmd_devmap(), or 5. pmd_none(). Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: David Nellans <dnellans@nvidia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Minchan Kim <minchan@kernel.org> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-09 07:11:01 +08:00
}
if (unlikely(!pmd_trans_huge(*pmd))) {
spin_unlock(ptl);
return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
}
if (flags & FOLL_SPLIT_PMD) {
int ret;
page = pmd_page(*pmd);
if (is_huge_zero_page(page)) {
spin_unlock(ptl);
ret = 0;
split_huge_pmd(vma, pmd, address);
if (pmd_trans_unstable(pmd))
ret = -EBUSY;
} else {
spin_unlock(ptl);
split_huge_pmd(vma, pmd, address);
ret = pte_alloc(mm, pmd) ? -ENOMEM : 0;
}
return ret ? ERR_PTR(ret) :
follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
}
page = follow_trans_huge_pmd(vma, address, pmd, flags);
spin_unlock(ptl);
ctx->page_mask = HPAGE_PMD_NR - 1;
return page;
}
static struct page *follow_pud_mask(struct vm_area_struct *vma,
unsigned long address, p4d_t *p4dp,
unsigned int flags,
struct follow_page_context *ctx)
{
pud_t *pud;
spinlock_t *ptl;
struct page *page;
struct mm_struct *mm = vma->vm_mm;
pud = pud_offset(p4dp, address);
if (pud_none(*pud))
return no_page_table(vma, flags);
if (pud_devmap(*pud)) {
ptl = pud_lock(mm, pud);
page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap);
spin_unlock(ptl);
if (page)
return page;
}
if (unlikely(pud_bad(*pud)))
return no_page_table(vma, flags);
return follow_pmd_mask(vma, address, pud, flags, ctx);
}
static struct page *follow_p4d_mask(struct vm_area_struct *vma,
unsigned long address, pgd_t *pgdp,
unsigned int flags,
struct follow_page_context *ctx)
{
p4d_t *p4d;
p4d = p4d_offset(pgdp, address);
if (p4d_none(*p4d))
return no_page_table(vma, flags);
BUILD_BUG_ON(p4d_huge(*p4d));
if (unlikely(p4d_bad(*p4d)))
return no_page_table(vma, flags);
return follow_pud_mask(vma, address, p4d, flags, ctx);
}
/**
* follow_page_mask - look up a page descriptor from a user-virtual address
* @vma: vm_area_struct mapping @address
* @address: virtual address to look up
* @flags: flags modifying lookup behaviour
* @ctx: contains dev_pagemap for %ZONE_DEVICE memory pinning and a
* pointer to output page_mask
*
* @flags can have FOLL_ flags set, defined in <linux/mm.h>
*
* When getting pages from ZONE_DEVICE memory, the @ctx->pgmap caches
* the device's dev_pagemap metadata to avoid repeating expensive lookups.
*
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
* When getting an anonymous page and the caller has to trigger unsharing
* of a shared anonymous page first, -EMLINK is returned. The caller should
* trigger a fault with FAULT_FLAG_UNSHARE set. Note that unsharing is only
* relevant with FOLL_PIN and !FOLL_WRITE.
*
* On output, the @ctx->page_mask is set according to the size of the page.
*
* Return: the mapped (struct page *), %NULL if no mapping exists, or
* an error pointer if there is a mapping to something not represented
* by a page descriptor (see also vm_normal_page()).
*/
static struct page *follow_page_mask(struct vm_area_struct *vma,
unsigned long address, unsigned int flags,
struct follow_page_context *ctx)
{
pgd_t *pgd;
struct page *page;
struct mm_struct *mm = vma->vm_mm;
ctx->page_mask = 0;
hugetlb: simplify hugetlb handling in follow_page_mask During discussions of this series [1], it was suggested that hugetlb handling code in follow_page_mask could be simplified. At the beginning of follow_page_mask, there currently is a call to follow_huge_addr which 'may' handle hugetlb pages. ia64 is the only architecture which provides a follow_huge_addr routine that does not return error. Instead, at each level of the page table a check is made for a hugetlb entry. If a hugetlb entry is found, a call to a routine associated with that entry is made. Currently, there are two checks for hugetlb entries at each page table level. The first check is of the form: if (p?d_huge()) page = follow_huge_p?d(); the second check is of the form: if (is_hugepd()) page = follow_huge_pd(). We can replace these checks, as well as the special handling routines such as follow_huge_p?d() and follow_huge_pd() with a single routine to handle hugetlb vmas. A new routine hugetlb_follow_page_mask is called for hugetlb vmas at the beginning of follow_page_mask. hugetlb_follow_page_mask will use the existing routine huge_pte_offset to walk page tables looking for hugetlb entries. huge_pte_offset can be overwritten by architectures, and already handles special cases such as hugepd entries. [1] https://lore.kernel.org/linux-mm/cover.1661240170.git.baolin.wang@linux.alibaba.com/ [mike.kravetz@oracle.com: remove vma (pmd sharing) per Peter] Link: https://lkml.kernel.org/r/20221028181108.119432-1-mike.kravetz@oracle.com [mike.kravetz@oracle.com: remove left over hugetlb_vma_unlock_read()] Link: https://lkml.kernel.org/r/20221030225825.40872-1-mike.kravetz@oracle.com Link: https://lkml.kernel.org/r/20220919021348.22151-1-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> Suggested-by: David Hildenbrand <david@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Muchun Song <songmuchun@bytedance.com> Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-09-19 10:13:48 +08:00
/*
* Call hugetlb_follow_page_mask for hugetlb vmas as it will use
* special hugetlb page table walking code. This eliminates the
* need to check for hugetlb entries in the general walking code.
*
* hugetlb_follow_page_mask is only for follow_page() handling here.
* Ordinary GUP uses follow_hugetlb_page for hugetlb processing.
*/
if (is_vm_hugetlb_page(vma)) {
page = hugetlb_follow_page_mask(vma, address, flags);
if (!page)
page = no_page_table(vma, flags);
return page;
}
pgd = pgd_offset(mm, address);
if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
return no_page_table(vma, flags);
return follow_p4d_mask(vma, address, pgd, flags, ctx);
}
struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
unsigned int foll_flags)
{
struct follow_page_context ctx = { NULL };
struct page *page;
mm: introduce memfd_secret system call to create "secret" memory areas Introduce "memfd_secret" system call with the ability to create memory areas visible only in the context of the owning process and not mapped not only to other processes but in the kernel page tables as well. The secretmem feature is off by default and the user must explicitly enable it at the boot time. Once secretmem is enabled, the user will be able to create a file descriptor using the memfd_secret() system call. The memory areas created by mmap() calls from this file descriptor will be unmapped from the kernel direct map and they will be only mapped in the page table of the processes that have access to the file descriptor. Secretmem is designed to provide the following protections: * Enhanced protection (in conjunction with all the other in-kernel attack prevention systems) against ROP attacks. Seceretmem makes "simple" ROP insufficient to perform exfiltration, which increases the required complexity of the attack. Along with other protections like the kernel stack size limit and address space layout randomization which make finding gadgets is really hard, absence of any in-kernel primitive for accessing secret memory means the one gadget ROP attack can't work. Since the only way to access secret memory is to reconstruct the missing mapping entry, the attacker has to recover the physical page and insert a PTE pointing to it in the kernel and then retrieve the contents. That takes at least three gadgets which is a level of difficulty beyond most standard attacks. * Prevent cross-process secret userspace memory exposures. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere. The secreremem pages cannot be accessed via the direct map and they are disallowed in GUP. * Harden against exploited kernel flaws. In order to access secretmem, a kernel-side attack would need to either walk the page tables and create new ones, or spawn a new privileged uiserspace process to perform secrets exfiltration using ptrace. The file descriptor based memory has several advantages over the "traditional" mm interfaces, such as mlock(), mprotect(), madvise(). File descriptor approach allows explicit and controlled sharing of the memory areas, it allows to seal the operations. Besides, file descriptor based memory paves the way for VMMs to remove the secret memory range from the userspace hipervisor process, for instance QEMU. Andy Lutomirski says: "Getting fd-backed memory into a guest will take some possibly major work in the kernel, but getting vma-backed memory into a guest without mapping it in the host user address space seems much, much worse." memfd_secret() is made a dedicated system call rather than an extension to memfd_create() because it's purpose is to allow the user to create more secure memory mappings rather than to simply allow file based access to the memory. Nowadays a new system call cost is negligible while it is way simpler for userspace to deal with a clear-cut system calls than with a multiplexer or an overloaded syscall. Moreover, the initial implementation of memfd_secret() is completely distinct from memfd_create() so there is no much sense in overloading memfd_create() to begin with. If there will be a need for code sharing between these implementation it can be easily achieved without a need to adjust user visible APIs. The secret memory remains accessible in the process context using uaccess primitives, but it is not exposed to the kernel otherwise; secret memory areas are removed from the direct map and functions in the follow_page()/get_user_page() family will refuse to return a page that belongs to the secret memory area. Once there will be a use case that will require exposing secretmem to the kernel it will be an opt-in request in the system call flags so that user would have to decide what data can be exposed to the kernel. Removing of the pages from the direct map may cause its fragmentation on architectures that use large pages to map the physical memory which affects the system performance. However, the original Kconfig text for CONFIG_DIRECT_GBPAGES said that gigabyte pages in the direct map "... can improve the kernel's performance a tiny bit ..." (commit 00d1c5e05736 ("x86: add gbpages switches")) and the recent report [1] showed that "... although 1G mappings are a good default choice, there is no compelling evidence that it must be the only choice". Hence, it is sufficient to have secretmem disabled by default with the ability of a system administrator to enable it at boot time. Pages in the secretmem regions are unevictable and unmovable to avoid accidental exposure of the sensitive data via swap or during page migration. Since the secretmem mappings are locked in memory they cannot exceed RLIMIT_MEMLOCK. Since these mappings are already locked independently from mlock(), an attempt to mlock()/munlock() secretmem range would fail and mlockall()/munlockall() will ignore secretmem mappings. However, unlike mlock()ed memory, secretmem currently behaves more like long-term GUP: secretmem mappings are unmovable mappings directly consumed by user space. With default limits, there is no excessive use of secretmem and it poses no real problem in combination with ZONE_MOVABLE/CMA, but in the future this should be addressed to allow balanced use of large amounts of secretmem along with ZONE_MOVABLE/CMA. A page that was a part of the secret memory area is cleared when it is freed to ensure the data is not exposed to the next user of that page. The following example demonstrates creation of a secret mapping (error handling is omitted): fd = memfd_secret(0); ftruncate(fd, MAP_SIZE); ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); [1] https://lore.kernel.org/linux-mm/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux.intel.com/ [akpm@linux-foundation.org: suppress Kconfig whine] Link: https://lkml.kernel.org/r/20210518072034.31572-5-rppt@kernel.org Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: Hagen Paul Pfeifer <hagen@jauu.net> Acked-by: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christopher Lameter <cl@linux.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Bottomley <jejb@linux.ibm.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Palmer Dabbelt <palmerdabbelt@google.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tycho Andersen <tycho@tycho.ws> Cc: Will Deacon <will@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: kernel test robot <lkp@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-08 09:08:03 +08:00
if (vma_is_secretmem(vma))
return NULL;
if (WARN_ON_ONCE(foll_flags & FOLL_PIN))
mm/gup: disallow follow_page(FOLL_PIN) We want to change the way we handle R/O pins on anonymous pages that might be shared: if we detect a possibly shared anonymous page -- mapped R/O and not !PageAnonExclusive() -- we want to trigger unsharing via a page fault, resulting in an exclusive anonymous page that can be pinned reliably without getting replaced via COW on the next write fault. However, the required page fault will be problematic for follow_page(): in contrast to ordinary GUP, follow_page() doesn't trigger faults internally. So we would have to end up failing a R/O pin via follow_page(), although there is something mapped R/O into the page table, which might be rather surprising. We don't seem to have follow_page(FOLL_PIN) users, and it's a purely internal MM function. Let's just make our life easier and the semantics of follow_page() clearer by just disallowing FOLL_PIN for follow_page() completely. Link: https://lkml.kernel.org/r/20220428083441.37290-15-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:44 +08:00
return NULL;
page = follow_page_mask(vma, address, foll_flags, &ctx);
if (ctx.pgmap)
put_dev_pagemap(ctx.pgmap);
return page;
}
static int get_gate_page(struct mm_struct *mm, unsigned long address,
unsigned int gup_flags, struct vm_area_struct **vma,
struct page **page)
{
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
int ret = -EFAULT;
/* user gate pages are read-only */
if (gup_flags & FOLL_WRITE)
return -EFAULT;
if (address > TASK_SIZE)
pgd = pgd_offset_k(address);
else
pgd = pgd_offset_gate(mm, address);
if (pgd_none(*pgd))
return -EFAULT;
p4d = p4d_offset(pgd, address);
if (p4d_none(*p4d))
return -EFAULT;
pud = pud_offset(p4d, address);
if (pud_none(*pud))
return -EFAULT;
pmd = pmd_offset(pud, address);
mm: thp: check pmd migration entry in common path When THP migration is being used, memory management code needs to handle pmd migration entries properly. This patch uses !pmd_present() or is_swap_pmd() (depending on whether pmd_none() needs separate code or not) to check pmd migration entries at the places where a pmd entry is present. Since pmd-related code uses split_huge_page(), split_huge_pmd(), pmd_trans_huge(), pmd_trans_unstable(), or pmd_none_or_trans_huge_or_clear_bad(), this patch: 1. adds pmd migration entry split code in split_huge_pmd(), 2. takes care of pmd migration entries whenever pmd_trans_huge() is present, 3. makes pmd_none_or_trans_huge_or_clear_bad() pmd migration entry aware. Since split_huge_page() uses split_huge_pmd() and pmd_trans_unstable() is equivalent to pmd_none_or_trans_huge_or_clear_bad(), we do not change them. Until this commit, a pmd entry should be: 1. pointing to a pte page, 2. is_swap_pmd(), 3. pmd_trans_huge(), 4. pmd_devmap(), or 5. pmd_none(). Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: David Nellans <dnellans@nvidia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Minchan Kim <minchan@kernel.org> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-09 07:11:01 +08:00
if (!pmd_present(*pmd))
return -EFAULT;
VM_BUG_ON(pmd_trans_huge(*pmd));
pte = pte_offset_map(pmd, address);
if (pte_none(*pte))
goto unmap;
*vma = get_gate_vma(mm);
if (!page)
goto out;
*page = vm_normal_page(*vma, address, *pte);
if (!*page) {
if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
goto unmap;
*page = pte_page(*pte);
}
ret = try_grab_page(*page, gup_flags);
if (unlikely(ret))
goto unmap;
out:
ret = 0;
unmap:
pte_unmap(pte);
return ret;
}
/*
* mmap_lock must be held on entry. If @flags has FOLL_UNLOCKABLE but not
* FOLL_NOWAIT, the mmap_lock may be released. If it is, *@locked will be set
* to 0 and -EBUSY returned.
*/
static int faultin_page(struct vm_area_struct *vma,
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
unsigned long address, unsigned int *flags, bool unshare,
int *locked)
{
unsigned int fault_flags = 0;
vm_fault_t ret;
if (*flags & FOLL_NOFAULT)
return -EFAULT;
if (*flags & FOLL_WRITE)
fault_flags |= FAULT_FLAG_WRITE;
mm/core: Do not enforce PKEY permissions on remote mm access We try to enforce protection keys in software the same way that we do in hardware. (See long example below). But, we only want to do this when accessing our *own* process's memory. If GDB set PKRU[6].AD=1 (disable access to PKEY 6), then tried to PTRACE_POKE a target process which just happened to have some mprotect_pkey(pkey=6) memory, we do *not* want to deny the debugger access to that memory. PKRU is fundamentally a thread-local structure and we do not want to enforce it on access to _another_ thread's data. This gets especially tricky when we have workqueues or other delayed-work mechanisms that might run in a random process's context. We can check that we only enforce pkeys when operating on our *own* mm, but delayed work gets performed when a random user context is active. We might end up with a situation where a delayed-work gup fails when running randomly under its "own" task but succeeds when running under another process. We want to avoid that. To avoid that, we use the new GUP flag: FOLL_REMOTE and add a fault flag: FAULT_FLAG_REMOTE. They indicate that we are walking an mm which is not guranteed to be the same as current->mm and should not be subject to protection key enforcement. Thanks to Jerome Glisse for pointing out this scenario. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <dchinner@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Geliang Tang <geliangtang@163.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Xie XiuQi <xiexiuqi@huawei.com> Cc: iommu@lists.linux-foundation.org Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:21 +08:00
if (*flags & FOLL_REMOTE)
fault_flags |= FAULT_FLAG_REMOTE;
if (*flags & FOLL_UNLOCKABLE) {
mm/gup: allow to react to fatal signals The existing gup code does not react to the fatal signals in many code paths. For example, in one retry path of gup we're still using down_read() rather than down_read_killable(). Also, when doing page faults we don't pass in FAULT_FLAG_KILLABLE as well, which means that within the faulting process we'll wait in non-killable way as well. These were spotted by Linus during the code review of some other patches. Let's allow the gup code to react to fatal signals to improve the responsiveness of threads when during gup and being killed. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: David Hildenbrand <david@redhat.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Martin Cracauer <cracauer@cons.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Matthew Wilcox <willy@infradead.org> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220160256.9887-1-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:08:53 +08:00
fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
mm/gup: Add FOLL_INTERRUPTIBLE We have had FAULT_FLAG_INTERRUPTIBLE but it was never applied to GUPs. One issue with it is that not all GUP paths are able to handle signal delivers besides SIGKILL. That's not ideal for the GUP users who are actually able to handle these cases, like KVM. KVM uses GUP extensively on faulting guest pages, during which we've got existing infrastructures to retry a page fault at a later time. Allowing the GUP to be interrupted by generic signals can make KVM related threads to be more responsive. For examples: (1) SIGUSR1: which QEMU/KVM uses to deliver an inter-process IPI, e.g. when the admin issues a vm_stop QMP command, SIGUSR1 can be generated to kick the vcpus out of kernel context immediately, (2) SIGINT: which can be used with interactive hypervisor users to stop a virtual machine with Ctrl-C without any delays/hangs, (3) SIGTRAP: which grants GDB capability even during page faults that are stuck for a long time. Normally hypervisor will be able to receive these signals properly, but not if we're stuck in a GUP for a long time for whatever reason. It happens easily with a stucked postcopy migration when e.g. a network temp failure happens, then some vcpu threads can hang death waiting for the pages. With the new FOLL_INTERRUPTIBLE, we can allow GUP users like KVM to selectively enable the ability to trap these signals. Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20221011195809.557016-2-peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2022-10-12 03:58:06 +08:00
/*
* FAULT_FLAG_INTERRUPTIBLE is opt-in. GUP callers must set
* FOLL_INTERRUPTIBLE to enable FAULT_FLAG_INTERRUPTIBLE.
* That's because some callers may not be prepared to
* handle early exits caused by non-fatal signals.
*/
if (*flags & FOLL_INTERRUPTIBLE)
fault_flags |= FAULT_FLAG_INTERRUPTIBLE;
}
if (*flags & FOLL_NOWAIT)
fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
if (*flags & FOLL_TRIED) {
/*
* Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
* can co-exist
*/
fault_flags |= FAULT_FLAG_TRIED;
}
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
if (unshare) {
fault_flags |= FAULT_FLAG_UNSHARE;
/* FAULT_FLAG_WRITE and FAULT_FLAG_UNSHARE are incompatible */
VM_BUG_ON(fault_flags & FAULT_FLAG_WRITE);
}
mm: do page fault accounting in handle_mm_fault Patch series "mm: Page fault accounting cleanups", v5. This is v5 of the pf accounting cleanup series. It originates from Gerald Schaefer's report on an issue a week ago regarding to incorrect page fault accountings for retried page fault after commit 4064b9827063 ("mm: allow VM_FAULT_RETRY for multiple times"): https://lore.kernel.org/lkml/20200610174811.44b94525@thinkpad/ What this series did: - Correct page fault accounting: we do accounting for a page fault (no matter whether it's from #PF handling, or gup, or anything else) only with the one that completed the fault. For example, page fault retries should not be counted in page fault counters. Same to the perf events. - Unify definition of PERF_COUNT_SW_PAGE_FAULTS: currently this perf event is used in an adhoc way across different archs. Case (1): for many archs it's done at the entry of a page fault handler, so that it will also cover e.g. errornous faults. Case (2): for some other archs, it is only accounted when the page fault is resolved successfully. Case (3): there're still quite some archs that have not enabled this perf event. Since this series will touch merely all the archs, we unify this perf event to always follow case (1), which is the one that makes most sense. And since we moved the accounting into handle_mm_fault, the other two MAJ/MIN perf events are well taken care of naturally. - Unify definition of "major faults": the definition of "major fault" is slightly changed when used in accounting (not VM_FAULT_MAJOR). More information in patch 1. - Always account the page fault onto the one that triggered the page fault. This does not matter much for #PF handlings, but mostly for gup. More information on this in patch 25. Patchset layout: Patch 1: Introduced the accounting in handle_mm_fault(), not enabled. Patch 2-23: Enable the new accounting for arch #PF handlers one by one. Patch 24: Enable the new accounting for the rest outliers (gup, iommu, etc.) Patch 25: Cleanup GUP task_struct pointer since it's not needed any more This patch (of 25): This is a preparation patch to move page fault accountings into the general code in handle_mm_fault(). This includes both the per task flt_maj/flt_min counters, and the major/minor page fault perf events. To do this, the pt_regs pointer is passed into handle_mm_fault(). PERF_COUNT_SW_PAGE_FAULTS should still be kept in per-arch page fault handlers. So far, all the pt_regs pointer that passed into handle_mm_fault() is NULL, which means this patch should have no intented functional change. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Cain <bcain@codeaurora.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Chris Zankel <chris@zankel.net> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David S. Miller <davem@davemloft.net> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com> Cc: Greentime Hu <green.hu@gmail.com> Cc: Guo Ren <guoren@kernel.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Helge Deller <deller@gmx.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jonas Bonn <jonas@southpole.se> Cc: Ley Foon Tan <ley.foon.tan@intel.com> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Matt Turner <mattst88@gmail.com> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Simek <monstr@monstr.eu> Cc: Nick Hu <nickhu@andestech.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Richard Henderson <rth@twiddle.net> Cc: Rich Felker <dalias@libc.org> Cc: Russell King <linux@armlinux.org.uk> Cc: Stafford Horne <shorne@gmail.com> Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Vincent Chen <deanbo422@gmail.com> Cc: Vineet Gupta <vgupta@synopsys.com> Cc: Will Deacon <will@kernel.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Link: http://lkml.kernel.org/r/20200707225021.200906-1-peterx@redhat.com Link: http://lkml.kernel.org/r/20200707225021.200906-2-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-08-12 09:37:44 +08:00
ret = handle_mm_fault(vma, address, fault_flags, NULL);
mm: avoid unnecessary page fault retires on shared memory types I observed that for each of the shared file-backed page faults, we're very likely to retry one more time for the 1st write fault upon no page. It's because we'll need to release the mmap lock for dirty rate limit purpose with balance_dirty_pages_ratelimited() (in fault_dirty_shared_page()). Then after that throttling we return VM_FAULT_RETRY. We did that probably because VM_FAULT_RETRY is the only way we can return to the fault handler at that time telling it we've released the mmap lock. However that's not ideal because it's very likely the fault does not need to be retried at all since the pgtable was well installed before the throttling, so the next continuous fault (including taking mmap read lock, walk the pgtable, etc.) could be in most cases unnecessary. It's not only slowing down page faults for shared file-backed, but also add more mmap lock contention which is in most cases not needed at all. To observe this, one could try to write to some shmem page and look at "pgfault" value in /proc/vmstat, then we should expect 2 counts for each shmem write simply because we retried, and vm event "pgfault" will capture that. To make it more efficient, add a new VM_FAULT_COMPLETED return code just to show that we've completed the whole fault and released the lock. It's also a hint that we should very possibly not need another fault immediately on this page because we've just completed it. This patch provides a ~12% perf boost on my aarch64 test VM with a simple program sequentially dirtying 400MB shmem file being mmap()ed and these are the time it needs: Before: 650.980 ms (+-1.94%) After: 569.396 ms (+-1.38%) I believe it could help more than that. We need some special care on GUP and the s390 pgfault handler (for gmap code before returning from pgfault), the rest changes in the page fault handlers should be relatively straightforward. Another thing to mention is that mm_account_fault() does take this new fault as a generic fault to be accounted, unlike VM_FAULT_RETRY. I explicitly didn't touch hmm_vma_fault() and break_ksm() because they do not handle VM_FAULT_RETRY even with existing code, so I'm literally keeping them as-is. Link: https://lkml.kernel.org/r/20220530183450.42886-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Vineet Gupta <vgupta@kernel.org> Acked-by: Guo Ren <guoren@kernel.org> Acked-by: Max Filippov <jcmvbkbc@gmail.com> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) Acked-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Alistair Popple <apopple@nvidia.com> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> [arm part] Acked-by: Heiko Carstens <hca@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Stafford Horne <shorne@gmail.com> Cc: David S. Miller <davem@davemloft.net> Cc: Johannes Berg <johannes@sipsolutions.net> Cc: Brian Cain <bcain@quicinc.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Richard Weinberger <richard@nod.at> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Janosch Frank <frankja@linux.ibm.com> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Jonas Bonn <jonas@southpole.se> Cc: Will Deacon <will@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Michal Simek <monstr@monstr.eu> Cc: Matt Turner <mattst88@gmail.com> Cc: Paul Mackerras <paulus@samba.org> Cc: David Hildenbrand <david@redhat.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Chris Zankel <chris@zankel.net> Cc: Hugh Dickins <hughd@google.com> Cc: Dinh Nguyen <dinguyen@kernel.org> Cc: Rich Felker <dalias@libc.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Helge Deller <deller@gmx.de> Cc: Yoshinori Sato <ysato@users.osdn.me> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-31 02:34:50 +08:00
if (ret & VM_FAULT_COMPLETED) {
/*
* With FAULT_FLAG_RETRY_NOWAIT we'll never release the
* mmap lock in the page fault handler. Sanity check this.
*/
WARN_ON_ONCE(fault_flags & FAULT_FLAG_RETRY_NOWAIT);
*locked = 0;
mm: avoid unnecessary page fault retires on shared memory types I observed that for each of the shared file-backed page faults, we're very likely to retry one more time for the 1st write fault upon no page. It's because we'll need to release the mmap lock for dirty rate limit purpose with balance_dirty_pages_ratelimited() (in fault_dirty_shared_page()). Then after that throttling we return VM_FAULT_RETRY. We did that probably because VM_FAULT_RETRY is the only way we can return to the fault handler at that time telling it we've released the mmap lock. However that's not ideal because it's very likely the fault does not need to be retried at all since the pgtable was well installed before the throttling, so the next continuous fault (including taking mmap read lock, walk the pgtable, etc.) could be in most cases unnecessary. It's not only slowing down page faults for shared file-backed, but also add more mmap lock contention which is in most cases not needed at all. To observe this, one could try to write to some shmem page and look at "pgfault" value in /proc/vmstat, then we should expect 2 counts for each shmem write simply because we retried, and vm event "pgfault" will capture that. To make it more efficient, add a new VM_FAULT_COMPLETED return code just to show that we've completed the whole fault and released the lock. It's also a hint that we should very possibly not need another fault immediately on this page because we've just completed it. This patch provides a ~12% perf boost on my aarch64 test VM with a simple program sequentially dirtying 400MB shmem file being mmap()ed and these are the time it needs: Before: 650.980 ms (+-1.94%) After: 569.396 ms (+-1.38%) I believe it could help more than that. We need some special care on GUP and the s390 pgfault handler (for gmap code before returning from pgfault), the rest changes in the page fault handlers should be relatively straightforward. Another thing to mention is that mm_account_fault() does take this new fault as a generic fault to be accounted, unlike VM_FAULT_RETRY. I explicitly didn't touch hmm_vma_fault() and break_ksm() because they do not handle VM_FAULT_RETRY even with existing code, so I'm literally keeping them as-is. Link: https://lkml.kernel.org/r/20220530183450.42886-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Vineet Gupta <vgupta@kernel.org> Acked-by: Guo Ren <guoren@kernel.org> Acked-by: Max Filippov <jcmvbkbc@gmail.com> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) Acked-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Alistair Popple <apopple@nvidia.com> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> [arm part] Acked-by: Heiko Carstens <hca@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Stafford Horne <shorne@gmail.com> Cc: David S. Miller <davem@davemloft.net> Cc: Johannes Berg <johannes@sipsolutions.net> Cc: Brian Cain <bcain@quicinc.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Richard Weinberger <richard@nod.at> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Janosch Frank <frankja@linux.ibm.com> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Jonas Bonn <jonas@southpole.se> Cc: Will Deacon <will@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Michal Simek <monstr@monstr.eu> Cc: Matt Turner <mattst88@gmail.com> Cc: Paul Mackerras <paulus@samba.org> Cc: David Hildenbrand <david@redhat.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Chris Zankel <chris@zankel.net> Cc: Hugh Dickins <hughd@google.com> Cc: Dinh Nguyen <dinguyen@kernel.org> Cc: Rich Felker <dalias@libc.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Helge Deller <deller@gmx.de> Cc: Yoshinori Sato <ysato@users.osdn.me> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-31 02:34:50 +08:00
/*
* We should do the same as VM_FAULT_RETRY, but let's not
* return -EBUSY since that's not reflecting the reality of
* what has happened - we've just fully completed a page
* fault, with the mmap lock released. Use -EAGAIN to show
* that we want to take the mmap lock _again_.
*/
return -EAGAIN;
}
if (ret & VM_FAULT_ERROR) {
mm/hugetlb: report -EHWPOISON not -EFAULT when FOLL_HWPOISON is specified KVM uses get_user_pages() to resolve its stage2 faults. KVM sets the FOLL_HWPOISON flag causing faultin_page() to return -EHWPOISON when it finds a VM_FAULT_HWPOISON. KVM handles these hwpoison pages as a special case. (check_user_page_hwpoison()) When huge pages are involved, this doesn't work so well. get_user_pages() calls follow_hugetlb_page(), which stops early if it receives VM_FAULT_HWPOISON from hugetlb_fault(), eventually returning -EFAULT to the caller. The step to map this to -EHWPOISON based on the FOLL_ flags is missing. The hwpoison special case is skipped, and -EFAULT is returned to user-space, causing Qemu or kvmtool to exit. Instead, move this VM_FAULT_ to errno mapping code into a header file and use it from faultin_page() and follow_hugetlb_page(). With this, KVM works as expected. This isn't a problem for arm64 today as we haven't enabled MEMORY_FAILURE, but I can't see any reason this doesn't happen on x86 too, so I think this should be a fix. This doesn't apply earlier than stable's v4.11.1 due to all sorts of cleanup. [james.morse@arm.com: add vm_fault_to_errno() call to faultin_page()] suggested. Link: http://lkml.kernel.org/r/20170525171035.16359-1-james.morse@arm.com [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20170524160900.28786-1-james.morse@arm.com Signed-off-by: James Morse <james.morse@arm.com> Acked-by: Punit Agrawal <punit.agrawal@arm.com> Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com> Cc: <stable@vger.kernel.org> [4.11.1+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-06-03 05:46:46 +08:00
int err = vm_fault_to_errno(ret, *flags);
if (err)
return err;
BUG();
}
if (ret & VM_FAULT_RETRY) {
if (!(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
mm/gup: rename "nonblocking" to "locked" where proper Patch series "mm: Page fault enhancements", v6. This series contains cleanups and enhancements to current page fault logic. The whole idea comes from the discussion between Andrea and Linus on the bug reported by syzbot here: https://lkml.org/lkml/2017/11/2/833 Basically it does two things: (a) Allows the page fault logic to be more interactive on not only SIGKILL, but also the rest of userspace signals, and, (b) Allows the page fault retry (VM_FAULT_RETRY) to happen for more than once. For (a): with the changes we should be able to react faster when page faults are working in parallel with userspace signals like SIGSTOP and SIGCONT (and more), and with that we can remove the buggy part in userfaultfd and benefit the whole page fault mechanism on faster signal processing to reach the userspace. For (b), we should be able to allow the page fault handler to loop for even more than twice. Some context: for now since we have FAULT_FLAG_ALLOW_RETRY we can allow to retry the page fault once with the same interrupt context, however never more than twice. This can be not only a potential cleanup to remove this assumption since AFAIU the code itself doesn't really have this twice-only limitation (though that should be a protective approach in the past), at the same time it'll greatly simplify future works like userfaultfd write-protect where it's possible to retry for more than twice (please have a look at [1] below for a possible user that might require the page fault to be handled for a third time; if we can remove the retry limitation we can simply drop that patch and those complexity). This patch (of 16): There's plenty of places around __get_user_pages() that has a parameter "nonblocking" which does not really mean that "it won't block" (because it can really block) but instead it shows whether the mmap_sem is released by up_read() during the page fault handling mostly when VM_FAULT_RETRY is returned. We have the correct naming in e.g. get_user_pages_locked() or get_user_pages_remote() as "locked", however there're still many places that are using the "nonblocking" as name. Renaming the places to "locked" where proper to better suite the functionality of the variable. While at it, fixing up some of the comments accordingly. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Martin Cracauer <cracauer@cons.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220155353.8676-2-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:07:58 +08:00
*locked = 0;
return -EBUSY;
}
return 0;
}
static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
{
vm_flags_t vm_flags = vma->vm_flags;
mm/core: Do not enforce PKEY permissions on remote mm access We try to enforce protection keys in software the same way that we do in hardware. (See long example below). But, we only want to do this when accessing our *own* process's memory. If GDB set PKRU[6].AD=1 (disable access to PKEY 6), then tried to PTRACE_POKE a target process which just happened to have some mprotect_pkey(pkey=6) memory, we do *not* want to deny the debugger access to that memory. PKRU is fundamentally a thread-local structure and we do not want to enforce it on access to _another_ thread's data. This gets especially tricky when we have workqueues or other delayed-work mechanisms that might run in a random process's context. We can check that we only enforce pkeys when operating on our *own* mm, but delayed work gets performed when a random user context is active. We might end up with a situation where a delayed-work gup fails when running randomly under its "own" task but succeeds when running under another process. We want to avoid that. To avoid that, we use the new GUP flag: FOLL_REMOTE and add a fault flag: FAULT_FLAG_REMOTE. They indicate that we are walking an mm which is not guranteed to be the same as current->mm and should not be subject to protection key enforcement. Thanks to Jerome Glisse for pointing out this scenario. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <dchinner@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Geliang Tang <geliangtang@163.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Xie XiuQi <xiexiuqi@huawei.com> Cc: iommu@lists.linux-foundation.org Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:21 +08:00
int write = (gup_flags & FOLL_WRITE);
int foreign = (gup_flags & FOLL_REMOTE);
if (vm_flags & (VM_IO | VM_PFNMAP))
return -EFAULT;
if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
return -EFAULT;
if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma))
return -EOPNOTSUPP;
mm: introduce memfd_secret system call to create "secret" memory areas Introduce "memfd_secret" system call with the ability to create memory areas visible only in the context of the owning process and not mapped not only to other processes but in the kernel page tables as well. The secretmem feature is off by default and the user must explicitly enable it at the boot time. Once secretmem is enabled, the user will be able to create a file descriptor using the memfd_secret() system call. The memory areas created by mmap() calls from this file descriptor will be unmapped from the kernel direct map and they will be only mapped in the page table of the processes that have access to the file descriptor. Secretmem is designed to provide the following protections: * Enhanced protection (in conjunction with all the other in-kernel attack prevention systems) against ROP attacks. Seceretmem makes "simple" ROP insufficient to perform exfiltration, which increases the required complexity of the attack. Along with other protections like the kernel stack size limit and address space layout randomization which make finding gadgets is really hard, absence of any in-kernel primitive for accessing secret memory means the one gadget ROP attack can't work. Since the only way to access secret memory is to reconstruct the missing mapping entry, the attacker has to recover the physical page and insert a PTE pointing to it in the kernel and then retrieve the contents. That takes at least three gadgets which is a level of difficulty beyond most standard attacks. * Prevent cross-process secret userspace memory exposures. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere. The secreremem pages cannot be accessed via the direct map and they are disallowed in GUP. * Harden against exploited kernel flaws. In order to access secretmem, a kernel-side attack would need to either walk the page tables and create new ones, or spawn a new privileged uiserspace process to perform secrets exfiltration using ptrace. The file descriptor based memory has several advantages over the "traditional" mm interfaces, such as mlock(), mprotect(), madvise(). File descriptor approach allows explicit and controlled sharing of the memory areas, it allows to seal the operations. Besides, file descriptor based memory paves the way for VMMs to remove the secret memory range from the userspace hipervisor process, for instance QEMU. Andy Lutomirski says: "Getting fd-backed memory into a guest will take some possibly major work in the kernel, but getting vma-backed memory into a guest without mapping it in the host user address space seems much, much worse." memfd_secret() is made a dedicated system call rather than an extension to memfd_create() because it's purpose is to allow the user to create more secure memory mappings rather than to simply allow file based access to the memory. Nowadays a new system call cost is negligible while it is way simpler for userspace to deal with a clear-cut system calls than with a multiplexer or an overloaded syscall. Moreover, the initial implementation of memfd_secret() is completely distinct from memfd_create() so there is no much sense in overloading memfd_create() to begin with. If there will be a need for code sharing between these implementation it can be easily achieved without a need to adjust user visible APIs. The secret memory remains accessible in the process context using uaccess primitives, but it is not exposed to the kernel otherwise; secret memory areas are removed from the direct map and functions in the follow_page()/get_user_page() family will refuse to return a page that belongs to the secret memory area. Once there will be a use case that will require exposing secretmem to the kernel it will be an opt-in request in the system call flags so that user would have to decide what data can be exposed to the kernel. Removing of the pages from the direct map may cause its fragmentation on architectures that use large pages to map the physical memory which affects the system performance. However, the original Kconfig text for CONFIG_DIRECT_GBPAGES said that gigabyte pages in the direct map "... can improve the kernel's performance a tiny bit ..." (commit 00d1c5e05736 ("x86: add gbpages switches")) and the recent report [1] showed that "... although 1G mappings are a good default choice, there is no compelling evidence that it must be the only choice". Hence, it is sufficient to have secretmem disabled by default with the ability of a system administrator to enable it at boot time. Pages in the secretmem regions are unevictable and unmovable to avoid accidental exposure of the sensitive data via swap or during page migration. Since the secretmem mappings are locked in memory they cannot exceed RLIMIT_MEMLOCK. Since these mappings are already locked independently from mlock(), an attempt to mlock()/munlock() secretmem range would fail and mlockall()/munlockall() will ignore secretmem mappings. However, unlike mlock()ed memory, secretmem currently behaves more like long-term GUP: secretmem mappings are unmovable mappings directly consumed by user space. With default limits, there is no excessive use of secretmem and it poses no real problem in combination with ZONE_MOVABLE/CMA, but in the future this should be addressed to allow balanced use of large amounts of secretmem along with ZONE_MOVABLE/CMA. A page that was a part of the secret memory area is cleared when it is freed to ensure the data is not exposed to the next user of that page. The following example demonstrates creation of a secret mapping (error handling is omitted): fd = memfd_secret(0); ftruncate(fd, MAP_SIZE); ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); [1] https://lore.kernel.org/linux-mm/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux.intel.com/ [akpm@linux-foundation.org: suppress Kconfig whine] Link: https://lkml.kernel.org/r/20210518072034.31572-5-rppt@kernel.org Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: Hagen Paul Pfeifer <hagen@jauu.net> Acked-by: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christopher Lameter <cl@linux.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Bottomley <jejb@linux.ibm.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Palmer Dabbelt <palmerdabbelt@google.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tycho Andersen <tycho@tycho.ws> Cc: Will Deacon <will@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: kernel test robot <lkp@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-08 09:08:03 +08:00
if (vma_is_secretmem(vma))
return -EFAULT;
mm/core: Do not enforce PKEY permissions on remote mm access We try to enforce protection keys in software the same way that we do in hardware. (See long example below). But, we only want to do this when accessing our *own* process's memory. If GDB set PKRU[6].AD=1 (disable access to PKEY 6), then tried to PTRACE_POKE a target process which just happened to have some mprotect_pkey(pkey=6) memory, we do *not* want to deny the debugger access to that memory. PKRU is fundamentally a thread-local structure and we do not want to enforce it on access to _another_ thread's data. This gets especially tricky when we have workqueues or other delayed-work mechanisms that might run in a random process's context. We can check that we only enforce pkeys when operating on our *own* mm, but delayed work gets performed when a random user context is active. We might end up with a situation where a delayed-work gup fails when running randomly under its "own" task but succeeds when running under another process. We want to avoid that. To avoid that, we use the new GUP flag: FOLL_REMOTE and add a fault flag: FAULT_FLAG_REMOTE. They indicate that we are walking an mm which is not guranteed to be the same as current->mm and should not be subject to protection key enforcement. Thanks to Jerome Glisse for pointing out this scenario. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <dchinner@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Geliang Tang <geliangtang@163.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Xie XiuQi <xiexiuqi@huawei.com> Cc: iommu@lists.linux-foundation.org Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:21 +08:00
if (write) {
if (!(vm_flags & VM_WRITE)) {
if (!(gup_flags & FOLL_FORCE))
return -EFAULT;
mm/gup: disallow FOLL_FORCE|FOLL_WRITE on hugetlb mappings hugetlb does not support fake write-faults (write faults without write permissions). However, we are currently able to trigger a FAULT_FLAG_WRITE fault on a VMA without VM_WRITE. If we'd ever want to support FOLL_FORCE|FOLL_WRITE, we'd have to teach hugetlb to: (1) Leave the page mapped R/O after the fake write-fault, like maybe_mkwrite() does. (2) Allow writing to an exclusive anon page that's mapped R/O when FOLL_FORCE is set, like can_follow_write_pte(). E.g., __follow_hugetlb_must_fault() needs adjustment. For now, it's not clear if that added complexity is really required. History tolds us that FOLL_FORCE is dangerous and that we better limit its use to a bare minimum. -------------------------------------------------------------------------- #include <stdio.h> #include <stdlib.h> #include <fcntl.h> #include <unistd.h> #include <errno.h> #include <stdint.h> #include <sys/mman.h> #include <linux/mman.h> int main(int argc, char **argv) { char *map; int mem_fd; map = mmap(NULL, 2 * 1024 * 1024u, PROT_READ, MAP_PRIVATE|MAP_ANON|MAP_HUGETLB|MAP_HUGE_2MB, -1, 0); if (map == MAP_FAILED) { fprintf(stderr, "mmap() failed: %d\n", errno); return 1; } mem_fd = open("/proc/self/mem", O_RDWR); if (mem_fd < 0) { fprintf(stderr, "open(/proc/self/mem) failed: %d\n", errno); return 1; } if (pwrite(mem_fd, "0", 1, (uintptr_t) map) == 1) { fprintf(stderr, "write() succeeded, which is unexpected\n"); return 1; } printf("write() failed as expected: %d\n", errno); return 0; } -------------------------------------------------------------------------- Fortunately, we have a sanity check in hugetlb_wp() in place ever since commit 1d8d14641fd9 ("mm/hugetlb: support write-faults in shared mappings"), that bails out instead of silently mapping a page writable in a !PROT_WRITE VMA. Consequently, above reproducer triggers a warning, similar to the one reported by szsbot: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 3612 at mm/hugetlb.c:5313 hugetlb_wp+0x20a/0x1af0 mm/hugetlb.c:5313 Modules linked in: CPU: 1 PID: 3612 Comm: syz-executor250 Not tainted 6.1.0-rc2-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022 RIP: 0010:hugetlb_wp+0x20a/0x1af0 mm/hugetlb.c:5313 Code: ea 03 80 3c 02 00 0f 85 31 14 00 00 49 8b 5f 20 31 ff 48 89 dd 83 e5 02 48 89 ee e8 70 ab b7 ff 48 85 ed 75 5b e8 76 ae b7 ff <0f> 0b 41 bd 40 00 00 00 e8 69 ae b7 ff 48 b8 00 00 00 00 00 fc ff RSP: 0018:ffffc90003caf620 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 0000000008640070 RCX: 0000000000000000 RDX: ffff88807b963a80 RSI: ffffffff81c4ed2a RDI: 0000000000000007 RBP: 0000000000000000 R08: 0000000000000007 R09: 0000000000000000 R10: 0000000000000000 R11: 000000000008c07e R12: ffff888023805800 R13: 0000000000000000 R14: ffffffff91217f38 R15: ffff88801d4b0360 FS: 0000555555bba300(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fff7a47a1b8 CR3: 000000002378d000 CR4: 00000000003506e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> hugetlb_no_page mm/hugetlb.c:5755 [inline] hugetlb_fault+0x19cc/0x2060 mm/hugetlb.c:5874 follow_hugetlb_page+0x3f3/0x1850 mm/hugetlb.c:6301 __get_user_pages+0x2cb/0xf10 mm/gup.c:1202 __get_user_pages_locked mm/gup.c:1434 [inline] __get_user_pages_remote+0x18f/0x830 mm/gup.c:2187 get_user_pages_remote+0x84/0xc0 mm/gup.c:2260 __access_remote_vm+0x287/0x6b0 mm/memory.c:5517 ptrace_access_vm+0x181/0x1d0 kernel/ptrace.c:61 generic_ptrace_pokedata kernel/ptrace.c:1323 [inline] ptrace_request+0xb46/0x10c0 kernel/ptrace.c:1046 arch_ptrace+0x36/0x510 arch/x86/kernel/ptrace.c:828 __do_sys_ptrace kernel/ptrace.c:1296 [inline] __se_sys_ptrace kernel/ptrace.c:1269 [inline] __x64_sys_ptrace+0x178/0x2a0 kernel/ptrace.c:1269 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd [...] So let's silence that warning by teaching GUP code that FOLL_FORCE -- so far -- does not apply to hugetlb. Note that FOLL_FORCE for read-access seems to be working as expected. The assumption is that this has been broken forever, only ever since above commit, we actually detect the wrong handling and WARN_ON_ONCE(). I assume this has been broken at least since 2014, when mm/gup.c came to life. I failed to come up with a suitable Fixes tag quickly. Link: https://lkml.kernel.org/r/20221031152524.173644-1-david@redhat.com Fixes: 1d8d14641fd9 ("mm/hugetlb: support write-faults in shared mappings") Signed-off-by: David Hildenbrand <david@redhat.com> Reported-by: <syzbot+f0b97304ef90f0d0b1dc@syzkaller.appspotmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-10-31 23:25:24 +08:00
/* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */
if (is_vm_hugetlb_page(vma))
return -EFAULT;
/*
* We used to let the write,force case do COW in a
* VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
* set a breakpoint in a read-only mapping of an
* executable, without corrupting the file (yet only
* when that file had been opened for writing!).
* Anon pages in shared mappings are surprising: now
* just reject it.
*/
if (!is_cow_mapping(vm_flags))
return -EFAULT;
}
} else if (!(vm_flags & VM_READ)) {
if (!(gup_flags & FOLL_FORCE))
return -EFAULT;
/*
* Is there actually any vma we can reach here which does not
* have VM_MAYREAD set?
*/
if (!(vm_flags & VM_MAYREAD))
return -EFAULT;
}
mm/core, x86/mm/pkeys: Differentiate instruction fetches As discussed earlier, we attempt to enforce protection keys in software. However, the code checks all faults to ensure that they are not violating protection key permissions. It was assumed that all faults are either write faults where we check PKRU[key].WD (write disable) or read faults where we check the AD (access disable) bit. But, there is a third category of faults for protection keys: instruction faults. Instruction faults never run afoul of protection keys because they do not affect instruction fetches. So, plumb the PF_INSTR bit down in to the arch_vma_access_permitted() function where we do the protection key checks. We also add a new FAULT_FLAG_INSTRUCTION. This is because handle_mm_fault() is not passed the architecture-specific error_code where we keep PF_INSTR, so we need to encode the instruction fetch information in to the arch-generic fault flags. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave@sr71.net> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20160212210224.96928009@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:24 +08:00
/*
* gups are always data accesses, not instruction
* fetches, so execute=false here
*/
if (!arch_vma_access_permitted(vma, write, false, foreign))
mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys Today, for normal faults and page table walks, we check the VMA and/or PTE to ensure that it is compatible with the action. For instance, if we get a write fault on a non-writeable VMA, we SIGSEGV. We try to do the same thing for protection keys. Basically, we try to make sure that if a user does this: mprotect(ptr, size, PROT_NONE); *ptr = foo; they see the same effects with protection keys when they do this: mprotect(ptr, size, PROT_READ|PROT_WRITE); set_pkey(ptr, size, 4); wrpkru(0xffffff3f); // access disable pkey 4 *ptr = foo; The state to do that checking is in the VMA, but we also sometimes have to do it on the page tables only, like when doing a get_user_pages_fast() where we have no VMA. We add two functions and expose them to generic code: arch_pte_access_permitted(pte_flags, write) arch_vma_access_permitted(vma, write) These are, of course, backed up in x86 arch code with checks against the PTE or VMA's protection key. But, there are also cases where we do not want to respect protection keys. When we ptrace(), for instance, we do not want to apply the tracer's PKRU permissions to the PTEs from the process being traced. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave@sr71.net> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: David Hildenbrand <dahi@linux.vnet.ibm.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20160212210219.14D5D715@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:19 +08:00
return -EFAULT;
return 0;
}
/**
* __get_user_pages() - pin user pages in memory
* @mm: mm_struct of target mm
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying pin behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long. Or NULL, if caller
* only intends to ensure the pages are faulted in.
* @vmas: array of pointers to vmas corresponding to each page.
* Or NULL if the caller does not require them.
* @locked: whether we're still with the mmap_lock held
*
* Returns either number of pages pinned (which may be less than the
* number requested), or an error. Details about the return value:
*
* -- If nr_pages is 0, returns 0.
* -- If nr_pages is >0, but no pages were pinned, returns -errno.
* -- If nr_pages is >0, and some pages were pinned, returns the number of
* pages pinned. Again, this may be less than nr_pages.
* -- 0 return value is possible when the fault would need to be retried.
*
* The caller is responsible for releasing returned @pages, via put_page().
*
* @vmas are valid only as long as mmap_lock is held.
*
* Must be called with mmap_lock held. It may be released. See below.
*
* __get_user_pages walks a process's page tables and takes a reference to
* each struct page that each user address corresponds to at a given
* instant. That is, it takes the page that would be accessed if a user
* thread accesses the given user virtual address at that instant.
*
* This does not guarantee that the page exists in the user mappings when
* __get_user_pages returns, and there may even be a completely different
* page there in some cases (eg. if mmapped pagecache has been invalidated
* and subsequently re-faulted). However it does guarantee that the page
* won't be freed completely. And mostly callers simply care that the page
* contains data that was valid *at some point in time*. Typically, an IO
* or similar operation cannot guarantee anything stronger anyway because
* locks can't be held over the syscall boundary.
*
* If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
* the page is written to, set_page_dirty (or set_page_dirty_lock, as
* appropriate) must be called after the page is finished with, and
* before put_page is called.
*
* If FOLL_UNLOCKABLE is set without FOLL_NOWAIT then the mmap_lock may
* be released. If this happens *@locked will be set to 0 on return.
*
* A caller using such a combination of @gup_flags must therefore hold the
* mmap_lock for reading only, and recognize when it's been released. Otherwise,
* it must be held for either reading or writing and will not be released.
*
* In most cases, get_user_pages or get_user_pages_fast should be used
* instead of __get_user_pages. __get_user_pages should be used only if
* you need some special @gup_flags.
*/
static long __get_user_pages(struct mm_struct *mm,
unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
mm/gup: rename "nonblocking" to "locked" where proper Patch series "mm: Page fault enhancements", v6. This series contains cleanups and enhancements to current page fault logic. The whole idea comes from the discussion between Andrea and Linus on the bug reported by syzbot here: https://lkml.org/lkml/2017/11/2/833 Basically it does two things: (a) Allows the page fault logic to be more interactive on not only SIGKILL, but also the rest of userspace signals, and, (b) Allows the page fault retry (VM_FAULT_RETRY) to happen for more than once. For (a): with the changes we should be able to react faster when page faults are working in parallel with userspace signals like SIGSTOP and SIGCONT (and more), and with that we can remove the buggy part in userfaultfd and benefit the whole page fault mechanism on faster signal processing to reach the userspace. For (b), we should be able to allow the page fault handler to loop for even more than twice. Some context: for now since we have FAULT_FLAG_ALLOW_RETRY we can allow to retry the page fault once with the same interrupt context, however never more than twice. This can be not only a potential cleanup to remove this assumption since AFAIU the code itself doesn't really have this twice-only limitation (though that should be a protective approach in the past), at the same time it'll greatly simplify future works like userfaultfd write-protect where it's possible to retry for more than twice (please have a look at [1] below for a possible user that might require the page fault to be handled for a third time; if we can remove the retry limitation we can simply drop that patch and those complexity). This patch (of 16): There's plenty of places around __get_user_pages() that has a parameter "nonblocking" which does not really mean that "it won't block" (because it can really block) but instead it shows whether the mmap_sem is released by up_read() during the page fault handling mostly when VM_FAULT_RETRY is returned. We have the correct naming in e.g. get_user_pages_locked() or get_user_pages_remote() as "locked", however there're still many places that are using the "nonblocking" as name. Renaming the places to "locked" where proper to better suite the functionality of the variable. While at it, fixing up some of the comments accordingly. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Martin Cracauer <cracauer@cons.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220155353.8676-2-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:07:58 +08:00
struct vm_area_struct **vmas, int *locked)
{
long ret = 0, i = 0;
struct vm_area_struct *vma = NULL;
struct follow_page_context ctx = { NULL };
if (!nr_pages)
return 0;
start = untagged_addr_remote(mm, start);
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
do {
struct page *page;
unsigned int foll_flags = gup_flags;
unsigned int page_increm;
/* first iteration or cross vma bound */
if (!vma || start >= vma->vm_end) {
vma = find_extend_vma(mm, start);
if (!vma && in_gate_area(mm, start)) {
ret = get_gate_page(mm, start & PAGE_MASK,
gup_flags, &vma,
pages ? &pages[i] : NULL);
if (ret)
mm/gup: finish consolidating error handling Commit df06b37ffe5a ("mm/gup: cache dev_pagemap while pinning pages") attempted to operate on each page that get_user_pages had retrieved. In order to do that, it created a common exit point from the routine. However, one case was missed, which this patch fixes up. Also, there was still an unnecessary shadow declaration (with a different type) of the "ret" variable, which this patch removes. Keith's description of the situation is: This also fixes a potentially leaked dev_pagemap reference count if a failure occurs when an iteration crosses a vma boundary. I don't think it's normal to have different vma's on a users mapped zone device memory, but good to fix anyway. I actually thought that this code: /* first iteration or cross vma bound */ if (!vma || start >= vma->vm_end) { vma = find_extend_vma(mm, start); if (!vma && in_gate_area(mm, start)) { ret = get_gate_page(mm, start & PAGE_MASK, gup_flags, &vma, pages ? &pages[i] : NULL); if (ret) goto out; dealt with the "you're trying to pin the gate page, as part of this call", rather than the generic case of crossing a vma boundary. (I think there's a fine point that I must be overlooking.) But it's still a valid case, either way. Link: http://lkml.kernel.org/r/20181121081402.29641-2-jhubbard@nvidia.com Fixes: df06b37ffe5a4 ("mm/gup: cache dev_pagemap while pinning pages") Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Keith Busch <keith.busch@intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-12-01 06:08:53 +08:00
goto out;
ctx.page_mask = 0;
goto next_page;
}
if (!vma) {
ret = -EFAULT;
goto out;
}
ret = check_vma_flags(vma, gup_flags);
if (ret)
goto out;
if (is_vm_hugetlb_page(vma)) {
i = follow_hugetlb_page(mm, vma, pages, vmas,
&start, &nr_pages, i,
gup_flags, locked);
if (!*locked) {
/*
* We've got a VM_FAULT_RETRY
* and we've lost mmap_lock.
* We must stop here.
*/
BUG_ON(gup_flags & FOLL_NOWAIT);
goto out;
}
continue;
}
}
retry:
/*
* If we have a pending SIGKILL, don't keep faulting pages and
* potentially allocating memory.
*/
if (fatal_signal_pending(current)) {
ret = -EINTR;
goto out;
}
cond_resched();
page = follow_page_mask(vma, start, foll_flags, &ctx);
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
if (!page || PTR_ERR(page) == -EMLINK) {
ret = faultin_page(vma, start, &foll_flags,
PTR_ERR(page) == -EMLINK, locked);
switch (ret) {
case 0:
goto retry;
case -EBUSY:
mm: avoid unnecessary page fault retires on shared memory types I observed that for each of the shared file-backed page faults, we're very likely to retry one more time for the 1st write fault upon no page. It's because we'll need to release the mmap lock for dirty rate limit purpose with balance_dirty_pages_ratelimited() (in fault_dirty_shared_page()). Then after that throttling we return VM_FAULT_RETRY. We did that probably because VM_FAULT_RETRY is the only way we can return to the fault handler at that time telling it we've released the mmap lock. However that's not ideal because it's very likely the fault does not need to be retried at all since the pgtable was well installed before the throttling, so the next continuous fault (including taking mmap read lock, walk the pgtable, etc.) could be in most cases unnecessary. It's not only slowing down page faults for shared file-backed, but also add more mmap lock contention which is in most cases not needed at all. To observe this, one could try to write to some shmem page and look at "pgfault" value in /proc/vmstat, then we should expect 2 counts for each shmem write simply because we retried, and vm event "pgfault" will capture that. To make it more efficient, add a new VM_FAULT_COMPLETED return code just to show that we've completed the whole fault and released the lock. It's also a hint that we should very possibly not need another fault immediately on this page because we've just completed it. This patch provides a ~12% perf boost on my aarch64 test VM with a simple program sequentially dirtying 400MB shmem file being mmap()ed and these are the time it needs: Before: 650.980 ms (+-1.94%) After: 569.396 ms (+-1.38%) I believe it could help more than that. We need some special care on GUP and the s390 pgfault handler (for gmap code before returning from pgfault), the rest changes in the page fault handlers should be relatively straightforward. Another thing to mention is that mm_account_fault() does take this new fault as a generic fault to be accounted, unlike VM_FAULT_RETRY. I explicitly didn't touch hmm_vma_fault() and break_ksm() because they do not handle VM_FAULT_RETRY even with existing code, so I'm literally keeping them as-is. Link: https://lkml.kernel.org/r/20220530183450.42886-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Vineet Gupta <vgupta@kernel.org> Acked-by: Guo Ren <guoren@kernel.org> Acked-by: Max Filippov <jcmvbkbc@gmail.com> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) Acked-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Alistair Popple <apopple@nvidia.com> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> [arm part] Acked-by: Heiko Carstens <hca@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Stafford Horne <shorne@gmail.com> Cc: David S. Miller <davem@davemloft.net> Cc: Johannes Berg <johannes@sipsolutions.net> Cc: Brian Cain <bcain@quicinc.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Richard Weinberger <richard@nod.at> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Janosch Frank <frankja@linux.ibm.com> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Jonas Bonn <jonas@southpole.se> Cc: Will Deacon <will@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Michal Simek <monstr@monstr.eu> Cc: Matt Turner <mattst88@gmail.com> Cc: Paul Mackerras <paulus@samba.org> Cc: David Hildenbrand <david@redhat.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Chris Zankel <chris@zankel.net> Cc: Hugh Dickins <hughd@google.com> Cc: Dinh Nguyen <dinguyen@kernel.org> Cc: Rich Felker <dalias@libc.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Helge Deller <deller@gmx.de> Cc: Yoshinori Sato <ysato@users.osdn.me> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-31 02:34:50 +08:00
case -EAGAIN:
ret = 0;
fallthrough;
case -EFAULT:
case -ENOMEM:
case -EHWPOISON:
goto out;
}
BUG();
} else if (PTR_ERR(page) == -EEXIST) {
/*
* Proper page table entry exists, but no corresponding
* struct page. If the caller expects **pages to be
* filled in, bail out now, because that can't be done
* for this page.
*/
if (pages) {
ret = PTR_ERR(page);
goto out;
}
goto next_page;
} else if (IS_ERR(page)) {
ret = PTR_ERR(page);
goto out;
}
if (pages) {
pages[i] = page;
flush_anon_page(vma, page, start);
flush_dcache_page(page);
ctx.page_mask = 0;
}
next_page:
if (vmas) {
vmas[i] = vma;
ctx.page_mask = 0;
}
page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
if (page_increm > nr_pages)
page_increm = nr_pages;
i += page_increm;
start += page_increm * PAGE_SIZE;
nr_pages -= page_increm;
} while (nr_pages);
out:
if (ctx.pgmap)
put_dev_pagemap(ctx.pgmap);
return i ? i : ret;
}
static bool vma_permits_fault(struct vm_area_struct *vma,
unsigned int fault_flags)
{
mm/core: Do not enforce PKEY permissions on remote mm access We try to enforce protection keys in software the same way that we do in hardware. (See long example below). But, we only want to do this when accessing our *own* process's memory. If GDB set PKRU[6].AD=1 (disable access to PKEY 6), then tried to PTRACE_POKE a target process which just happened to have some mprotect_pkey(pkey=6) memory, we do *not* want to deny the debugger access to that memory. PKRU is fundamentally a thread-local structure and we do not want to enforce it on access to _another_ thread's data. This gets especially tricky when we have workqueues or other delayed-work mechanisms that might run in a random process's context. We can check that we only enforce pkeys when operating on our *own* mm, but delayed work gets performed when a random user context is active. We might end up with a situation where a delayed-work gup fails when running randomly under its "own" task but succeeds when running under another process. We want to avoid that. To avoid that, we use the new GUP flag: FOLL_REMOTE and add a fault flag: FAULT_FLAG_REMOTE. They indicate that we are walking an mm which is not guranteed to be the same as current->mm and should not be subject to protection key enforcement. Thanks to Jerome Glisse for pointing out this scenario. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <dchinner@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Geliang Tang <geliangtang@163.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Xie XiuQi <xiexiuqi@huawei.com> Cc: iommu@lists.linux-foundation.org Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:21 +08:00
bool write = !!(fault_flags & FAULT_FLAG_WRITE);
bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys Today, for normal faults and page table walks, we check the VMA and/or PTE to ensure that it is compatible with the action. For instance, if we get a write fault on a non-writeable VMA, we SIGSEGV. We try to do the same thing for protection keys. Basically, we try to make sure that if a user does this: mprotect(ptr, size, PROT_NONE); *ptr = foo; they see the same effects with protection keys when they do this: mprotect(ptr, size, PROT_READ|PROT_WRITE); set_pkey(ptr, size, 4); wrpkru(0xffffff3f); // access disable pkey 4 *ptr = foo; The state to do that checking is in the VMA, but we also sometimes have to do it on the page tables only, like when doing a get_user_pages_fast() where we have no VMA. We add two functions and expose them to generic code: arch_pte_access_permitted(pte_flags, write) arch_vma_access_permitted(vma, write) These are, of course, backed up in x86 arch code with checks against the PTE or VMA's protection key. But, there are also cases where we do not want to respect protection keys. When we ptrace(), for instance, we do not want to apply the tracer's PKRU permissions to the PTEs from the process being traced. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave@sr71.net> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: David Hildenbrand <dahi@linux.vnet.ibm.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20160212210219.14D5D715@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:19 +08:00
vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
if (!(vm_flags & vma->vm_flags))
return false;
mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys Today, for normal faults and page table walks, we check the VMA and/or PTE to ensure that it is compatible with the action. For instance, if we get a write fault on a non-writeable VMA, we SIGSEGV. We try to do the same thing for protection keys. Basically, we try to make sure that if a user does this: mprotect(ptr, size, PROT_NONE); *ptr = foo; they see the same effects with protection keys when they do this: mprotect(ptr, size, PROT_READ|PROT_WRITE); set_pkey(ptr, size, 4); wrpkru(0xffffff3f); // access disable pkey 4 *ptr = foo; The state to do that checking is in the VMA, but we also sometimes have to do it on the page tables only, like when doing a get_user_pages_fast() where we have no VMA. We add two functions and expose them to generic code: arch_pte_access_permitted(pte_flags, write) arch_vma_access_permitted(vma, write) These are, of course, backed up in x86 arch code with checks against the PTE or VMA's protection key. But, there are also cases where we do not want to respect protection keys. When we ptrace(), for instance, we do not want to apply the tracer's PKRU permissions to the PTEs from the process being traced. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave@sr71.net> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: David Hildenbrand <dahi@linux.vnet.ibm.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20160212210219.14D5D715@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:19 +08:00
/*
* The architecture might have a hardware protection
mm/core: Do not enforce PKEY permissions on remote mm access We try to enforce protection keys in software the same way that we do in hardware. (See long example below). But, we only want to do this when accessing our *own* process's memory. If GDB set PKRU[6].AD=1 (disable access to PKEY 6), then tried to PTRACE_POKE a target process which just happened to have some mprotect_pkey(pkey=6) memory, we do *not* want to deny the debugger access to that memory. PKRU is fundamentally a thread-local structure and we do not want to enforce it on access to _another_ thread's data. This gets especially tricky when we have workqueues or other delayed-work mechanisms that might run in a random process's context. We can check that we only enforce pkeys when operating on our *own* mm, but delayed work gets performed when a random user context is active. We might end up with a situation where a delayed-work gup fails when running randomly under its "own" task but succeeds when running under another process. We want to avoid that. To avoid that, we use the new GUP flag: FOLL_REMOTE and add a fault flag: FAULT_FLAG_REMOTE. They indicate that we are walking an mm which is not guranteed to be the same as current->mm and should not be subject to protection key enforcement. Thanks to Jerome Glisse for pointing out this scenario. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <dchinner@redhat.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Geliang Tang <geliangtang@163.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Xie XiuQi <xiexiuqi@huawei.com> Cc: iommu@lists.linux-foundation.org Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:21 +08:00
* mechanism other than read/write that can deny access.
mm/core, x86/mm/pkeys: Differentiate instruction fetches As discussed earlier, we attempt to enforce protection keys in software. However, the code checks all faults to ensure that they are not violating protection key permissions. It was assumed that all faults are either write faults where we check PKRU[key].WD (write disable) or read faults where we check the AD (access disable) bit. But, there is a third category of faults for protection keys: instruction faults. Instruction faults never run afoul of protection keys because they do not affect instruction fetches. So, plumb the PF_INSTR bit down in to the arch_vma_access_permitted() function where we do the protection key checks. We also add a new FAULT_FLAG_INSTRUCTION. This is because handle_mm_fault() is not passed the architecture-specific error_code where we keep PF_INSTR, so we need to encode the instruction fetch information in to the arch-generic fault flags. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave@sr71.net> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20160212210224.96928009@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:24 +08:00
*
* gup always represents data access, not instruction
* fetches, so execute=false here:
mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys Today, for normal faults and page table walks, we check the VMA and/or PTE to ensure that it is compatible with the action. For instance, if we get a write fault on a non-writeable VMA, we SIGSEGV. We try to do the same thing for protection keys. Basically, we try to make sure that if a user does this: mprotect(ptr, size, PROT_NONE); *ptr = foo; they see the same effects with protection keys when they do this: mprotect(ptr, size, PROT_READ|PROT_WRITE); set_pkey(ptr, size, 4); wrpkru(0xffffff3f); // access disable pkey 4 *ptr = foo; The state to do that checking is in the VMA, but we also sometimes have to do it on the page tables only, like when doing a get_user_pages_fast() where we have no VMA. We add two functions and expose them to generic code: arch_pte_access_permitted(pte_flags, write) arch_vma_access_permitted(vma, write) These are, of course, backed up in x86 arch code with checks against the PTE or VMA's protection key. But, there are also cases where we do not want to respect protection keys. When we ptrace(), for instance, we do not want to apply the tracer's PKRU permissions to the PTEs from the process being traced. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave@sr71.net> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: David Hildenbrand <dahi@linux.vnet.ibm.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20160212210219.14D5D715@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:19 +08:00
*/
mm/core, x86/mm/pkeys: Differentiate instruction fetches As discussed earlier, we attempt to enforce protection keys in software. However, the code checks all faults to ensure that they are not violating protection key permissions. It was assumed that all faults are either write faults where we check PKRU[key].WD (write disable) or read faults where we check the AD (access disable) bit. But, there is a third category of faults for protection keys: instruction faults. Instruction faults never run afoul of protection keys because they do not affect instruction fetches. So, plumb the PF_INSTR bit down in to the arch_vma_access_permitted() function where we do the protection key checks. We also add a new FAULT_FLAG_INSTRUCTION. This is because handle_mm_fault() is not passed the architecture-specific error_code where we keep PF_INSTR, so we need to encode the instruction fetch information in to the arch-generic fault flags. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave@sr71.net> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20160212210224.96928009@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:24 +08:00
if (!arch_vma_access_permitted(vma, write, false, foreign))
mm/gup, x86/mm/pkeys: Check VMAs and PTEs for protection keys Today, for normal faults and page table walks, we check the VMA and/or PTE to ensure that it is compatible with the action. For instance, if we get a write fault on a non-writeable VMA, we SIGSEGV. We try to do the same thing for protection keys. Basically, we try to make sure that if a user does this: mprotect(ptr, size, PROT_NONE); *ptr = foo; they see the same effects with protection keys when they do this: mprotect(ptr, size, PROT_READ|PROT_WRITE); set_pkey(ptr, size, 4); wrpkru(0xffffff3f); // access disable pkey 4 *ptr = foo; The state to do that checking is in the VMA, but we also sometimes have to do it on the page tables only, like when doing a get_user_pages_fast() where we have no VMA. We add two functions and expose them to generic code: arch_pte_access_permitted(pte_flags, write) arch_vma_access_permitted(vma, write) These are, of course, backed up in x86 arch code with checks against the PTE or VMA's protection key. But, there are also cases where we do not want to respect protection keys. When we ptrace(), for instance, we do not want to apply the tracer's PKRU permissions to the PTEs from the process being traced. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Alexey Kardashevskiy <aik@ozlabs.ru> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Boaz Harrosh <boaz@plexistor.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave@sr71.net> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: David Hildenbrand <dahi@linux.vnet.ibm.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Dominik Vogt <vogt@linux.vnet.ibm.com> Cc: Guan Xuetao <gxt@mprc.pku.edu.cn> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Low <jason.low2@hp.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Hocko <mhocko@suse.com> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Shachar Raindel <raindel@mellanox.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: linux-arch@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-s390@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20160212210219.14D5D715@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-02-13 05:02:19 +08:00
return false;
return true;
}
/**
* fixup_user_fault() - manually resolve a user page fault
* @mm: mm_struct of target mm
* @address: user address
* @fault_flags:flags to pass down to handle_mm_fault()
* @unlocked: did we unlock the mmap_lock while retrying, maybe NULL if caller
* does not allow retry. If NULL, the caller must guarantee
* that fault_flags does not contain FAULT_FLAG_ALLOW_RETRY.
*
* This is meant to be called in the specific scenario where for locking reasons
* we try to access user memory in atomic context (within a pagefault_disable()
* section), this returns -EFAULT, and we want to resolve the user fault before
* trying again.
*
* Typically this is meant to be used by the futex code.
*
* The main difference with get_user_pages() is that this function will
* unconditionally call handle_mm_fault() which will in turn perform all the
* necessary SW fixup of the dirty and young bits in the PTE, while
mm: bring in additional flag for fixup_user_fault to signal unlock During Jason's work with postcopy migration support for s390 a problem regarding gmap faults was discovered. The gmap code will call fixup_user_fault which will end up always in handle_mm_fault. Till now we never cared about retries, but as the userfaultfd code kind of relies on it. this needs some fix. This patchset does not take care of the futex code. I will now look closer at this. This patch (of 2): With the introduction of userfaultfd, kvm on s390 needs fixup_user_fault to pass in FAULT_FLAG_ALLOW_RETRY and give feedback if during the faulting we ever unlocked mmap_sem. This patch brings in the logic to handle retries as well as it cleans up the current documentation. fixup_user_fault was not having the same semantics as filemap_fault. It never indicated if a retry happened and so a caller wasn't able to handle that case. So we now changed the behaviour to always retry a locked mmap_sem. Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: "Jason J. Herne" <jjherne@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-16 08:57:04 +08:00
* get_user_pages() only guarantees to update these in the struct page.
*
* This is important for some architectures where those bits also gate the
* access permission to the page because they are maintained in software. On
* such architectures, gup() will not be enough to make a subsequent access
* succeed.
*
* This function will not return with an unlocked mmap_lock. So it has not the
* same semantics wrt the @mm->mmap_lock as does filemap_fault().
*/
int fixup_user_fault(struct mm_struct *mm,
mm: bring in additional flag for fixup_user_fault to signal unlock During Jason's work with postcopy migration support for s390 a problem regarding gmap faults was discovered. The gmap code will call fixup_user_fault which will end up always in handle_mm_fault. Till now we never cared about retries, but as the userfaultfd code kind of relies on it. this needs some fix. This patchset does not take care of the futex code. I will now look closer at this. This patch (of 2): With the introduction of userfaultfd, kvm on s390 needs fixup_user_fault to pass in FAULT_FLAG_ALLOW_RETRY and give feedback if during the faulting we ever unlocked mmap_sem. This patch brings in the logic to handle retries as well as it cleans up the current documentation. fixup_user_fault was not having the same semantics as filemap_fault. It never indicated if a retry happened and so a caller wasn't able to handle that case. So we now changed the behaviour to always retry a locked mmap_sem. Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: "Jason J. Herne" <jjherne@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-16 08:57:04 +08:00
unsigned long address, unsigned int fault_flags,
bool *unlocked)
{
struct vm_area_struct *vma;
vm_fault_t ret;
mm: bring in additional flag for fixup_user_fault to signal unlock During Jason's work with postcopy migration support for s390 a problem regarding gmap faults was discovered. The gmap code will call fixup_user_fault which will end up always in handle_mm_fault. Till now we never cared about retries, but as the userfaultfd code kind of relies on it. this needs some fix. This patchset does not take care of the futex code. I will now look closer at this. This patch (of 2): With the introduction of userfaultfd, kvm on s390 needs fixup_user_fault to pass in FAULT_FLAG_ALLOW_RETRY and give feedback if during the faulting we ever unlocked mmap_sem. This patch brings in the logic to handle retries as well as it cleans up the current documentation. fixup_user_fault was not having the same semantics as filemap_fault. It never indicated if a retry happened and so a caller wasn't able to handle that case. So we now changed the behaviour to always retry a locked mmap_sem. Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: "Jason J. Herne" <jjherne@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-16 08:57:04 +08:00
address = untagged_addr_remote(mm, address);
mm: bring in additional flag for fixup_user_fault to signal unlock During Jason's work with postcopy migration support for s390 a problem regarding gmap faults was discovered. The gmap code will call fixup_user_fault which will end up always in handle_mm_fault. Till now we never cared about retries, but as the userfaultfd code kind of relies on it. this needs some fix. This patchset does not take care of the futex code. I will now look closer at this. This patch (of 2): With the introduction of userfaultfd, kvm on s390 needs fixup_user_fault to pass in FAULT_FLAG_ALLOW_RETRY and give feedback if during the faulting we ever unlocked mmap_sem. This patch brings in the logic to handle retries as well as it cleans up the current documentation. fixup_user_fault was not having the same semantics as filemap_fault. It never indicated if a retry happened and so a caller wasn't able to handle that case. So we now changed the behaviour to always retry a locked mmap_sem. Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: "Jason J. Herne" <jjherne@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-16 08:57:04 +08:00
if (unlocked)
mm/gup: allow to react to fatal signals The existing gup code does not react to the fatal signals in many code paths. For example, in one retry path of gup we're still using down_read() rather than down_read_killable(). Also, when doing page faults we don't pass in FAULT_FLAG_KILLABLE as well, which means that within the faulting process we'll wait in non-killable way as well. These were spotted by Linus during the code review of some other patches. Let's allow the gup code to react to fatal signals to improve the responsiveness of threads when during gup and being killed. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: David Hildenbrand <david@redhat.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Martin Cracauer <cracauer@cons.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Matthew Wilcox <willy@infradead.org> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220160256.9887-1-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:08:53 +08:00
fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
mm: bring in additional flag for fixup_user_fault to signal unlock During Jason's work with postcopy migration support for s390 a problem regarding gmap faults was discovered. The gmap code will call fixup_user_fault which will end up always in handle_mm_fault. Till now we never cared about retries, but as the userfaultfd code kind of relies on it. this needs some fix. This patchset does not take care of the futex code. I will now look closer at this. This patch (of 2): With the introduction of userfaultfd, kvm on s390 needs fixup_user_fault to pass in FAULT_FLAG_ALLOW_RETRY and give feedback if during the faulting we ever unlocked mmap_sem. This patch brings in the logic to handle retries as well as it cleans up the current documentation. fixup_user_fault was not having the same semantics as filemap_fault. It never indicated if a retry happened and so a caller wasn't able to handle that case. So we now changed the behaviour to always retry a locked mmap_sem. Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: "Jason J. Herne" <jjherne@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-16 08:57:04 +08:00
retry:
vma = find_extend_vma(mm, address);
if (!vma || address < vma->vm_start)
return -EFAULT;
if (!vma_permits_fault(vma, fault_flags))
return -EFAULT;
if ((fault_flags & FAULT_FLAG_KILLABLE) &&
fatal_signal_pending(current))
return -EINTR;
mm: do page fault accounting in handle_mm_fault Patch series "mm: Page fault accounting cleanups", v5. This is v5 of the pf accounting cleanup series. It originates from Gerald Schaefer's report on an issue a week ago regarding to incorrect page fault accountings for retried page fault after commit 4064b9827063 ("mm: allow VM_FAULT_RETRY for multiple times"): https://lore.kernel.org/lkml/20200610174811.44b94525@thinkpad/ What this series did: - Correct page fault accounting: we do accounting for a page fault (no matter whether it's from #PF handling, or gup, or anything else) only with the one that completed the fault. For example, page fault retries should not be counted in page fault counters. Same to the perf events. - Unify definition of PERF_COUNT_SW_PAGE_FAULTS: currently this perf event is used in an adhoc way across different archs. Case (1): for many archs it's done at the entry of a page fault handler, so that it will also cover e.g. errornous faults. Case (2): for some other archs, it is only accounted when the page fault is resolved successfully. Case (3): there're still quite some archs that have not enabled this perf event. Since this series will touch merely all the archs, we unify this perf event to always follow case (1), which is the one that makes most sense. And since we moved the accounting into handle_mm_fault, the other two MAJ/MIN perf events are well taken care of naturally. - Unify definition of "major faults": the definition of "major fault" is slightly changed when used in accounting (not VM_FAULT_MAJOR). More information in patch 1. - Always account the page fault onto the one that triggered the page fault. This does not matter much for #PF handlings, but mostly for gup. More information on this in patch 25. Patchset layout: Patch 1: Introduced the accounting in handle_mm_fault(), not enabled. Patch 2-23: Enable the new accounting for arch #PF handlers one by one. Patch 24: Enable the new accounting for the rest outliers (gup, iommu, etc.) Patch 25: Cleanup GUP task_struct pointer since it's not needed any more This patch (of 25): This is a preparation patch to move page fault accountings into the general code in handle_mm_fault(). This includes both the per task flt_maj/flt_min counters, and the major/minor page fault perf events. To do this, the pt_regs pointer is passed into handle_mm_fault(). PERF_COUNT_SW_PAGE_FAULTS should still be kept in per-arch page fault handlers. So far, all the pt_regs pointer that passed into handle_mm_fault() is NULL, which means this patch should have no intented functional change. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Cain <bcain@codeaurora.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Chris Zankel <chris@zankel.net> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David S. Miller <davem@davemloft.net> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com> Cc: Greentime Hu <green.hu@gmail.com> Cc: Guo Ren <guoren@kernel.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Helge Deller <deller@gmx.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jonas Bonn <jonas@southpole.se> Cc: Ley Foon Tan <ley.foon.tan@intel.com> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Matt Turner <mattst88@gmail.com> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Michal Simek <monstr@monstr.eu> Cc: Nick Hu <nickhu@andestech.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Richard Henderson <rth@twiddle.net> Cc: Rich Felker <dalias@libc.org> Cc: Russell King <linux@armlinux.org.uk> Cc: Stafford Horne <shorne@gmail.com> Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Vincent Chen <deanbo422@gmail.com> Cc: Vineet Gupta <vgupta@synopsys.com> Cc: Will Deacon <will@kernel.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Link: http://lkml.kernel.org/r/20200707225021.200906-1-peterx@redhat.com Link: http://lkml.kernel.org/r/20200707225021.200906-2-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-08-12 09:37:44 +08:00
ret = handle_mm_fault(vma, address, fault_flags, NULL);
mm: avoid unnecessary page fault retires on shared memory types I observed that for each of the shared file-backed page faults, we're very likely to retry one more time for the 1st write fault upon no page. It's because we'll need to release the mmap lock for dirty rate limit purpose with balance_dirty_pages_ratelimited() (in fault_dirty_shared_page()). Then after that throttling we return VM_FAULT_RETRY. We did that probably because VM_FAULT_RETRY is the only way we can return to the fault handler at that time telling it we've released the mmap lock. However that's not ideal because it's very likely the fault does not need to be retried at all since the pgtable was well installed before the throttling, so the next continuous fault (including taking mmap read lock, walk the pgtable, etc.) could be in most cases unnecessary. It's not only slowing down page faults for shared file-backed, but also add more mmap lock contention which is in most cases not needed at all. To observe this, one could try to write to some shmem page and look at "pgfault" value in /proc/vmstat, then we should expect 2 counts for each shmem write simply because we retried, and vm event "pgfault" will capture that. To make it more efficient, add a new VM_FAULT_COMPLETED return code just to show that we've completed the whole fault and released the lock. It's also a hint that we should very possibly not need another fault immediately on this page because we've just completed it. This patch provides a ~12% perf boost on my aarch64 test VM with a simple program sequentially dirtying 400MB shmem file being mmap()ed and these are the time it needs: Before: 650.980 ms (+-1.94%) After: 569.396 ms (+-1.38%) I believe it could help more than that. We need some special care on GUP and the s390 pgfault handler (for gmap code before returning from pgfault), the rest changes in the page fault handlers should be relatively straightforward. Another thing to mention is that mm_account_fault() does take this new fault as a generic fault to be accounted, unlike VM_FAULT_RETRY. I explicitly didn't touch hmm_vma_fault() and break_ksm() because they do not handle VM_FAULT_RETRY even with existing code, so I'm literally keeping them as-is. Link: https://lkml.kernel.org/r/20220530183450.42886-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Vineet Gupta <vgupta@kernel.org> Acked-by: Guo Ren <guoren@kernel.org> Acked-by: Max Filippov <jcmvbkbc@gmail.com> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) Acked-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Alistair Popple <apopple@nvidia.com> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> [arm part] Acked-by: Heiko Carstens <hca@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Stafford Horne <shorne@gmail.com> Cc: David S. Miller <davem@davemloft.net> Cc: Johannes Berg <johannes@sipsolutions.net> Cc: Brian Cain <bcain@quicinc.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Richard Weinberger <richard@nod.at> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Janosch Frank <frankja@linux.ibm.com> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Jonas Bonn <jonas@southpole.se> Cc: Will Deacon <will@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Michal Simek <monstr@monstr.eu> Cc: Matt Turner <mattst88@gmail.com> Cc: Paul Mackerras <paulus@samba.org> Cc: David Hildenbrand <david@redhat.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Chris Zankel <chris@zankel.net> Cc: Hugh Dickins <hughd@google.com> Cc: Dinh Nguyen <dinguyen@kernel.org> Cc: Rich Felker <dalias@libc.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Helge Deller <deller@gmx.de> Cc: Yoshinori Sato <ysato@users.osdn.me> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-31 02:34:50 +08:00
if (ret & VM_FAULT_COMPLETED) {
/*
* NOTE: it's a pity that we need to retake the lock here
* to pair with the unlock() in the callers. Ideally we
* could tell the callers so they do not need to unlock.
*/
mmap_read_lock(mm);
*unlocked = true;
return 0;
}
if (ret & VM_FAULT_ERROR) {
mm/hugetlb: report -EHWPOISON not -EFAULT when FOLL_HWPOISON is specified KVM uses get_user_pages() to resolve its stage2 faults. KVM sets the FOLL_HWPOISON flag causing faultin_page() to return -EHWPOISON when it finds a VM_FAULT_HWPOISON. KVM handles these hwpoison pages as a special case. (check_user_page_hwpoison()) When huge pages are involved, this doesn't work so well. get_user_pages() calls follow_hugetlb_page(), which stops early if it receives VM_FAULT_HWPOISON from hugetlb_fault(), eventually returning -EFAULT to the caller. The step to map this to -EHWPOISON based on the FOLL_ flags is missing. The hwpoison special case is skipped, and -EFAULT is returned to user-space, causing Qemu or kvmtool to exit. Instead, move this VM_FAULT_ to errno mapping code into a header file and use it from faultin_page() and follow_hugetlb_page(). With this, KVM works as expected. This isn't a problem for arm64 today as we haven't enabled MEMORY_FAILURE, but I can't see any reason this doesn't happen on x86 too, so I think this should be a fix. This doesn't apply earlier than stable's v4.11.1 due to all sorts of cleanup. [james.morse@arm.com: add vm_fault_to_errno() call to faultin_page()] suggested. Link: http://lkml.kernel.org/r/20170525171035.16359-1-james.morse@arm.com [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20170524160900.28786-1-james.morse@arm.com Signed-off-by: James Morse <james.morse@arm.com> Acked-by: Punit Agrawal <punit.agrawal@arm.com> Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com> Cc: <stable@vger.kernel.org> [4.11.1+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-06-03 05:46:46 +08:00
int err = vm_fault_to_errno(ret, 0);
if (err)
return err;
BUG();
}
mm: bring in additional flag for fixup_user_fault to signal unlock During Jason's work with postcopy migration support for s390 a problem regarding gmap faults was discovered. The gmap code will call fixup_user_fault which will end up always in handle_mm_fault. Till now we never cared about retries, but as the userfaultfd code kind of relies on it. this needs some fix. This patchset does not take care of the futex code. I will now look closer at this. This patch (of 2): With the introduction of userfaultfd, kvm on s390 needs fixup_user_fault to pass in FAULT_FLAG_ALLOW_RETRY and give feedback if during the faulting we ever unlocked mmap_sem. This patch brings in the logic to handle retries as well as it cleans up the current documentation. fixup_user_fault was not having the same semantics as filemap_fault. It never indicated if a retry happened and so a caller wasn't able to handle that case. So we now changed the behaviour to always retry a locked mmap_sem. Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: "Jason J. Herne" <jjherne@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-16 08:57:04 +08:00
if (ret & VM_FAULT_RETRY) {
mmap locking API: use coccinelle to convert mmap_sem rwsem call sites This change converts the existing mmap_sem rwsem calls to use the new mmap locking API instead. The change is generated using coccinelle with the following rule: // spatch --sp-file mmap_lock_api.cocci --in-place --include-headers --dir . @@ expression mm; @@ ( -init_rwsem +mmap_init_lock | -down_write +mmap_write_lock | -down_write_killable +mmap_write_lock_killable | -down_write_trylock +mmap_write_trylock | -up_write +mmap_write_unlock | -downgrade_write +mmap_write_downgrade | -down_read +mmap_read_lock | -down_read_killable +mmap_read_lock_killable | -down_read_trylock +mmap_read_trylock | -up_read +mmap_read_unlock ) -(&mm->mmap_sem) +(mm) Signed-off-by: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jerome Glisse <jglisse@redhat.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Liam Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ying Han <yinghan@google.com> Link: http://lkml.kernel.org/r/20200520052908.204642-5-walken@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-09 12:33:25 +08:00
mmap_read_lock(mm);
*unlocked = true;
fault_flags |= FAULT_FLAG_TRIED;
goto retry;
mm: bring in additional flag for fixup_user_fault to signal unlock During Jason's work with postcopy migration support for s390 a problem regarding gmap faults was discovered. The gmap code will call fixup_user_fault which will end up always in handle_mm_fault. Till now we never cared about retries, but as the userfaultfd code kind of relies on it. this needs some fix. This patchset does not take care of the futex code. I will now look closer at this. This patch (of 2): With the introduction of userfaultfd, kvm on s390 needs fixup_user_fault to pass in FAULT_FLAG_ALLOW_RETRY and give feedback if during the faulting we ever unlocked mmap_sem. This patch brings in the logic to handle retries as well as it cleans up the current documentation. fixup_user_fault was not having the same semantics as filemap_fault. It never indicated if a retry happened and so a caller wasn't able to handle that case. So we now changed the behaviour to always retry a locked mmap_sem. Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: "Jason J. Herne" <jjherne@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Eric B Munson <emunson@akamai.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Dominik Dingel <dingel@linux.vnet.ibm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-16 08:57:04 +08:00
}
return 0;
}
EXPORT_SYMBOL_GPL(fixup_user_fault);
mm/gup: Add FOLL_INTERRUPTIBLE We have had FAULT_FLAG_INTERRUPTIBLE but it was never applied to GUPs. One issue with it is that not all GUP paths are able to handle signal delivers besides SIGKILL. That's not ideal for the GUP users who are actually able to handle these cases, like KVM. KVM uses GUP extensively on faulting guest pages, during which we've got existing infrastructures to retry a page fault at a later time. Allowing the GUP to be interrupted by generic signals can make KVM related threads to be more responsive. For examples: (1) SIGUSR1: which QEMU/KVM uses to deliver an inter-process IPI, e.g. when the admin issues a vm_stop QMP command, SIGUSR1 can be generated to kick the vcpus out of kernel context immediately, (2) SIGINT: which can be used with interactive hypervisor users to stop a virtual machine with Ctrl-C without any delays/hangs, (3) SIGTRAP: which grants GDB capability even during page faults that are stuck for a long time. Normally hypervisor will be able to receive these signals properly, but not if we're stuck in a GUP for a long time for whatever reason. It happens easily with a stucked postcopy migration when e.g. a network temp failure happens, then some vcpu threads can hang death waiting for the pages. With the new FOLL_INTERRUPTIBLE, we can allow GUP users like KVM to selectively enable the ability to trap these signals. Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20221011195809.557016-2-peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2022-10-12 03:58:06 +08:00
/*
* GUP always responds to fatal signals. When FOLL_INTERRUPTIBLE is
* specified, it'll also respond to generic signals. The caller of GUP
* that has FOLL_INTERRUPTIBLE should take care of the GUP interruption.
*/
static bool gup_signal_pending(unsigned int flags)
{
if (fatal_signal_pending(current))
return true;
if (!(flags & FOLL_INTERRUPTIBLE))
return false;
return signal_pending(current);
}
/*
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
* Locking: (*locked == 1) means that the mmap_lock has already been acquired by
* the caller. This function may drop the mmap_lock. If it does so, then it will
* set (*locked = 0).
*
* (*locked == 0) means that the caller expects this function to acquire and
* drop the mmap_lock. Therefore, the value of *locked will still be zero when
* the function returns, even though it may have changed temporarily during
* function execution.
*
* Please note that this function, unlike __get_user_pages(), will not return 0
* for nr_pages > 0, unless FOLL_NOWAIT is used.
*/
static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
unsigned long start,
unsigned long nr_pages,
struct page **pages,
struct vm_area_struct **vmas,
int *locked,
unsigned int flags)
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
{
long ret, pages_done;
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
bool must_unlock = false;
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
/*
* The internal caller expects GUP to manage the lock internally and the
* lock must be released when this returns.
*/
if (!*locked) {
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
if (mmap_read_lock_killable(mm))
return -EAGAIN;
must_unlock = true;
*locked = 1;
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
}
else
mmap_assert_locked(mm);
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
mm: gup: pack has_pinned in MMF_HAS_PINNED has_pinned 32bit can be packed in the MMF_HAS_PINNED bit as a noop cleanup. Any atomic_inc/dec to the mm cacheline shared by all threads in pin-fast would reintroduce a loss of SMP scalability to pin-fast, so there's no future potential usefulness to keep an atomic in the mm for this. set_bit(MMF_HAS_PINNED) will be theoretically a bit slower than WRITE_ONCE (atomic_set is equivalent to WRITE_ONCE), but the set_bit (just like atomic_set after this commit) has to be still issued only once per "mm", so the difference between the two will be lost in the noise. will-it-scale "mmap2" shows no change in performance with enterprise config as expected. will-it-scale "pin_fast" retains the > 4000% SMP scalability performance improvement against upstream as expected. This is a noop as far as overall performance and SMP scalability are concerned. [peterx@redhat.com: pack has_pinned in MMF_HAS_PINNED] Link: https://lkml.kernel.org/r/YJqWESqyxa8OZA+2@t490s [akpm@linux-foundation.org: coding style fixes] [peterx@redhat.com: fix build for task_mmu.c, introduce mm_set_has_pinned_flag, fix comments] Link: https://lkml.kernel.org/r/20210507150553.208763-4-peterx@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Kirill Shutemov <kirill@shutemov.name> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:36:40 +08:00
if (flags & FOLL_PIN)
mm_set_has_pinned_flag(&mm->flags);
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
/*
* FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior
* is to set FOLL_GET if the caller wants pages[] filled in (but has
* carelessly failed to specify FOLL_GET), so keep doing that, but only
* for FOLL_GET, not for the newer FOLL_PIN.
*
* FOLL_PIN always expects pages to be non-null, but no need to assert
* that here, as any failures will be obvious enough.
*/
if (pages && !(flags & FOLL_PIN))
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
flags |= FOLL_GET;
pages_done = 0;
for (;;) {
ret = __get_user_pages(mm, start, nr_pages, flags, pages,
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
vmas, locked);
if (!(flags & FOLL_UNLOCKABLE)) {
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
/* VM_FAULT_RETRY couldn't trigger, bypass */
pages_done = ret;
break;
}
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
mm: avoid unnecessary page fault retires on shared memory types I observed that for each of the shared file-backed page faults, we're very likely to retry one more time for the 1st write fault upon no page. It's because we'll need to release the mmap lock for dirty rate limit purpose with balance_dirty_pages_ratelimited() (in fault_dirty_shared_page()). Then after that throttling we return VM_FAULT_RETRY. We did that probably because VM_FAULT_RETRY is the only way we can return to the fault handler at that time telling it we've released the mmap lock. However that's not ideal because it's very likely the fault does not need to be retried at all since the pgtable was well installed before the throttling, so the next continuous fault (including taking mmap read lock, walk the pgtable, etc.) could be in most cases unnecessary. It's not only slowing down page faults for shared file-backed, but also add more mmap lock contention which is in most cases not needed at all. To observe this, one could try to write to some shmem page and look at "pgfault" value in /proc/vmstat, then we should expect 2 counts for each shmem write simply because we retried, and vm event "pgfault" will capture that. To make it more efficient, add a new VM_FAULT_COMPLETED return code just to show that we've completed the whole fault and released the lock. It's also a hint that we should very possibly not need another fault immediately on this page because we've just completed it. This patch provides a ~12% perf boost on my aarch64 test VM with a simple program sequentially dirtying 400MB shmem file being mmap()ed and these are the time it needs: Before: 650.980 ms (+-1.94%) After: 569.396 ms (+-1.38%) I believe it could help more than that. We need some special care on GUP and the s390 pgfault handler (for gmap code before returning from pgfault), the rest changes in the page fault handlers should be relatively straightforward. Another thing to mention is that mm_account_fault() does take this new fault as a generic fault to be accounted, unlike VM_FAULT_RETRY. I explicitly didn't touch hmm_vma_fault() and break_ksm() because they do not handle VM_FAULT_RETRY even with existing code, so I'm literally keeping them as-is. Link: https://lkml.kernel.org/r/20220530183450.42886-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Vineet Gupta <vgupta@kernel.org> Acked-by: Guo Ren <guoren@kernel.org> Acked-by: Max Filippov <jcmvbkbc@gmail.com> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) Acked-by: Catalin Marinas <catalin.marinas@arm.com> Reviewed-by: Alistair Popple <apopple@nvidia.com> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk> [arm part] Acked-by: Heiko Carstens <hca@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Stafford Horne <shorne@gmail.com> Cc: David S. Miller <davem@davemloft.net> Cc: Johannes Berg <johannes@sipsolutions.net> Cc: Brian Cain <bcain@quicinc.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Richard Weinberger <richard@nod.at> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Janosch Frank <frankja@linux.ibm.com> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Jonas Bonn <jonas@southpole.se> Cc: Will Deacon <will@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Michal Simek <monstr@monstr.eu> Cc: Matt Turner <mattst88@gmail.com> Cc: Paul Mackerras <paulus@samba.org> Cc: David Hildenbrand <david@redhat.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Chris Zankel <chris@zankel.net> Cc: Hugh Dickins <hughd@google.com> Cc: Dinh Nguyen <dinguyen@kernel.org> Cc: Rich Felker <dalias@libc.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Helge Deller <deller@gmx.de> Cc: Yoshinori Sato <ysato@users.osdn.me> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-31 02:34:50 +08:00
/* VM_FAULT_RETRY or VM_FAULT_COMPLETED cannot return errors */
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
if (!*locked) {
BUG_ON(ret < 0);
BUG_ON(ret >= nr_pages);
}
if (ret > 0) {
nr_pages -= ret;
pages_done += ret;
if (!nr_pages)
break;
}
if (*locked) {
/*
* VM_FAULT_RETRY didn't trigger or it was a
* FOLL_NOWAIT.
*/
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
if (!pages_done)
pages_done = ret;
break;
}
mm/gup: continue VM_FAULT_RETRY processing even for pre-faults When get_user_pages*() is called with pages = NULL, the processing of VM_FAULT_RETRY terminates early without actually retrying to fault-in all the pages. If the pages in the requested range belong to a VMA that has userfaultfd registered, handle_userfault() returns VM_FAULT_RETRY *after* user space has populated the page, but for the gup pre-fault case there's no actual retry and the caller will get no pages although they are present. This issue was uncovered when running post-copy memory restore in CRIU after d9c9ce34ed5c ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails"). After this change, the copying of FPU state to the sigframe switched from copy_to_user() variants which caused a real page fault to get_user_pages() with pages parameter set to NULL. In post-copy mode of CRIU, the destination memory is managed with userfaultfd and lack of the retry for pre-fault case in get_user_pages() causes a crash of the restored process. Making the pre-fault behavior of get_user_pages() the same as the "normal" one fixes the issue. Link: http://lkml.kernel.org/r/1557844195-18882-1-git-send-email-rppt@linux.ibm.com Fixes: d9c9ce34ed5c ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails") Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Tested-by: Andrei Vagin <avagin@gmail.com> [https://travis-ci.org/avagin/linux/builds/533184940] Tested-by: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Borislav Petkov <bp@suse.de> Cc: Pavel Machek <pavel@ucw.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-06-01 13:30:33 +08:00
/*
* VM_FAULT_RETRY triggered, so seek to the faulting offset.
* For the prefault case (!pages) we only update counts.
*/
if (likely(pages))
pages += ret;
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
start += ret << PAGE_SHIFT;
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
/* The lock was temporarily dropped, so we must unlock later */
must_unlock = true;
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
retry:
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
/*
* Repeat on the address that fired VM_FAULT_RETRY
* with both FAULT_FLAG_ALLOW_RETRY and
* FAULT_FLAG_TRIED. Note that GUP can be interrupted
mm/gup: Add FOLL_INTERRUPTIBLE We have had FAULT_FLAG_INTERRUPTIBLE but it was never applied to GUPs. One issue with it is that not all GUP paths are able to handle signal delivers besides SIGKILL. That's not ideal for the GUP users who are actually able to handle these cases, like KVM. KVM uses GUP extensively on faulting guest pages, during which we've got existing infrastructures to retry a page fault at a later time. Allowing the GUP to be interrupted by generic signals can make KVM related threads to be more responsive. For examples: (1) SIGUSR1: which QEMU/KVM uses to deliver an inter-process IPI, e.g. when the admin issues a vm_stop QMP command, SIGUSR1 can be generated to kick the vcpus out of kernel context immediately, (2) SIGINT: which can be used with interactive hypervisor users to stop a virtual machine with Ctrl-C without any delays/hangs, (3) SIGTRAP: which grants GDB capability even during page faults that are stuck for a long time. Normally hypervisor will be able to receive these signals properly, but not if we're stuck in a GUP for a long time for whatever reason. It happens easily with a stucked postcopy migration when e.g. a network temp failure happens, then some vcpu threads can hang death waiting for the pages. With the new FOLL_INTERRUPTIBLE, we can allow GUP users like KVM to selectively enable the ability to trap these signals. Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20221011195809.557016-2-peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2022-10-12 03:58:06 +08:00
* by fatal signals of even common signals, depending on
* the caller's request. So we need to check it before we
* start trying again otherwise it can loop forever.
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
*/
mm/gup: Add FOLL_INTERRUPTIBLE We have had FAULT_FLAG_INTERRUPTIBLE but it was never applied to GUPs. One issue with it is that not all GUP paths are able to handle signal delivers besides SIGKILL. That's not ideal for the GUP users who are actually able to handle these cases, like KVM. KVM uses GUP extensively on faulting guest pages, during which we've got existing infrastructures to retry a page fault at a later time. Allowing the GUP to be interrupted by generic signals can make KVM related threads to be more responsive. For examples: (1) SIGUSR1: which QEMU/KVM uses to deliver an inter-process IPI, e.g. when the admin issues a vm_stop QMP command, SIGUSR1 can be generated to kick the vcpus out of kernel context immediately, (2) SIGINT: which can be used with interactive hypervisor users to stop a virtual machine with Ctrl-C without any delays/hangs, (3) SIGTRAP: which grants GDB capability even during page faults that are stuck for a long time. Normally hypervisor will be able to receive these signals properly, but not if we're stuck in a GUP for a long time for whatever reason. It happens easily with a stucked postcopy migration when e.g. a network temp failure happens, then some vcpu threads can hang death waiting for the pages. With the new FOLL_INTERRUPTIBLE, we can allow GUP users like KVM to selectively enable the ability to trap these signals. Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20221011195809.557016-2-peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2022-10-12 03:58:06 +08:00
if (gup_signal_pending(flags)) {
if (!pages_done)
pages_done = -EINTR;
break;
}
mmap locking API: use coccinelle to convert mmap_sem rwsem call sites This change converts the existing mmap_sem rwsem calls to use the new mmap locking API instead. The change is generated using coccinelle with the following rule: // spatch --sp-file mmap_lock_api.cocci --in-place --include-headers --dir . @@ expression mm; @@ ( -init_rwsem +mmap_init_lock | -down_write +mmap_write_lock | -down_write_killable +mmap_write_lock_killable | -down_write_trylock +mmap_write_trylock | -up_write +mmap_write_unlock | -downgrade_write +mmap_write_downgrade | -down_read +mmap_read_lock | -down_read_killable +mmap_read_lock_killable | -down_read_trylock +mmap_read_trylock | -up_read +mmap_read_unlock ) -(&mm->mmap_sem) +(mm) Signed-off-by: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jerome Glisse <jglisse@redhat.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Liam Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ying Han <yinghan@google.com> Link: http://lkml.kernel.org/r/20200520052908.204642-5-walken@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-09 12:33:25 +08:00
ret = mmap_read_lock_killable(mm);
mm/gup: allow to react to fatal signals The existing gup code does not react to the fatal signals in many code paths. For example, in one retry path of gup we're still using down_read() rather than down_read_killable(). Also, when doing page faults we don't pass in FAULT_FLAG_KILLABLE as well, which means that within the faulting process we'll wait in non-killable way as well. These were spotted by Linus during the code review of some other patches. Let's allow the gup code to react to fatal signals to improve the responsiveness of threads when during gup and being killed. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: David Hildenbrand <david@redhat.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Martin Cracauer <cracauer@cons.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Matthew Wilcox <willy@infradead.org> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220160256.9887-1-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:08:53 +08:00
if (ret) {
BUG_ON(ret > 0);
if (!pages_done)
pages_done = ret;
break;
}
*locked = 1;
ret = __get_user_pages(mm, start, 1, flags | FOLL_TRIED,
pages, NULL, locked);
if (!*locked) {
/* Continue to retry until we succeeded */
BUG_ON(ret != 0);
goto retry;
}
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
if (ret != 1) {
BUG_ON(ret > 1);
if (!pages_done)
pages_done = ret;
break;
}
nr_pages--;
pages_done++;
if (!nr_pages)
break;
mm/gup: continue VM_FAULT_RETRY processing even for pre-faults When get_user_pages*() is called with pages = NULL, the processing of VM_FAULT_RETRY terminates early without actually retrying to fault-in all the pages. If the pages in the requested range belong to a VMA that has userfaultfd registered, handle_userfault() returns VM_FAULT_RETRY *after* user space has populated the page, but for the gup pre-fault case there's no actual retry and the caller will get no pages although they are present. This issue was uncovered when running post-copy memory restore in CRIU after d9c9ce34ed5c ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails"). After this change, the copying of FPU state to the sigframe switched from copy_to_user() variants which caused a real page fault to get_user_pages() with pages parameter set to NULL. In post-copy mode of CRIU, the destination memory is managed with userfaultfd and lack of the retry for pre-fault case in get_user_pages() causes a crash of the restored process. Making the pre-fault behavior of get_user_pages() the same as the "normal" one fixes the issue. Link: http://lkml.kernel.org/r/1557844195-18882-1-git-send-email-rppt@linux.ibm.com Fixes: d9c9ce34ed5c ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails") Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Tested-by: Andrei Vagin <avagin@gmail.com> [https://travis-ci.org/avagin/linux/builds/533184940] Tested-by: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Borislav Petkov <bp@suse.de> Cc: Pavel Machek <pavel@ucw.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-06-01 13:30:33 +08:00
if (likely(pages))
pages++;
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
start += PAGE_SIZE;
}
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
if (must_unlock && *locked) {
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
/*
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
* We either temporarily dropped the lock, or the caller
* requested that we both acquire and drop the lock. Either way,
* we must now unlock, and notify the caller of that state.
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
*/
mmap locking API: use coccinelle to convert mmap_sem rwsem call sites This change converts the existing mmap_sem rwsem calls to use the new mmap locking API instead. The change is generated using coccinelle with the following rule: // spatch --sp-file mmap_lock_api.cocci --in-place --include-headers --dir . @@ expression mm; @@ ( -init_rwsem +mmap_init_lock | -down_write +mmap_write_lock | -down_write_killable +mmap_write_lock_killable | -down_write_trylock +mmap_write_trylock | -up_write +mmap_write_unlock | -downgrade_write +mmap_write_downgrade | -down_read +mmap_read_lock | -down_read_killable +mmap_read_lock_killable | -down_read_trylock +mmap_read_trylock | -up_read +mmap_read_unlock ) -(&mm->mmap_sem) +(mm) Signed-off-by: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jerome Glisse <jglisse@redhat.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Liam Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ying Han <yinghan@google.com> Link: http://lkml.kernel.org/r/20200520052908.204642-5-walken@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-09 12:33:25 +08:00
mmap_read_unlock(mm);
mm: gup: add get_user_pages_locked and get_user_pages_unlocked FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for reading to reduce the mmap_sem contention (for writing), like while waiting for I/O completion. The problem is that right now practically no get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging that nifty feature. Andres fixed it for the KVM page fault. However get_user_pages_fast remains uncovered, and 99% of other get_user_pages aren't using it either (the only exception being FOLL_NOWAIT in KVM which is really nonblocking and in fact it doesn't even release the mmap_sem). So this patchsets extends the optimization Andres did in the KVM page fault to the whole kernel. It makes most important places (including gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times during I/O. The only few places that remains uncovered are drivers like v4l and other exceptions that tends to work on their own memory and they're not working on random user memory (for example like O_DIRECT that uses gup_fast and is fully covered by this patch). A follow up patch should probably also add a printk_once warning to get_user_pages that should go obsolete and be phased out eventually. The "vmas" parameter of get_user_pages makes it fundamentally incompatible with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the mmap_sem is released). While this is just an optimization, this becomes an absolute requirement for the userfaultfd feature http://lwn.net/Articles/615086/ . The userfaultfd allows to block the page fault, and in order to do so I need to drop the mmap_sem first. So this patch also ensures that all memory where userfaultfd could be registered by KVM, the very first fault (no matter if it is a regular page fault, or a get_user_pages) always has FAULT_FOLL_ALLOW_RETRY set. Then the userfaultfd blocks and it is waken only when the pagetable is already mapped. The second fault attempt after the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry without it. This patch (of 5): We can leverage the VM_FAULT_RETRY functionality in the page fault paths better by using either get_user_pages_locked or get_user_pages_unlocked. The former allows conversion of get_user_pages invocations that will have to pass a "&locked" parameter to know if the mmap_sem was dropped during the call. Example from: down_read(&mm->mmap_sem); do_something() get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); to: int locked = 1; down_read(&mm->mmap_sem); do_something() get_user_pages_locked(tsk, mm, ..., pages, &locked); if (locked) up_read(&mm->mmap_sem); The latter is suitable only as a drop in replacement of the form: down_read(&mm->mmap_sem); get_user_pages(tsk, mm, ..., pages, NULL); up_read(&mm->mmap_sem); into: get_user_pages_unlocked(tsk, mm, ..., pages); Where tsk, mm, the intermediate "..." paramters and "pages" can be any value as before. Just the last parameter of get_user_pages (vmas) must be NULL for get_user_pages_locked|unlocked to be usable (the latter original form wouldn't have been safe anyway if vmas wasn't null, for the former we just make it explicit by dropping the parameter). If vmas is not NULL these two methods cannot be used. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by: Andres Lagar-Cavilla <andreslc@google.com> Reviewed-by: Peter Feiner <pfeiner@google.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 07:27:17 +08:00
*locked = 0;
}
return pages_done;
}
/**
* populate_vma_page_range() - populate a range of pages in the vma.
* @vma: target vma
* @start: start address
* @end: end address
* @locked: whether the mmap_lock is still held
*
* This takes care of mlocking the pages too if VM_LOCKED is set.
*
* Return either number of pages pinned in the vma, or a negative error
* code on error.
*
* vma->vm_mm->mmap_lock must be held.
*
mm/gup: rename "nonblocking" to "locked" where proper Patch series "mm: Page fault enhancements", v6. This series contains cleanups and enhancements to current page fault logic. The whole idea comes from the discussion between Andrea and Linus on the bug reported by syzbot here: https://lkml.org/lkml/2017/11/2/833 Basically it does two things: (a) Allows the page fault logic to be more interactive on not only SIGKILL, but also the rest of userspace signals, and, (b) Allows the page fault retry (VM_FAULT_RETRY) to happen for more than once. For (a): with the changes we should be able to react faster when page faults are working in parallel with userspace signals like SIGSTOP and SIGCONT (and more), and with that we can remove the buggy part in userfaultfd and benefit the whole page fault mechanism on faster signal processing to reach the userspace. For (b), we should be able to allow the page fault handler to loop for even more than twice. Some context: for now since we have FAULT_FLAG_ALLOW_RETRY we can allow to retry the page fault once with the same interrupt context, however never more than twice. This can be not only a potential cleanup to remove this assumption since AFAIU the code itself doesn't really have this twice-only limitation (though that should be a protective approach in the past), at the same time it'll greatly simplify future works like userfaultfd write-protect where it's possible to retry for more than twice (please have a look at [1] below for a possible user that might require the page fault to be handled for a third time; if we can remove the retry limitation we can simply drop that patch and those complexity). This patch (of 16): There's plenty of places around __get_user_pages() that has a parameter "nonblocking" which does not really mean that "it won't block" (because it can really block) but instead it shows whether the mmap_sem is released by up_read() during the page fault handling mostly when VM_FAULT_RETRY is returned. We have the correct naming in e.g. get_user_pages_locked() or get_user_pages_remote() as "locked", however there're still many places that are using the "nonblocking" as name. Renaming the places to "locked" where proper to better suite the functionality of the variable. While at it, fixing up some of the comments accordingly. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Martin Cracauer <cracauer@cons.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220155353.8676-2-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:07:58 +08:00
* If @locked is NULL, it may be held for read or write and will
* be unperturbed.
*
mm/gup: rename "nonblocking" to "locked" where proper Patch series "mm: Page fault enhancements", v6. This series contains cleanups and enhancements to current page fault logic. The whole idea comes from the discussion between Andrea and Linus on the bug reported by syzbot here: https://lkml.org/lkml/2017/11/2/833 Basically it does two things: (a) Allows the page fault logic to be more interactive on not only SIGKILL, but also the rest of userspace signals, and, (b) Allows the page fault retry (VM_FAULT_RETRY) to happen for more than once. For (a): with the changes we should be able to react faster when page faults are working in parallel with userspace signals like SIGSTOP and SIGCONT (and more), and with that we can remove the buggy part in userfaultfd and benefit the whole page fault mechanism on faster signal processing to reach the userspace. For (b), we should be able to allow the page fault handler to loop for even more than twice. Some context: for now since we have FAULT_FLAG_ALLOW_RETRY we can allow to retry the page fault once with the same interrupt context, however never more than twice. This can be not only a potential cleanup to remove this assumption since AFAIU the code itself doesn't really have this twice-only limitation (though that should be a protective approach in the past), at the same time it'll greatly simplify future works like userfaultfd write-protect where it's possible to retry for more than twice (please have a look at [1] below for a possible user that might require the page fault to be handled for a third time; if we can remove the retry limitation we can simply drop that patch and those complexity). This patch (of 16): There's plenty of places around __get_user_pages() that has a parameter "nonblocking" which does not really mean that "it won't block" (because it can really block) but instead it shows whether the mmap_sem is released by up_read() during the page fault handling mostly when VM_FAULT_RETRY is returned. We have the correct naming in e.g. get_user_pages_locked() or get_user_pages_remote() as "locked", however there're still many places that are using the "nonblocking" as name. Renaming the places to "locked" where proper to better suite the functionality of the variable. While at it, fixing up some of the comments accordingly. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Martin Cracauer <cracauer@cons.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220155353.8676-2-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:07:58 +08:00
* If @locked is non-NULL, it must held for read only and may be
* released. If it's released, *@locked will be set to 0.
*/
long populate_vma_page_range(struct vm_area_struct *vma,
mm/gup: rename "nonblocking" to "locked" where proper Patch series "mm: Page fault enhancements", v6. This series contains cleanups and enhancements to current page fault logic. The whole idea comes from the discussion between Andrea and Linus on the bug reported by syzbot here: https://lkml.org/lkml/2017/11/2/833 Basically it does two things: (a) Allows the page fault logic to be more interactive on not only SIGKILL, but also the rest of userspace signals, and, (b) Allows the page fault retry (VM_FAULT_RETRY) to happen for more than once. For (a): with the changes we should be able to react faster when page faults are working in parallel with userspace signals like SIGSTOP and SIGCONT (and more), and with that we can remove the buggy part in userfaultfd and benefit the whole page fault mechanism on faster signal processing to reach the userspace. For (b), we should be able to allow the page fault handler to loop for even more than twice. Some context: for now since we have FAULT_FLAG_ALLOW_RETRY we can allow to retry the page fault once with the same interrupt context, however never more than twice. This can be not only a potential cleanup to remove this assumption since AFAIU the code itself doesn't really have this twice-only limitation (though that should be a protective approach in the past), at the same time it'll greatly simplify future works like userfaultfd write-protect where it's possible to retry for more than twice (please have a look at [1] below for a possible user that might require the page fault to be handled for a third time; if we can remove the retry limitation we can simply drop that patch and those complexity). This patch (of 16): There's plenty of places around __get_user_pages() that has a parameter "nonblocking" which does not really mean that "it won't block" (because it can really block) but instead it shows whether the mmap_sem is released by up_read() during the page fault handling mostly when VM_FAULT_RETRY is returned. We have the correct naming in e.g. get_user_pages_locked() or get_user_pages_remote() as "locked", however there're still many places that are using the "nonblocking" as name. Renaming the places to "locked" where proper to better suite the functionality of the variable. While at it, fixing up some of the comments accordingly. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Martin Cracauer <cracauer@cons.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220155353.8676-2-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:07:58 +08:00
unsigned long start, unsigned long end, int *locked)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long nr_pages = (end - start) / PAGE_SIZE;
int local_locked = 1;
int gup_flags;
mm/munlock: add lru_add_drain() to fix memcg_stat_test Mike reports that LTP memcg_stat_test usually leads to memcg_stat_test 3 TINFO: Test unevictable with MAP_LOCKED memcg_stat_test 3 TINFO: Running memcg_process --mmap-lock1 -s 135168 memcg_stat_test 3 TINFO: Warming up pid: 3460 memcg_stat_test 3 TINFO: Process is still here after warm up: 3460 memcg_stat_test 3 TFAIL: unevictable is 122880, 135168 expected but may also lead to memcg_stat_test 4 TINFO: Test unevictable with mlock memcg_stat_test 4 TINFO: Running memcg_process --mmap-lock2 -s 135168 memcg_stat_test 4 TINFO: Warming up pid: 4271 memcg_stat_test 4 TINFO: Process is still here after warm up: 4271 memcg_stat_test 4 TFAIL: unevictable is 122880, 135168 expected or both. A wee bit flaky. follow_page_pte() used to have an lru_add_drain() per each page mlocked, and the test came to rely on accurate stats. The pagevec to be drained is different now, but still covered by lru_add_drain(); and, never mind the test, I believe it's in everyone's interest that a bulk faulting interface like populate_vma_page_range() or faultin_vma_page_range() should drain its local pagevecs at the end, to save others sometimes needing the much more expensive lru_add_drain_all(). This does not absolutely guarantee exact stats - the mlocking task can be migrated between CPUs as it proceeds - but it's good enough and the tests pass. Link: https://lkml.kernel.org/r/47f6d39c-a075-50cb-1cfb-26dd957a48af@google.com Fixes: b67bf49ce7aa ("mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE") Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Mike Galbraith <efault@gmx.de> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-04-02 02:28:27 +08:00
long ret;
VM_BUG_ON(!PAGE_ALIGNED(start));
VM_BUG_ON(!PAGE_ALIGNED(end));
VM_BUG_ON_VMA(start < vma->vm_start, vma);
VM_BUG_ON_VMA(end > vma->vm_end, vma);
mmap_assert_locked(mm);
/*
* Rightly or wrongly, the VM_LOCKONFAULT case has never used
* faultin_page() to break COW, so it has no work to do here.
*/
if (vma->vm_flags & VM_LOCKONFAULT)
return nr_pages;
gup_flags = FOLL_TOUCH;
/*
* We want to touch writable mappings with a write fault in order
* to break COW, except for shared mappings because these don't COW
* and we would not want to dirty them for nothing.
*/
if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
gup_flags |= FOLL_WRITE;
/*
* We want mlock to succeed for regions that have any permissions
* other than PROT_NONE.
*/
mm/vma: make vma_is_accessible() available for general use Lets move vma_is_accessible() helper to include/linux/mm.h which makes it available for general use. While here, this replaces all remaining open encodings for VMA access check with vma_is_accessible(). Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Acked-by: Guo Ren <guoren@kernel.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Guo Ren <guoren@kernel.org> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Paul Burton <paulburton@kernel.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Rich Felker <dalias@libc.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Nick Piggin <npiggin@gmail.com> Cc: Paul Mackerras <paulus@ozlabs.org> Cc: Will Deacon <will@kernel.org> Link: http://lkml.kernel.org/r/1582520593-30704-3-git-send-email-anshuman.khandual@arm.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-07 11:03:47 +08:00
if (vma_is_accessible(vma))
gup_flags |= FOLL_FORCE;
if (locked)
gup_flags |= FOLL_UNLOCKABLE;
/*
* We made sure addr is within a VMA, so the following will
* not result in a stack expansion that recurses back here.
*/
mm/munlock: add lru_add_drain() to fix memcg_stat_test Mike reports that LTP memcg_stat_test usually leads to memcg_stat_test 3 TINFO: Test unevictable with MAP_LOCKED memcg_stat_test 3 TINFO: Running memcg_process --mmap-lock1 -s 135168 memcg_stat_test 3 TINFO: Warming up pid: 3460 memcg_stat_test 3 TINFO: Process is still here after warm up: 3460 memcg_stat_test 3 TFAIL: unevictable is 122880, 135168 expected but may also lead to memcg_stat_test 4 TINFO: Test unevictable with mlock memcg_stat_test 4 TINFO: Running memcg_process --mmap-lock2 -s 135168 memcg_stat_test 4 TINFO: Warming up pid: 4271 memcg_stat_test 4 TINFO: Process is still here after warm up: 4271 memcg_stat_test 4 TFAIL: unevictable is 122880, 135168 expected or both. A wee bit flaky. follow_page_pte() used to have an lru_add_drain() per each page mlocked, and the test came to rely on accurate stats. The pagevec to be drained is different now, but still covered by lru_add_drain(); and, never mind the test, I believe it's in everyone's interest that a bulk faulting interface like populate_vma_page_range() or faultin_vma_page_range() should drain its local pagevecs at the end, to save others sometimes needing the much more expensive lru_add_drain_all(). This does not absolutely guarantee exact stats - the mlocking task can be migrated between CPUs as it proceeds - but it's good enough and the tests pass. Link: https://lkml.kernel.org/r/47f6d39c-a075-50cb-1cfb-26dd957a48af@google.com Fixes: b67bf49ce7aa ("mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE") Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Mike Galbraith <efault@gmx.de> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-04-02 02:28:27 +08:00
ret = __get_user_pages(mm, start, nr_pages, gup_flags,
NULL, NULL, locked ? locked : &local_locked);
mm/munlock: add lru_add_drain() to fix memcg_stat_test Mike reports that LTP memcg_stat_test usually leads to memcg_stat_test 3 TINFO: Test unevictable with MAP_LOCKED memcg_stat_test 3 TINFO: Running memcg_process --mmap-lock1 -s 135168 memcg_stat_test 3 TINFO: Warming up pid: 3460 memcg_stat_test 3 TINFO: Process is still here after warm up: 3460 memcg_stat_test 3 TFAIL: unevictable is 122880, 135168 expected but may also lead to memcg_stat_test 4 TINFO: Test unevictable with mlock memcg_stat_test 4 TINFO: Running memcg_process --mmap-lock2 -s 135168 memcg_stat_test 4 TINFO: Warming up pid: 4271 memcg_stat_test 4 TINFO: Process is still here after warm up: 4271 memcg_stat_test 4 TFAIL: unevictable is 122880, 135168 expected or both. A wee bit flaky. follow_page_pte() used to have an lru_add_drain() per each page mlocked, and the test came to rely on accurate stats. The pagevec to be drained is different now, but still covered by lru_add_drain(); and, never mind the test, I believe it's in everyone's interest that a bulk faulting interface like populate_vma_page_range() or faultin_vma_page_range() should drain its local pagevecs at the end, to save others sometimes needing the much more expensive lru_add_drain_all(). This does not absolutely guarantee exact stats - the mlocking task can be migrated between CPUs as it proceeds - but it's good enough and the tests pass. Link: https://lkml.kernel.org/r/47f6d39c-a075-50cb-1cfb-26dd957a48af@google.com Fixes: b67bf49ce7aa ("mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE") Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Mike Galbraith <efault@gmx.de> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-04-02 02:28:27 +08:00
lru_add_drain();
return ret;
}
mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables I. Background: Sparse Memory Mappings When we manage sparse memory mappings dynamically in user space - also sometimes involving MAP_NORESERVE - we want to dynamically populate/ discard memory inside such a sparse memory region. Example users are hypervisors (especially implementing memory ballooning or similar technologies like virtio-mem) and memory allocators. In addition, we want to fail in a nice way (instead of generating SIGBUS) if populating does not succeed because we are out of backend memory (which can happen easily with file-based mappings, especially tmpfs and hugetlbfs). While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for reliably discarding memory for most mapping types, there is no generic approach to populate page tables and preallocate memory. Although mmap() supports MAP_POPULATE, it is not applicable to the concept of sparse memory mappings, where we want to populate/discard dynamically and avoid expensive/problematic remappings. In addition, we never actually report errors during the final populate phase - it is best-effort only. fallocate() can be used to preallocate file-based memory and fail in a safe way. However, it cannot really be used for any private mappings on anonymous files via memfd due to COW semantics. In addition, fallocate() does not actually populate page tables, so we still always get pagefaults on first access - which is sometimes undesired (i.e., real-time workloads) and requires real prefaulting of page tables, not just a preallocation of backend storage. There might be interesting use cases for sparse memory regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy as it does not prefault page tables. II. On preallcoation/prefaulting from user space Because we don't have a proper interface, what applications (like QEMU and databases) end up doing is touching (i.e., reading+writing one byte to not overwrite existing data) all individual pages. However, that approach 1) Can result in wear on storage backing, because we end up reading/writing each page; this is especially a problem for dax/pmem. 2) Can result in mmap_sem contention when prefaulting via multiple threads. 3) Requires expensive signal handling, especially to catch SIGBUS in case of hugetlbfs/shmem/file-backed memory. For example, this is problematic in hypervisors like QEMU where SIGBUS handlers might already be used by other subsystems concurrently to e.g, handle hardware errors. "Simply" doing preallocation concurrently from other thread is not that easy. III. On MADV_WILLNEED Extending MADV_WILLNEED is not an option because 1. It would change the semantics: "Expect access in the near future." and "might be a good idea to read some pages" vs. "Definitely populate/ preallocate all memory and definitely fail on errors.". 2. Existing users (like virtio-balloon in QEMU when deflating the balloon) don't want populate/prealloc semantics. They treat this rather as a hint to give a little performance boost without too much overhead - and don't expect that a lot of memory might get consumed or a lot of time might be spent. IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by MAP_POPULATE, with the following semantics: 1. MADV_POPULATE_READ can be used to prefault page tables just like manually reading each individual page. This will not break any COW mappings. The shared zero page might get mapped and no backend storage might get preallocated -- allocation might be deferred to write-fault time. Especially shared file mappings require an explicit fallocate() upfront to actually preallocate backend memory (blocks in the file system) in case the file might have holes. 2. If MADV_POPULATE_READ succeeds, all page tables have been populated (prefaulted) readable once. 3. MADV_POPULATE_WRITE can be used to preallocate backend memory and prefault page tables just like manually writing (or reading+writing) each individual page. This will break any COW mappings -- e.g., the shared zeropage is never populated. 4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated (prefaulted) writable once. 5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special mappings marked with VM_PFNMAP and VM_IO. Also, proper access permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such mapping is encountered, madvise() fails with -EINVAL. 6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables might have been populated. 7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON when encountering a HW poisoned page in the range. 8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot protect from the OOM (Out Of Memory) handler killing the process. While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e., preallocate memory and prefault page tables for VMs), one issue is that whenever we prefault pages writable, the pages have to be marked dirty, because the CPU could dirty them any time. while not a real problem for hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each page will be marked dirty and has to be written back later when evicting. MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole mapping from backend storage without marking it dirty, such that eviction won't have to write it back. As discussed above, shared file mappings might require an explciit fallocate() upfront to achieve preallcoation+prepopulation. Although sparse memory mappings are the primary use case, this will also be useful for other preallocate/prefault use cases where MAP_POPULATE is not desired or the semantics of MAP_POPULATE are not sufficient: as one example, QEMU users can trigger preallocation/prefaulting of guest RAM after the mapping was created -- and don't want errors to be silently suppressed. Looking at the history, MADV_POPULATE was already proposed in 2013 [1], however, the main motivation back than was performance improvements -- which should also still be the case. V. Single-threaded performance comparison I did a short experiment, prefaulting page tables on completely *empty mappings/files* and repeated the experiment 10 times. The results correspond to the shortest execution time. In general, the performance benefit for huge pages is negligible with small mappings. V.1: Private mappings POPULATE_READ and POPULATE_WRITE is fastest. Note that Reading/POPULATE_READ will populate the shared zeropage where applicable -- which result in short population times. The fastest way to allocate backend storage (here: swap or huge pages) and prefault page tables is POPULATE_WRITE. V.2: Shared mappings fallocate() is fastest, however, doesn't prefault page tables. POPULATE_WRITE is faster than simple writes and read/writes. POPULATE_READ is faster than simple reads. Without a fd, the fastest way to allocate backend storage and prefault page tables is POPULATE_WRITE. With an fd, the fastest way is usually FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one exception are actual files: FALLOCATE+Read is slightly faster than FALLOCATE+POPULATE_READ. The fastest way to allocate backend storage prefault page tables is FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then, FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as dirty. v.3: Detailed results ================================================== 2 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 0.119 ms Anon 4 KiB : Write : 0.222 ms Anon 4 KiB : Read/Write : 0.380 ms Anon 4 KiB : POPULATE_READ : 0.060 ms Anon 4 KiB : POPULATE_WRITE : 0.158 ms Memfd 4 KiB : Read : 0.034 ms Memfd 4 KiB : Write : 0.310 ms Memfd 4 KiB : Read/Write : 0.362 ms Memfd 4 KiB : POPULATE_READ : 0.039 ms Memfd 4 KiB : POPULATE_WRITE : 0.229 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.033 ms tmpfs : Write : 0.313 ms tmpfs : Read/Write : 0.406 ms tmpfs : POPULATE_READ : 0.039 ms tmpfs : POPULATE_WRITE : 0.285 ms file : Read : 0.033 ms file : Write : 0.351 ms file : Read/Write : 0.408 ms file : POPULATE_READ : 0.039 ms file : POPULATE_WRITE : 0.290 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 237.940 ms Anon 4 KiB : Write : 708.409 ms Anon 4 KiB : Read/Write : 1054.041 ms Anon 4 KiB : POPULATE_READ : 124.310 ms Anon 4 KiB : POPULATE_WRITE : 572.582 ms Memfd 4 KiB : Read : 136.928 ms Memfd 4 KiB : Write : 963.898 ms Memfd 4 KiB : Read/Write : 1106.561 ms Memfd 4 KiB : POPULATE_READ : 78.450 ms Memfd 4 KiB : POPULATE_WRITE : 805.881 ms Memfd 2 MiB : Read : 357.116 ms Memfd 2 MiB : Write : 357.210 ms Memfd 2 MiB : Read/Write : 357.606 ms Memfd 2 MiB : POPULATE_READ : 356.094 ms Memfd 2 MiB : POPULATE_WRITE : 356.937 ms tmpfs : Read : 137.536 ms tmpfs : Write : 954.362 ms tmpfs : Read/Write : 1105.954 ms tmpfs : POPULATE_READ : 80.289 ms tmpfs : POPULATE_WRITE : 822.826 ms file : Read : 137.874 ms file : Write : 987.025 ms file : Read/Write : 1107.439 ms file : POPULATE_READ : 80.413 ms file : POPULATE_WRITE : 857.622 ms hugetlbfs : Read : 355.607 ms hugetlbfs : Write : 355.729 ms hugetlbfs : Read/Write : 356.127 ms hugetlbfs : POPULATE_READ : 354.585 ms hugetlbfs : POPULATE_WRITE : 355.138 ms ************************************************** 2 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 0.394 ms Anon 4 KiB : Write : 0.348 ms Anon 4 KiB : Read/Write : 0.400 ms Anon 4 KiB : POPULATE_READ : 0.326 ms Anon 4 KiB : POPULATE_WRITE : 0.273 ms Anon 2 MiB : Read : 0.030 ms Anon 2 MiB : Write : 0.030 ms Anon 2 MiB : Read/Write : 0.030 ms Anon 2 MiB : POPULATE_READ : 0.030 ms Anon 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 4 KiB : Read : 0.412 ms Memfd 4 KiB : Write : 0.372 ms Memfd 4 KiB : Read/Write : 0.419 ms Memfd 4 KiB : POPULATE_READ : 0.343 ms Memfd 4 KiB : POPULATE_WRITE : 0.288 ms Memfd 4 KiB : FALLOCATE : 0.137 ms Memfd 4 KiB : FALLOCATE+Read : 0.446 ms Memfd 4 KiB : FALLOCATE+Write : 0.330 ms Memfd 4 KiB : FALLOCATE+Read/Write : 0.454 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 0.379 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 0.268 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 2 MiB : FALLOCATE : 0.030 ms Memfd 2 MiB : FALLOCATE+Read : 0.031 ms Memfd 2 MiB : FALLOCATE+Write : 0.031 ms Memfd 2 MiB : FALLOCATE+Read/Write : 0.031 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 0.030 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.416 ms tmpfs : Write : 0.369 ms tmpfs : Read/Write : 0.425 ms tmpfs : POPULATE_READ : 0.346 ms tmpfs : POPULATE_WRITE : 0.295 ms tmpfs : FALLOCATE : 0.139 ms tmpfs : FALLOCATE+Read : 0.447 ms tmpfs : FALLOCATE+Write : 0.333 ms tmpfs : FALLOCATE+Read/Write : 0.454 ms tmpfs : FALLOCATE+POPULATE_READ : 0.380 ms tmpfs : FALLOCATE+POPULATE_WRITE : 0.272 ms file : Read : 0.191 ms file : Write : 0.511 ms file : Read/Write : 0.524 ms file : POPULATE_READ : 0.196 ms file : POPULATE_WRITE : 0.434 ms file : FALLOCATE : 0.004 ms file : FALLOCATE+Read : 0.197 ms file : FALLOCATE+Write : 0.554 ms file : FALLOCATE+Read/Write : 0.480 ms file : FALLOCATE+POPULATE_READ : 0.201 ms file : FALLOCATE+POPULATE_WRITE : 0.381 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms hugetlbfs : FALLOCATE : 0.030 ms hugetlbfs : FALLOCATE+Read : 0.031 ms hugetlbfs : FALLOCATE+Write : 0.031 ms hugetlbfs : FALLOCATE+Read/Write : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_READ : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 1053.090 ms Anon 4 KiB : Write : 913.642 ms Anon 4 KiB : Read/Write : 1060.350 ms Anon 4 KiB : POPULATE_READ : 893.691 ms Anon 4 KiB : POPULATE_WRITE : 782.885 ms Anon 2 MiB : Read : 358.553 ms Anon 2 MiB : Write : 358.419 ms Anon 2 MiB : Read/Write : 357.992 ms Anon 2 MiB : POPULATE_READ : 357.533 ms Anon 2 MiB : POPULATE_WRITE : 357.808 ms Memfd 4 KiB : Read : 1078.144 ms Memfd 4 KiB : Write : 942.036 ms Memfd 4 KiB : Read/Write : 1100.391 ms Memfd 4 KiB : POPULATE_READ : 925.829 ms Memfd 4 KiB : POPULATE_WRITE : 804.394 ms Memfd 4 KiB : FALLOCATE : 304.632 ms Memfd 4 KiB : FALLOCATE+Read : 1163.359 ms Memfd 4 KiB : FALLOCATE+Write : 933.186 ms Memfd 4 KiB : FALLOCATE+Read/Write : 1187.304 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 1013.660 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 794.560 ms Memfd 2 MiB : Read : 358.131 ms Memfd 2 MiB : Write : 358.099 ms Memfd 2 MiB : Read/Write : 358.250 ms Memfd 2 MiB : POPULATE_READ : 357.563 ms Memfd 2 MiB : POPULATE_WRITE : 357.334 ms Memfd 2 MiB : FALLOCATE : 356.735 ms Memfd 2 MiB : FALLOCATE+Read : 358.152 ms Memfd 2 MiB : FALLOCATE+Write : 358.331 ms Memfd 2 MiB : FALLOCATE+Read/Write : 358.018 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 357.286 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 357.523 ms tmpfs : Read : 1087.265 ms tmpfs : Write : 950.840 ms tmpfs : Read/Write : 1107.567 ms tmpfs : POPULATE_READ : 922.605 ms tmpfs : POPULATE_WRITE : 810.094 ms tmpfs : FALLOCATE : 306.320 ms tmpfs : FALLOCATE+Read : 1169.796 ms tmpfs : FALLOCATE+Write : 933.730 ms tmpfs : FALLOCATE+Read/Write : 1191.610 ms tmpfs : FALLOCATE+POPULATE_READ : 1020.474 ms tmpfs : FALLOCATE+POPULATE_WRITE : 798.945 ms file : Read : 654.101 ms file : Write : 1259.142 ms file : Read/Write : 1289.509 ms file : POPULATE_READ : 661.642 ms file : POPULATE_WRITE : 1106.816 ms file : FALLOCATE : 1.864 ms file : FALLOCATE+Read : 656.328 ms file : FALLOCATE+Write : 1153.300 ms file : FALLOCATE+Read/Write : 1180.613 ms file : FALLOCATE+POPULATE_READ : 668.347 ms file : FALLOCATE+POPULATE_WRITE : 996.143 ms hugetlbfs : Read : 357.245 ms hugetlbfs : Write : 357.413 ms hugetlbfs : Read/Write : 357.120 ms hugetlbfs : POPULATE_READ : 356.321 ms hugetlbfs : POPULATE_WRITE : 356.693 ms hugetlbfs : FALLOCATE : 355.927 ms hugetlbfs : FALLOCATE+Read : 357.074 ms hugetlbfs : FALLOCATE+Write : 357.120 ms hugetlbfs : FALLOCATE+Read/Write : 356.983 ms hugetlbfs : FALLOCATE+POPULATE_READ : 356.413 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 356.266 ms ************************************************** [1] https://lkml.org/lkml/2013/6/27/698 [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 09:52:28 +08:00
/*
* faultin_vma_page_range() - populate (prefault) page tables inside the
* given VMA range readable/writable
*
* This takes care of mlocking the pages, too, if VM_LOCKED is set.
*
* @vma: target vma
* @start: start address
* @end: end address
* @write: whether to prefault readable or writable
* @locked: whether the mmap_lock is still held
*
* Returns either number of processed pages in the vma, or a negative error
* code on error (see __get_user_pages()).
*
* vma->vm_mm->mmap_lock must be held. The range must be page-aligned and
* covered by the VMA. If it's released, *@locked will be set to 0.
mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables I. Background: Sparse Memory Mappings When we manage sparse memory mappings dynamically in user space - also sometimes involving MAP_NORESERVE - we want to dynamically populate/ discard memory inside such a sparse memory region. Example users are hypervisors (especially implementing memory ballooning or similar technologies like virtio-mem) and memory allocators. In addition, we want to fail in a nice way (instead of generating SIGBUS) if populating does not succeed because we are out of backend memory (which can happen easily with file-based mappings, especially tmpfs and hugetlbfs). While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for reliably discarding memory for most mapping types, there is no generic approach to populate page tables and preallocate memory. Although mmap() supports MAP_POPULATE, it is not applicable to the concept of sparse memory mappings, where we want to populate/discard dynamically and avoid expensive/problematic remappings. In addition, we never actually report errors during the final populate phase - it is best-effort only. fallocate() can be used to preallocate file-based memory and fail in a safe way. However, it cannot really be used for any private mappings on anonymous files via memfd due to COW semantics. In addition, fallocate() does not actually populate page tables, so we still always get pagefaults on first access - which is sometimes undesired (i.e., real-time workloads) and requires real prefaulting of page tables, not just a preallocation of backend storage. There might be interesting use cases for sparse memory regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy as it does not prefault page tables. II. On preallcoation/prefaulting from user space Because we don't have a proper interface, what applications (like QEMU and databases) end up doing is touching (i.e., reading+writing one byte to not overwrite existing data) all individual pages. However, that approach 1) Can result in wear on storage backing, because we end up reading/writing each page; this is especially a problem for dax/pmem. 2) Can result in mmap_sem contention when prefaulting via multiple threads. 3) Requires expensive signal handling, especially to catch SIGBUS in case of hugetlbfs/shmem/file-backed memory. For example, this is problematic in hypervisors like QEMU where SIGBUS handlers might already be used by other subsystems concurrently to e.g, handle hardware errors. "Simply" doing preallocation concurrently from other thread is not that easy. III. On MADV_WILLNEED Extending MADV_WILLNEED is not an option because 1. It would change the semantics: "Expect access in the near future." and "might be a good idea to read some pages" vs. "Definitely populate/ preallocate all memory and definitely fail on errors.". 2. Existing users (like virtio-balloon in QEMU when deflating the balloon) don't want populate/prealloc semantics. They treat this rather as a hint to give a little performance boost without too much overhead - and don't expect that a lot of memory might get consumed or a lot of time might be spent. IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by MAP_POPULATE, with the following semantics: 1. MADV_POPULATE_READ can be used to prefault page tables just like manually reading each individual page. This will not break any COW mappings. The shared zero page might get mapped and no backend storage might get preallocated -- allocation might be deferred to write-fault time. Especially shared file mappings require an explicit fallocate() upfront to actually preallocate backend memory (blocks in the file system) in case the file might have holes. 2. If MADV_POPULATE_READ succeeds, all page tables have been populated (prefaulted) readable once. 3. MADV_POPULATE_WRITE can be used to preallocate backend memory and prefault page tables just like manually writing (or reading+writing) each individual page. This will break any COW mappings -- e.g., the shared zeropage is never populated. 4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated (prefaulted) writable once. 5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special mappings marked with VM_PFNMAP and VM_IO. Also, proper access permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such mapping is encountered, madvise() fails with -EINVAL. 6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables might have been populated. 7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON when encountering a HW poisoned page in the range. 8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot protect from the OOM (Out Of Memory) handler killing the process. While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e., preallocate memory and prefault page tables for VMs), one issue is that whenever we prefault pages writable, the pages have to be marked dirty, because the CPU could dirty them any time. while not a real problem for hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each page will be marked dirty and has to be written back later when evicting. MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole mapping from backend storage without marking it dirty, such that eviction won't have to write it back. As discussed above, shared file mappings might require an explciit fallocate() upfront to achieve preallcoation+prepopulation. Although sparse memory mappings are the primary use case, this will also be useful for other preallocate/prefault use cases where MAP_POPULATE is not desired or the semantics of MAP_POPULATE are not sufficient: as one example, QEMU users can trigger preallocation/prefaulting of guest RAM after the mapping was created -- and don't want errors to be silently suppressed. Looking at the history, MADV_POPULATE was already proposed in 2013 [1], however, the main motivation back than was performance improvements -- which should also still be the case. V. Single-threaded performance comparison I did a short experiment, prefaulting page tables on completely *empty mappings/files* and repeated the experiment 10 times. The results correspond to the shortest execution time. In general, the performance benefit for huge pages is negligible with small mappings. V.1: Private mappings POPULATE_READ and POPULATE_WRITE is fastest. Note that Reading/POPULATE_READ will populate the shared zeropage where applicable -- which result in short population times. The fastest way to allocate backend storage (here: swap or huge pages) and prefault page tables is POPULATE_WRITE. V.2: Shared mappings fallocate() is fastest, however, doesn't prefault page tables. POPULATE_WRITE is faster than simple writes and read/writes. POPULATE_READ is faster than simple reads. Without a fd, the fastest way to allocate backend storage and prefault page tables is POPULATE_WRITE. With an fd, the fastest way is usually FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one exception are actual files: FALLOCATE+Read is slightly faster than FALLOCATE+POPULATE_READ. The fastest way to allocate backend storage prefault page tables is FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then, FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as dirty. v.3: Detailed results ================================================== 2 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 0.119 ms Anon 4 KiB : Write : 0.222 ms Anon 4 KiB : Read/Write : 0.380 ms Anon 4 KiB : POPULATE_READ : 0.060 ms Anon 4 KiB : POPULATE_WRITE : 0.158 ms Memfd 4 KiB : Read : 0.034 ms Memfd 4 KiB : Write : 0.310 ms Memfd 4 KiB : Read/Write : 0.362 ms Memfd 4 KiB : POPULATE_READ : 0.039 ms Memfd 4 KiB : POPULATE_WRITE : 0.229 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.033 ms tmpfs : Write : 0.313 ms tmpfs : Read/Write : 0.406 ms tmpfs : POPULATE_READ : 0.039 ms tmpfs : POPULATE_WRITE : 0.285 ms file : Read : 0.033 ms file : Write : 0.351 ms file : Read/Write : 0.408 ms file : POPULATE_READ : 0.039 ms file : POPULATE_WRITE : 0.290 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 237.940 ms Anon 4 KiB : Write : 708.409 ms Anon 4 KiB : Read/Write : 1054.041 ms Anon 4 KiB : POPULATE_READ : 124.310 ms Anon 4 KiB : POPULATE_WRITE : 572.582 ms Memfd 4 KiB : Read : 136.928 ms Memfd 4 KiB : Write : 963.898 ms Memfd 4 KiB : Read/Write : 1106.561 ms Memfd 4 KiB : POPULATE_READ : 78.450 ms Memfd 4 KiB : POPULATE_WRITE : 805.881 ms Memfd 2 MiB : Read : 357.116 ms Memfd 2 MiB : Write : 357.210 ms Memfd 2 MiB : Read/Write : 357.606 ms Memfd 2 MiB : POPULATE_READ : 356.094 ms Memfd 2 MiB : POPULATE_WRITE : 356.937 ms tmpfs : Read : 137.536 ms tmpfs : Write : 954.362 ms tmpfs : Read/Write : 1105.954 ms tmpfs : POPULATE_READ : 80.289 ms tmpfs : POPULATE_WRITE : 822.826 ms file : Read : 137.874 ms file : Write : 987.025 ms file : Read/Write : 1107.439 ms file : POPULATE_READ : 80.413 ms file : POPULATE_WRITE : 857.622 ms hugetlbfs : Read : 355.607 ms hugetlbfs : Write : 355.729 ms hugetlbfs : Read/Write : 356.127 ms hugetlbfs : POPULATE_READ : 354.585 ms hugetlbfs : POPULATE_WRITE : 355.138 ms ************************************************** 2 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 0.394 ms Anon 4 KiB : Write : 0.348 ms Anon 4 KiB : Read/Write : 0.400 ms Anon 4 KiB : POPULATE_READ : 0.326 ms Anon 4 KiB : POPULATE_WRITE : 0.273 ms Anon 2 MiB : Read : 0.030 ms Anon 2 MiB : Write : 0.030 ms Anon 2 MiB : Read/Write : 0.030 ms Anon 2 MiB : POPULATE_READ : 0.030 ms Anon 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 4 KiB : Read : 0.412 ms Memfd 4 KiB : Write : 0.372 ms Memfd 4 KiB : Read/Write : 0.419 ms Memfd 4 KiB : POPULATE_READ : 0.343 ms Memfd 4 KiB : POPULATE_WRITE : 0.288 ms Memfd 4 KiB : FALLOCATE : 0.137 ms Memfd 4 KiB : FALLOCATE+Read : 0.446 ms Memfd 4 KiB : FALLOCATE+Write : 0.330 ms Memfd 4 KiB : FALLOCATE+Read/Write : 0.454 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 0.379 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 0.268 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 2 MiB : FALLOCATE : 0.030 ms Memfd 2 MiB : FALLOCATE+Read : 0.031 ms Memfd 2 MiB : FALLOCATE+Write : 0.031 ms Memfd 2 MiB : FALLOCATE+Read/Write : 0.031 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 0.030 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.416 ms tmpfs : Write : 0.369 ms tmpfs : Read/Write : 0.425 ms tmpfs : POPULATE_READ : 0.346 ms tmpfs : POPULATE_WRITE : 0.295 ms tmpfs : FALLOCATE : 0.139 ms tmpfs : FALLOCATE+Read : 0.447 ms tmpfs : FALLOCATE+Write : 0.333 ms tmpfs : FALLOCATE+Read/Write : 0.454 ms tmpfs : FALLOCATE+POPULATE_READ : 0.380 ms tmpfs : FALLOCATE+POPULATE_WRITE : 0.272 ms file : Read : 0.191 ms file : Write : 0.511 ms file : Read/Write : 0.524 ms file : POPULATE_READ : 0.196 ms file : POPULATE_WRITE : 0.434 ms file : FALLOCATE : 0.004 ms file : FALLOCATE+Read : 0.197 ms file : FALLOCATE+Write : 0.554 ms file : FALLOCATE+Read/Write : 0.480 ms file : FALLOCATE+POPULATE_READ : 0.201 ms file : FALLOCATE+POPULATE_WRITE : 0.381 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms hugetlbfs : FALLOCATE : 0.030 ms hugetlbfs : FALLOCATE+Read : 0.031 ms hugetlbfs : FALLOCATE+Write : 0.031 ms hugetlbfs : FALLOCATE+Read/Write : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_READ : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 1053.090 ms Anon 4 KiB : Write : 913.642 ms Anon 4 KiB : Read/Write : 1060.350 ms Anon 4 KiB : POPULATE_READ : 893.691 ms Anon 4 KiB : POPULATE_WRITE : 782.885 ms Anon 2 MiB : Read : 358.553 ms Anon 2 MiB : Write : 358.419 ms Anon 2 MiB : Read/Write : 357.992 ms Anon 2 MiB : POPULATE_READ : 357.533 ms Anon 2 MiB : POPULATE_WRITE : 357.808 ms Memfd 4 KiB : Read : 1078.144 ms Memfd 4 KiB : Write : 942.036 ms Memfd 4 KiB : Read/Write : 1100.391 ms Memfd 4 KiB : POPULATE_READ : 925.829 ms Memfd 4 KiB : POPULATE_WRITE : 804.394 ms Memfd 4 KiB : FALLOCATE : 304.632 ms Memfd 4 KiB : FALLOCATE+Read : 1163.359 ms Memfd 4 KiB : FALLOCATE+Write : 933.186 ms Memfd 4 KiB : FALLOCATE+Read/Write : 1187.304 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 1013.660 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 794.560 ms Memfd 2 MiB : Read : 358.131 ms Memfd 2 MiB : Write : 358.099 ms Memfd 2 MiB : Read/Write : 358.250 ms Memfd 2 MiB : POPULATE_READ : 357.563 ms Memfd 2 MiB : POPULATE_WRITE : 357.334 ms Memfd 2 MiB : FALLOCATE : 356.735 ms Memfd 2 MiB : FALLOCATE+Read : 358.152 ms Memfd 2 MiB : FALLOCATE+Write : 358.331 ms Memfd 2 MiB : FALLOCATE+Read/Write : 358.018 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 357.286 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 357.523 ms tmpfs : Read : 1087.265 ms tmpfs : Write : 950.840 ms tmpfs : Read/Write : 1107.567 ms tmpfs : POPULATE_READ : 922.605 ms tmpfs : POPULATE_WRITE : 810.094 ms tmpfs : FALLOCATE : 306.320 ms tmpfs : FALLOCATE+Read : 1169.796 ms tmpfs : FALLOCATE+Write : 933.730 ms tmpfs : FALLOCATE+Read/Write : 1191.610 ms tmpfs : FALLOCATE+POPULATE_READ : 1020.474 ms tmpfs : FALLOCATE+POPULATE_WRITE : 798.945 ms file : Read : 654.101 ms file : Write : 1259.142 ms file : Read/Write : 1289.509 ms file : POPULATE_READ : 661.642 ms file : POPULATE_WRITE : 1106.816 ms file : FALLOCATE : 1.864 ms file : FALLOCATE+Read : 656.328 ms file : FALLOCATE+Write : 1153.300 ms file : FALLOCATE+Read/Write : 1180.613 ms file : FALLOCATE+POPULATE_READ : 668.347 ms file : FALLOCATE+POPULATE_WRITE : 996.143 ms hugetlbfs : Read : 357.245 ms hugetlbfs : Write : 357.413 ms hugetlbfs : Read/Write : 357.120 ms hugetlbfs : POPULATE_READ : 356.321 ms hugetlbfs : POPULATE_WRITE : 356.693 ms hugetlbfs : FALLOCATE : 355.927 ms hugetlbfs : FALLOCATE+Read : 357.074 ms hugetlbfs : FALLOCATE+Write : 357.120 ms hugetlbfs : FALLOCATE+Read/Write : 356.983 ms hugetlbfs : FALLOCATE+POPULATE_READ : 356.413 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 356.266 ms ************************************************** [1] https://lkml.org/lkml/2013/6/27/698 [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 09:52:28 +08:00
*/
long faultin_vma_page_range(struct vm_area_struct *vma, unsigned long start,
unsigned long end, bool write, int *locked)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long nr_pages = (end - start) / PAGE_SIZE;
int gup_flags;
mm/munlock: add lru_add_drain() to fix memcg_stat_test Mike reports that LTP memcg_stat_test usually leads to memcg_stat_test 3 TINFO: Test unevictable with MAP_LOCKED memcg_stat_test 3 TINFO: Running memcg_process --mmap-lock1 -s 135168 memcg_stat_test 3 TINFO: Warming up pid: 3460 memcg_stat_test 3 TINFO: Process is still here after warm up: 3460 memcg_stat_test 3 TFAIL: unevictable is 122880, 135168 expected but may also lead to memcg_stat_test 4 TINFO: Test unevictable with mlock memcg_stat_test 4 TINFO: Running memcg_process --mmap-lock2 -s 135168 memcg_stat_test 4 TINFO: Warming up pid: 4271 memcg_stat_test 4 TINFO: Process is still here after warm up: 4271 memcg_stat_test 4 TFAIL: unevictable is 122880, 135168 expected or both. A wee bit flaky. follow_page_pte() used to have an lru_add_drain() per each page mlocked, and the test came to rely on accurate stats. The pagevec to be drained is different now, but still covered by lru_add_drain(); and, never mind the test, I believe it's in everyone's interest that a bulk faulting interface like populate_vma_page_range() or faultin_vma_page_range() should drain its local pagevecs at the end, to save others sometimes needing the much more expensive lru_add_drain_all(). This does not absolutely guarantee exact stats - the mlocking task can be migrated between CPUs as it proceeds - but it's good enough and the tests pass. Link: https://lkml.kernel.org/r/47f6d39c-a075-50cb-1cfb-26dd957a48af@google.com Fixes: b67bf49ce7aa ("mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE") Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Mike Galbraith <efault@gmx.de> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-04-02 02:28:27 +08:00
long ret;
mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables I. Background: Sparse Memory Mappings When we manage sparse memory mappings dynamically in user space - also sometimes involving MAP_NORESERVE - we want to dynamically populate/ discard memory inside such a sparse memory region. Example users are hypervisors (especially implementing memory ballooning or similar technologies like virtio-mem) and memory allocators. In addition, we want to fail in a nice way (instead of generating SIGBUS) if populating does not succeed because we are out of backend memory (which can happen easily with file-based mappings, especially tmpfs and hugetlbfs). While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for reliably discarding memory for most mapping types, there is no generic approach to populate page tables and preallocate memory. Although mmap() supports MAP_POPULATE, it is not applicable to the concept of sparse memory mappings, where we want to populate/discard dynamically and avoid expensive/problematic remappings. In addition, we never actually report errors during the final populate phase - it is best-effort only. fallocate() can be used to preallocate file-based memory and fail in a safe way. However, it cannot really be used for any private mappings on anonymous files via memfd due to COW semantics. In addition, fallocate() does not actually populate page tables, so we still always get pagefaults on first access - which is sometimes undesired (i.e., real-time workloads) and requires real prefaulting of page tables, not just a preallocation of backend storage. There might be interesting use cases for sparse memory regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy as it does not prefault page tables. II. On preallcoation/prefaulting from user space Because we don't have a proper interface, what applications (like QEMU and databases) end up doing is touching (i.e., reading+writing one byte to not overwrite existing data) all individual pages. However, that approach 1) Can result in wear on storage backing, because we end up reading/writing each page; this is especially a problem for dax/pmem. 2) Can result in mmap_sem contention when prefaulting via multiple threads. 3) Requires expensive signal handling, especially to catch SIGBUS in case of hugetlbfs/shmem/file-backed memory. For example, this is problematic in hypervisors like QEMU where SIGBUS handlers might already be used by other subsystems concurrently to e.g, handle hardware errors. "Simply" doing preallocation concurrently from other thread is not that easy. III. On MADV_WILLNEED Extending MADV_WILLNEED is not an option because 1. It would change the semantics: "Expect access in the near future." and "might be a good idea to read some pages" vs. "Definitely populate/ preallocate all memory and definitely fail on errors.". 2. Existing users (like virtio-balloon in QEMU when deflating the balloon) don't want populate/prealloc semantics. They treat this rather as a hint to give a little performance boost without too much overhead - and don't expect that a lot of memory might get consumed or a lot of time might be spent. IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by MAP_POPULATE, with the following semantics: 1. MADV_POPULATE_READ can be used to prefault page tables just like manually reading each individual page. This will not break any COW mappings. The shared zero page might get mapped and no backend storage might get preallocated -- allocation might be deferred to write-fault time. Especially shared file mappings require an explicit fallocate() upfront to actually preallocate backend memory (blocks in the file system) in case the file might have holes. 2. If MADV_POPULATE_READ succeeds, all page tables have been populated (prefaulted) readable once. 3. MADV_POPULATE_WRITE can be used to preallocate backend memory and prefault page tables just like manually writing (or reading+writing) each individual page. This will break any COW mappings -- e.g., the shared zeropage is never populated. 4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated (prefaulted) writable once. 5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special mappings marked with VM_PFNMAP and VM_IO. Also, proper access permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such mapping is encountered, madvise() fails with -EINVAL. 6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables might have been populated. 7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON when encountering a HW poisoned page in the range. 8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot protect from the OOM (Out Of Memory) handler killing the process. While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e., preallocate memory and prefault page tables for VMs), one issue is that whenever we prefault pages writable, the pages have to be marked dirty, because the CPU could dirty them any time. while not a real problem for hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each page will be marked dirty and has to be written back later when evicting. MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole mapping from backend storage without marking it dirty, such that eviction won't have to write it back. As discussed above, shared file mappings might require an explciit fallocate() upfront to achieve preallcoation+prepopulation. Although sparse memory mappings are the primary use case, this will also be useful for other preallocate/prefault use cases where MAP_POPULATE is not desired or the semantics of MAP_POPULATE are not sufficient: as one example, QEMU users can trigger preallocation/prefaulting of guest RAM after the mapping was created -- and don't want errors to be silently suppressed. Looking at the history, MADV_POPULATE was already proposed in 2013 [1], however, the main motivation back than was performance improvements -- which should also still be the case. V. Single-threaded performance comparison I did a short experiment, prefaulting page tables on completely *empty mappings/files* and repeated the experiment 10 times. The results correspond to the shortest execution time. In general, the performance benefit for huge pages is negligible with small mappings. V.1: Private mappings POPULATE_READ and POPULATE_WRITE is fastest. Note that Reading/POPULATE_READ will populate the shared zeropage where applicable -- which result in short population times. The fastest way to allocate backend storage (here: swap or huge pages) and prefault page tables is POPULATE_WRITE. V.2: Shared mappings fallocate() is fastest, however, doesn't prefault page tables. POPULATE_WRITE is faster than simple writes and read/writes. POPULATE_READ is faster than simple reads. Without a fd, the fastest way to allocate backend storage and prefault page tables is POPULATE_WRITE. With an fd, the fastest way is usually FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one exception are actual files: FALLOCATE+Read is slightly faster than FALLOCATE+POPULATE_READ. The fastest way to allocate backend storage prefault page tables is FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then, FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as dirty. v.3: Detailed results ================================================== 2 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 0.119 ms Anon 4 KiB : Write : 0.222 ms Anon 4 KiB : Read/Write : 0.380 ms Anon 4 KiB : POPULATE_READ : 0.060 ms Anon 4 KiB : POPULATE_WRITE : 0.158 ms Memfd 4 KiB : Read : 0.034 ms Memfd 4 KiB : Write : 0.310 ms Memfd 4 KiB : Read/Write : 0.362 ms Memfd 4 KiB : POPULATE_READ : 0.039 ms Memfd 4 KiB : POPULATE_WRITE : 0.229 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.033 ms tmpfs : Write : 0.313 ms tmpfs : Read/Write : 0.406 ms tmpfs : POPULATE_READ : 0.039 ms tmpfs : POPULATE_WRITE : 0.285 ms file : Read : 0.033 ms file : Write : 0.351 ms file : Read/Write : 0.408 ms file : POPULATE_READ : 0.039 ms file : POPULATE_WRITE : 0.290 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 237.940 ms Anon 4 KiB : Write : 708.409 ms Anon 4 KiB : Read/Write : 1054.041 ms Anon 4 KiB : POPULATE_READ : 124.310 ms Anon 4 KiB : POPULATE_WRITE : 572.582 ms Memfd 4 KiB : Read : 136.928 ms Memfd 4 KiB : Write : 963.898 ms Memfd 4 KiB : Read/Write : 1106.561 ms Memfd 4 KiB : POPULATE_READ : 78.450 ms Memfd 4 KiB : POPULATE_WRITE : 805.881 ms Memfd 2 MiB : Read : 357.116 ms Memfd 2 MiB : Write : 357.210 ms Memfd 2 MiB : Read/Write : 357.606 ms Memfd 2 MiB : POPULATE_READ : 356.094 ms Memfd 2 MiB : POPULATE_WRITE : 356.937 ms tmpfs : Read : 137.536 ms tmpfs : Write : 954.362 ms tmpfs : Read/Write : 1105.954 ms tmpfs : POPULATE_READ : 80.289 ms tmpfs : POPULATE_WRITE : 822.826 ms file : Read : 137.874 ms file : Write : 987.025 ms file : Read/Write : 1107.439 ms file : POPULATE_READ : 80.413 ms file : POPULATE_WRITE : 857.622 ms hugetlbfs : Read : 355.607 ms hugetlbfs : Write : 355.729 ms hugetlbfs : Read/Write : 356.127 ms hugetlbfs : POPULATE_READ : 354.585 ms hugetlbfs : POPULATE_WRITE : 355.138 ms ************************************************** 2 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 0.394 ms Anon 4 KiB : Write : 0.348 ms Anon 4 KiB : Read/Write : 0.400 ms Anon 4 KiB : POPULATE_READ : 0.326 ms Anon 4 KiB : POPULATE_WRITE : 0.273 ms Anon 2 MiB : Read : 0.030 ms Anon 2 MiB : Write : 0.030 ms Anon 2 MiB : Read/Write : 0.030 ms Anon 2 MiB : POPULATE_READ : 0.030 ms Anon 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 4 KiB : Read : 0.412 ms Memfd 4 KiB : Write : 0.372 ms Memfd 4 KiB : Read/Write : 0.419 ms Memfd 4 KiB : POPULATE_READ : 0.343 ms Memfd 4 KiB : POPULATE_WRITE : 0.288 ms Memfd 4 KiB : FALLOCATE : 0.137 ms Memfd 4 KiB : FALLOCATE+Read : 0.446 ms Memfd 4 KiB : FALLOCATE+Write : 0.330 ms Memfd 4 KiB : FALLOCATE+Read/Write : 0.454 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 0.379 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 0.268 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 2 MiB : FALLOCATE : 0.030 ms Memfd 2 MiB : FALLOCATE+Read : 0.031 ms Memfd 2 MiB : FALLOCATE+Write : 0.031 ms Memfd 2 MiB : FALLOCATE+Read/Write : 0.031 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 0.030 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.416 ms tmpfs : Write : 0.369 ms tmpfs : Read/Write : 0.425 ms tmpfs : POPULATE_READ : 0.346 ms tmpfs : POPULATE_WRITE : 0.295 ms tmpfs : FALLOCATE : 0.139 ms tmpfs : FALLOCATE+Read : 0.447 ms tmpfs : FALLOCATE+Write : 0.333 ms tmpfs : FALLOCATE+Read/Write : 0.454 ms tmpfs : FALLOCATE+POPULATE_READ : 0.380 ms tmpfs : FALLOCATE+POPULATE_WRITE : 0.272 ms file : Read : 0.191 ms file : Write : 0.511 ms file : Read/Write : 0.524 ms file : POPULATE_READ : 0.196 ms file : POPULATE_WRITE : 0.434 ms file : FALLOCATE : 0.004 ms file : FALLOCATE+Read : 0.197 ms file : FALLOCATE+Write : 0.554 ms file : FALLOCATE+Read/Write : 0.480 ms file : FALLOCATE+POPULATE_READ : 0.201 ms file : FALLOCATE+POPULATE_WRITE : 0.381 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms hugetlbfs : FALLOCATE : 0.030 ms hugetlbfs : FALLOCATE+Read : 0.031 ms hugetlbfs : FALLOCATE+Write : 0.031 ms hugetlbfs : FALLOCATE+Read/Write : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_READ : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 1053.090 ms Anon 4 KiB : Write : 913.642 ms Anon 4 KiB : Read/Write : 1060.350 ms Anon 4 KiB : POPULATE_READ : 893.691 ms Anon 4 KiB : POPULATE_WRITE : 782.885 ms Anon 2 MiB : Read : 358.553 ms Anon 2 MiB : Write : 358.419 ms Anon 2 MiB : Read/Write : 357.992 ms Anon 2 MiB : POPULATE_READ : 357.533 ms Anon 2 MiB : POPULATE_WRITE : 357.808 ms Memfd 4 KiB : Read : 1078.144 ms Memfd 4 KiB : Write : 942.036 ms Memfd 4 KiB : Read/Write : 1100.391 ms Memfd 4 KiB : POPULATE_READ : 925.829 ms Memfd 4 KiB : POPULATE_WRITE : 804.394 ms Memfd 4 KiB : FALLOCATE : 304.632 ms Memfd 4 KiB : FALLOCATE+Read : 1163.359 ms Memfd 4 KiB : FALLOCATE+Write : 933.186 ms Memfd 4 KiB : FALLOCATE+Read/Write : 1187.304 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 1013.660 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 794.560 ms Memfd 2 MiB : Read : 358.131 ms Memfd 2 MiB : Write : 358.099 ms Memfd 2 MiB : Read/Write : 358.250 ms Memfd 2 MiB : POPULATE_READ : 357.563 ms Memfd 2 MiB : POPULATE_WRITE : 357.334 ms Memfd 2 MiB : FALLOCATE : 356.735 ms Memfd 2 MiB : FALLOCATE+Read : 358.152 ms Memfd 2 MiB : FALLOCATE+Write : 358.331 ms Memfd 2 MiB : FALLOCATE+Read/Write : 358.018 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 357.286 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 357.523 ms tmpfs : Read : 1087.265 ms tmpfs : Write : 950.840 ms tmpfs : Read/Write : 1107.567 ms tmpfs : POPULATE_READ : 922.605 ms tmpfs : POPULATE_WRITE : 810.094 ms tmpfs : FALLOCATE : 306.320 ms tmpfs : FALLOCATE+Read : 1169.796 ms tmpfs : FALLOCATE+Write : 933.730 ms tmpfs : FALLOCATE+Read/Write : 1191.610 ms tmpfs : FALLOCATE+POPULATE_READ : 1020.474 ms tmpfs : FALLOCATE+POPULATE_WRITE : 798.945 ms file : Read : 654.101 ms file : Write : 1259.142 ms file : Read/Write : 1289.509 ms file : POPULATE_READ : 661.642 ms file : POPULATE_WRITE : 1106.816 ms file : FALLOCATE : 1.864 ms file : FALLOCATE+Read : 656.328 ms file : FALLOCATE+Write : 1153.300 ms file : FALLOCATE+Read/Write : 1180.613 ms file : FALLOCATE+POPULATE_READ : 668.347 ms file : FALLOCATE+POPULATE_WRITE : 996.143 ms hugetlbfs : Read : 357.245 ms hugetlbfs : Write : 357.413 ms hugetlbfs : Read/Write : 357.120 ms hugetlbfs : POPULATE_READ : 356.321 ms hugetlbfs : POPULATE_WRITE : 356.693 ms hugetlbfs : FALLOCATE : 355.927 ms hugetlbfs : FALLOCATE+Read : 357.074 ms hugetlbfs : FALLOCATE+Write : 357.120 ms hugetlbfs : FALLOCATE+Read/Write : 356.983 ms hugetlbfs : FALLOCATE+POPULATE_READ : 356.413 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 356.266 ms ************************************************** [1] https://lkml.org/lkml/2013/6/27/698 [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 09:52:28 +08:00
VM_BUG_ON(!PAGE_ALIGNED(start));
VM_BUG_ON(!PAGE_ALIGNED(end));
VM_BUG_ON_VMA(start < vma->vm_start, vma);
VM_BUG_ON_VMA(end > vma->vm_end, vma);
mmap_assert_locked(mm);
/*
* FOLL_TOUCH: Mark page accessed and thereby young; will also mark
* the page dirty with FOLL_WRITE -- which doesn't make a
* difference with !FOLL_FORCE, because the page is writable
* in the page table.
* FOLL_HWPOISON: Return -EHWPOISON instead of -EFAULT when we hit
* a poisoned page.
* !FOLL_FORCE: Require proper access permissions.
*/
gup_flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_UNLOCKABLE;
mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables I. Background: Sparse Memory Mappings When we manage sparse memory mappings dynamically in user space - also sometimes involving MAP_NORESERVE - we want to dynamically populate/ discard memory inside such a sparse memory region. Example users are hypervisors (especially implementing memory ballooning or similar technologies like virtio-mem) and memory allocators. In addition, we want to fail in a nice way (instead of generating SIGBUS) if populating does not succeed because we are out of backend memory (which can happen easily with file-based mappings, especially tmpfs and hugetlbfs). While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for reliably discarding memory for most mapping types, there is no generic approach to populate page tables and preallocate memory. Although mmap() supports MAP_POPULATE, it is not applicable to the concept of sparse memory mappings, where we want to populate/discard dynamically and avoid expensive/problematic remappings. In addition, we never actually report errors during the final populate phase - it is best-effort only. fallocate() can be used to preallocate file-based memory and fail in a safe way. However, it cannot really be used for any private mappings on anonymous files via memfd due to COW semantics. In addition, fallocate() does not actually populate page tables, so we still always get pagefaults on first access - which is sometimes undesired (i.e., real-time workloads) and requires real prefaulting of page tables, not just a preallocation of backend storage. There might be interesting use cases for sparse memory regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy as it does not prefault page tables. II. On preallcoation/prefaulting from user space Because we don't have a proper interface, what applications (like QEMU and databases) end up doing is touching (i.e., reading+writing one byte to not overwrite existing data) all individual pages. However, that approach 1) Can result in wear on storage backing, because we end up reading/writing each page; this is especially a problem for dax/pmem. 2) Can result in mmap_sem contention when prefaulting via multiple threads. 3) Requires expensive signal handling, especially to catch SIGBUS in case of hugetlbfs/shmem/file-backed memory. For example, this is problematic in hypervisors like QEMU where SIGBUS handlers might already be used by other subsystems concurrently to e.g, handle hardware errors. "Simply" doing preallocation concurrently from other thread is not that easy. III. On MADV_WILLNEED Extending MADV_WILLNEED is not an option because 1. It would change the semantics: "Expect access in the near future." and "might be a good idea to read some pages" vs. "Definitely populate/ preallocate all memory and definitely fail on errors.". 2. Existing users (like virtio-balloon in QEMU when deflating the balloon) don't want populate/prealloc semantics. They treat this rather as a hint to give a little performance boost without too much overhead - and don't expect that a lot of memory might get consumed or a lot of time might be spent. IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by MAP_POPULATE, with the following semantics: 1. MADV_POPULATE_READ can be used to prefault page tables just like manually reading each individual page. This will not break any COW mappings. The shared zero page might get mapped and no backend storage might get preallocated -- allocation might be deferred to write-fault time. Especially shared file mappings require an explicit fallocate() upfront to actually preallocate backend memory (blocks in the file system) in case the file might have holes. 2. If MADV_POPULATE_READ succeeds, all page tables have been populated (prefaulted) readable once. 3. MADV_POPULATE_WRITE can be used to preallocate backend memory and prefault page tables just like manually writing (or reading+writing) each individual page. This will break any COW mappings -- e.g., the shared zeropage is never populated. 4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated (prefaulted) writable once. 5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special mappings marked with VM_PFNMAP and VM_IO. Also, proper access permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such mapping is encountered, madvise() fails with -EINVAL. 6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables might have been populated. 7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON when encountering a HW poisoned page in the range. 8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot protect from the OOM (Out Of Memory) handler killing the process. While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e., preallocate memory and prefault page tables for VMs), one issue is that whenever we prefault pages writable, the pages have to be marked dirty, because the CPU could dirty them any time. while not a real problem for hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each page will be marked dirty and has to be written back later when evicting. MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole mapping from backend storage without marking it dirty, such that eviction won't have to write it back. As discussed above, shared file mappings might require an explciit fallocate() upfront to achieve preallcoation+prepopulation. Although sparse memory mappings are the primary use case, this will also be useful for other preallocate/prefault use cases where MAP_POPULATE is not desired or the semantics of MAP_POPULATE are not sufficient: as one example, QEMU users can trigger preallocation/prefaulting of guest RAM after the mapping was created -- and don't want errors to be silently suppressed. Looking at the history, MADV_POPULATE was already proposed in 2013 [1], however, the main motivation back than was performance improvements -- which should also still be the case. V. Single-threaded performance comparison I did a short experiment, prefaulting page tables on completely *empty mappings/files* and repeated the experiment 10 times. The results correspond to the shortest execution time. In general, the performance benefit for huge pages is negligible with small mappings. V.1: Private mappings POPULATE_READ and POPULATE_WRITE is fastest. Note that Reading/POPULATE_READ will populate the shared zeropage where applicable -- which result in short population times. The fastest way to allocate backend storage (here: swap or huge pages) and prefault page tables is POPULATE_WRITE. V.2: Shared mappings fallocate() is fastest, however, doesn't prefault page tables. POPULATE_WRITE is faster than simple writes and read/writes. POPULATE_READ is faster than simple reads. Without a fd, the fastest way to allocate backend storage and prefault page tables is POPULATE_WRITE. With an fd, the fastest way is usually FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one exception are actual files: FALLOCATE+Read is slightly faster than FALLOCATE+POPULATE_READ. The fastest way to allocate backend storage prefault page tables is FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then, FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as dirty. v.3: Detailed results ================================================== 2 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 0.119 ms Anon 4 KiB : Write : 0.222 ms Anon 4 KiB : Read/Write : 0.380 ms Anon 4 KiB : POPULATE_READ : 0.060 ms Anon 4 KiB : POPULATE_WRITE : 0.158 ms Memfd 4 KiB : Read : 0.034 ms Memfd 4 KiB : Write : 0.310 ms Memfd 4 KiB : Read/Write : 0.362 ms Memfd 4 KiB : POPULATE_READ : 0.039 ms Memfd 4 KiB : POPULATE_WRITE : 0.229 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.033 ms tmpfs : Write : 0.313 ms tmpfs : Read/Write : 0.406 ms tmpfs : POPULATE_READ : 0.039 ms tmpfs : POPULATE_WRITE : 0.285 ms file : Read : 0.033 ms file : Write : 0.351 ms file : Read/Write : 0.408 ms file : POPULATE_READ : 0.039 ms file : POPULATE_WRITE : 0.290 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 237.940 ms Anon 4 KiB : Write : 708.409 ms Anon 4 KiB : Read/Write : 1054.041 ms Anon 4 KiB : POPULATE_READ : 124.310 ms Anon 4 KiB : POPULATE_WRITE : 572.582 ms Memfd 4 KiB : Read : 136.928 ms Memfd 4 KiB : Write : 963.898 ms Memfd 4 KiB : Read/Write : 1106.561 ms Memfd 4 KiB : POPULATE_READ : 78.450 ms Memfd 4 KiB : POPULATE_WRITE : 805.881 ms Memfd 2 MiB : Read : 357.116 ms Memfd 2 MiB : Write : 357.210 ms Memfd 2 MiB : Read/Write : 357.606 ms Memfd 2 MiB : POPULATE_READ : 356.094 ms Memfd 2 MiB : POPULATE_WRITE : 356.937 ms tmpfs : Read : 137.536 ms tmpfs : Write : 954.362 ms tmpfs : Read/Write : 1105.954 ms tmpfs : POPULATE_READ : 80.289 ms tmpfs : POPULATE_WRITE : 822.826 ms file : Read : 137.874 ms file : Write : 987.025 ms file : Read/Write : 1107.439 ms file : POPULATE_READ : 80.413 ms file : POPULATE_WRITE : 857.622 ms hugetlbfs : Read : 355.607 ms hugetlbfs : Write : 355.729 ms hugetlbfs : Read/Write : 356.127 ms hugetlbfs : POPULATE_READ : 354.585 ms hugetlbfs : POPULATE_WRITE : 355.138 ms ************************************************** 2 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 0.394 ms Anon 4 KiB : Write : 0.348 ms Anon 4 KiB : Read/Write : 0.400 ms Anon 4 KiB : POPULATE_READ : 0.326 ms Anon 4 KiB : POPULATE_WRITE : 0.273 ms Anon 2 MiB : Read : 0.030 ms Anon 2 MiB : Write : 0.030 ms Anon 2 MiB : Read/Write : 0.030 ms Anon 2 MiB : POPULATE_READ : 0.030 ms Anon 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 4 KiB : Read : 0.412 ms Memfd 4 KiB : Write : 0.372 ms Memfd 4 KiB : Read/Write : 0.419 ms Memfd 4 KiB : POPULATE_READ : 0.343 ms Memfd 4 KiB : POPULATE_WRITE : 0.288 ms Memfd 4 KiB : FALLOCATE : 0.137 ms Memfd 4 KiB : FALLOCATE+Read : 0.446 ms Memfd 4 KiB : FALLOCATE+Write : 0.330 ms Memfd 4 KiB : FALLOCATE+Read/Write : 0.454 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 0.379 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 0.268 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 2 MiB : FALLOCATE : 0.030 ms Memfd 2 MiB : FALLOCATE+Read : 0.031 ms Memfd 2 MiB : FALLOCATE+Write : 0.031 ms Memfd 2 MiB : FALLOCATE+Read/Write : 0.031 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 0.030 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.416 ms tmpfs : Write : 0.369 ms tmpfs : Read/Write : 0.425 ms tmpfs : POPULATE_READ : 0.346 ms tmpfs : POPULATE_WRITE : 0.295 ms tmpfs : FALLOCATE : 0.139 ms tmpfs : FALLOCATE+Read : 0.447 ms tmpfs : FALLOCATE+Write : 0.333 ms tmpfs : FALLOCATE+Read/Write : 0.454 ms tmpfs : FALLOCATE+POPULATE_READ : 0.380 ms tmpfs : FALLOCATE+POPULATE_WRITE : 0.272 ms file : Read : 0.191 ms file : Write : 0.511 ms file : Read/Write : 0.524 ms file : POPULATE_READ : 0.196 ms file : POPULATE_WRITE : 0.434 ms file : FALLOCATE : 0.004 ms file : FALLOCATE+Read : 0.197 ms file : FALLOCATE+Write : 0.554 ms file : FALLOCATE+Read/Write : 0.480 ms file : FALLOCATE+POPULATE_READ : 0.201 ms file : FALLOCATE+POPULATE_WRITE : 0.381 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms hugetlbfs : FALLOCATE : 0.030 ms hugetlbfs : FALLOCATE+Read : 0.031 ms hugetlbfs : FALLOCATE+Write : 0.031 ms hugetlbfs : FALLOCATE+Read/Write : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_READ : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 1053.090 ms Anon 4 KiB : Write : 913.642 ms Anon 4 KiB : Read/Write : 1060.350 ms Anon 4 KiB : POPULATE_READ : 893.691 ms Anon 4 KiB : POPULATE_WRITE : 782.885 ms Anon 2 MiB : Read : 358.553 ms Anon 2 MiB : Write : 358.419 ms Anon 2 MiB : Read/Write : 357.992 ms Anon 2 MiB : POPULATE_READ : 357.533 ms Anon 2 MiB : POPULATE_WRITE : 357.808 ms Memfd 4 KiB : Read : 1078.144 ms Memfd 4 KiB : Write : 942.036 ms Memfd 4 KiB : Read/Write : 1100.391 ms Memfd 4 KiB : POPULATE_READ : 925.829 ms Memfd 4 KiB : POPULATE_WRITE : 804.394 ms Memfd 4 KiB : FALLOCATE : 304.632 ms Memfd 4 KiB : FALLOCATE+Read : 1163.359 ms Memfd 4 KiB : FALLOCATE+Write : 933.186 ms Memfd 4 KiB : FALLOCATE+Read/Write : 1187.304 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 1013.660 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 794.560 ms Memfd 2 MiB : Read : 358.131 ms Memfd 2 MiB : Write : 358.099 ms Memfd 2 MiB : Read/Write : 358.250 ms Memfd 2 MiB : POPULATE_READ : 357.563 ms Memfd 2 MiB : POPULATE_WRITE : 357.334 ms Memfd 2 MiB : FALLOCATE : 356.735 ms Memfd 2 MiB : FALLOCATE+Read : 358.152 ms Memfd 2 MiB : FALLOCATE+Write : 358.331 ms Memfd 2 MiB : FALLOCATE+Read/Write : 358.018 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 357.286 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 357.523 ms tmpfs : Read : 1087.265 ms tmpfs : Write : 950.840 ms tmpfs : Read/Write : 1107.567 ms tmpfs : POPULATE_READ : 922.605 ms tmpfs : POPULATE_WRITE : 810.094 ms tmpfs : FALLOCATE : 306.320 ms tmpfs : FALLOCATE+Read : 1169.796 ms tmpfs : FALLOCATE+Write : 933.730 ms tmpfs : FALLOCATE+Read/Write : 1191.610 ms tmpfs : FALLOCATE+POPULATE_READ : 1020.474 ms tmpfs : FALLOCATE+POPULATE_WRITE : 798.945 ms file : Read : 654.101 ms file : Write : 1259.142 ms file : Read/Write : 1289.509 ms file : POPULATE_READ : 661.642 ms file : POPULATE_WRITE : 1106.816 ms file : FALLOCATE : 1.864 ms file : FALLOCATE+Read : 656.328 ms file : FALLOCATE+Write : 1153.300 ms file : FALLOCATE+Read/Write : 1180.613 ms file : FALLOCATE+POPULATE_READ : 668.347 ms file : FALLOCATE+POPULATE_WRITE : 996.143 ms hugetlbfs : Read : 357.245 ms hugetlbfs : Write : 357.413 ms hugetlbfs : Read/Write : 357.120 ms hugetlbfs : POPULATE_READ : 356.321 ms hugetlbfs : POPULATE_WRITE : 356.693 ms hugetlbfs : FALLOCATE : 355.927 ms hugetlbfs : FALLOCATE+Read : 357.074 ms hugetlbfs : FALLOCATE+Write : 357.120 ms hugetlbfs : FALLOCATE+Read/Write : 356.983 ms hugetlbfs : FALLOCATE+POPULATE_READ : 356.413 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 356.266 ms ************************************************** [1] https://lkml.org/lkml/2013/6/27/698 [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 09:52:28 +08:00
if (write)
gup_flags |= FOLL_WRITE;
/*
mm/madvise: report SIGBUS as -EFAULT for MADV_POPULATE_(READ|WRITE) Doing some extended tests and polishing the man page update for MADV_POPULATE_(READ|WRITE), I realized that we end up converting also SIGBUS (via -EFAULT) to -EINVAL, making it look like yet another madvise() user error. We want to report only problematic mappings and permission problems that the user could have know as -EINVAL. Let's not convert -EFAULT arising due to SIGBUS (or SIGSEGV) to -EINVAL, but instead indicate -EFAULT to user space. While we could also convert it to -ENOMEM, using -EFAULT looks more helpful when user space might want to troubleshoot what's going wrong: MADV_POPULATE_(READ|WRITE) is not part of an final Linux release and we can still adjust the behavior. Link: https://lkml.kernel.org/r/20210726154932.102880-1-david@redhat.com Fixes: 4ca9b3859dac ("mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables") Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-08-14 07:54:37 +08:00
* We want to report -EINVAL instead of -EFAULT for any permission
* problems or incompatible mappings.
mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables I. Background: Sparse Memory Mappings When we manage sparse memory mappings dynamically in user space - also sometimes involving MAP_NORESERVE - we want to dynamically populate/ discard memory inside such a sparse memory region. Example users are hypervisors (especially implementing memory ballooning or similar technologies like virtio-mem) and memory allocators. In addition, we want to fail in a nice way (instead of generating SIGBUS) if populating does not succeed because we are out of backend memory (which can happen easily with file-based mappings, especially tmpfs and hugetlbfs). While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for reliably discarding memory for most mapping types, there is no generic approach to populate page tables and preallocate memory. Although mmap() supports MAP_POPULATE, it is not applicable to the concept of sparse memory mappings, where we want to populate/discard dynamically and avoid expensive/problematic remappings. In addition, we never actually report errors during the final populate phase - it is best-effort only. fallocate() can be used to preallocate file-based memory and fail in a safe way. However, it cannot really be used for any private mappings on anonymous files via memfd due to COW semantics. In addition, fallocate() does not actually populate page tables, so we still always get pagefaults on first access - which is sometimes undesired (i.e., real-time workloads) and requires real prefaulting of page tables, not just a preallocation of backend storage. There might be interesting use cases for sparse memory regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy as it does not prefault page tables. II. On preallcoation/prefaulting from user space Because we don't have a proper interface, what applications (like QEMU and databases) end up doing is touching (i.e., reading+writing one byte to not overwrite existing data) all individual pages. However, that approach 1) Can result in wear on storage backing, because we end up reading/writing each page; this is especially a problem for dax/pmem. 2) Can result in mmap_sem contention when prefaulting via multiple threads. 3) Requires expensive signal handling, especially to catch SIGBUS in case of hugetlbfs/shmem/file-backed memory. For example, this is problematic in hypervisors like QEMU where SIGBUS handlers might already be used by other subsystems concurrently to e.g, handle hardware errors. "Simply" doing preallocation concurrently from other thread is not that easy. III. On MADV_WILLNEED Extending MADV_WILLNEED is not an option because 1. It would change the semantics: "Expect access in the near future." and "might be a good idea to read some pages" vs. "Definitely populate/ preallocate all memory and definitely fail on errors.". 2. Existing users (like virtio-balloon in QEMU when deflating the balloon) don't want populate/prealloc semantics. They treat this rather as a hint to give a little performance boost without too much overhead - and don't expect that a lot of memory might get consumed or a lot of time might be spent. IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by MAP_POPULATE, with the following semantics: 1. MADV_POPULATE_READ can be used to prefault page tables just like manually reading each individual page. This will not break any COW mappings. The shared zero page might get mapped and no backend storage might get preallocated -- allocation might be deferred to write-fault time. Especially shared file mappings require an explicit fallocate() upfront to actually preallocate backend memory (blocks in the file system) in case the file might have holes. 2. If MADV_POPULATE_READ succeeds, all page tables have been populated (prefaulted) readable once. 3. MADV_POPULATE_WRITE can be used to preallocate backend memory and prefault page tables just like manually writing (or reading+writing) each individual page. This will break any COW mappings -- e.g., the shared zeropage is never populated. 4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated (prefaulted) writable once. 5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special mappings marked with VM_PFNMAP and VM_IO. Also, proper access permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such mapping is encountered, madvise() fails with -EINVAL. 6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables might have been populated. 7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON when encountering a HW poisoned page in the range. 8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot protect from the OOM (Out Of Memory) handler killing the process. While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e., preallocate memory and prefault page tables for VMs), one issue is that whenever we prefault pages writable, the pages have to be marked dirty, because the CPU could dirty them any time. while not a real problem for hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each page will be marked dirty and has to be written back later when evicting. MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole mapping from backend storage without marking it dirty, such that eviction won't have to write it back. As discussed above, shared file mappings might require an explciit fallocate() upfront to achieve preallcoation+prepopulation. Although sparse memory mappings are the primary use case, this will also be useful for other preallocate/prefault use cases where MAP_POPULATE is not desired or the semantics of MAP_POPULATE are not sufficient: as one example, QEMU users can trigger preallocation/prefaulting of guest RAM after the mapping was created -- and don't want errors to be silently suppressed. Looking at the history, MADV_POPULATE was already proposed in 2013 [1], however, the main motivation back than was performance improvements -- which should also still be the case. V. Single-threaded performance comparison I did a short experiment, prefaulting page tables on completely *empty mappings/files* and repeated the experiment 10 times. The results correspond to the shortest execution time. In general, the performance benefit for huge pages is negligible with small mappings. V.1: Private mappings POPULATE_READ and POPULATE_WRITE is fastest. Note that Reading/POPULATE_READ will populate the shared zeropage where applicable -- which result in short population times. The fastest way to allocate backend storage (here: swap or huge pages) and prefault page tables is POPULATE_WRITE. V.2: Shared mappings fallocate() is fastest, however, doesn't prefault page tables. POPULATE_WRITE is faster than simple writes and read/writes. POPULATE_READ is faster than simple reads. Without a fd, the fastest way to allocate backend storage and prefault page tables is POPULATE_WRITE. With an fd, the fastest way is usually FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one exception are actual files: FALLOCATE+Read is slightly faster than FALLOCATE+POPULATE_READ. The fastest way to allocate backend storage prefault page tables is FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then, FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as dirty. v.3: Detailed results ================================================== 2 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 0.119 ms Anon 4 KiB : Write : 0.222 ms Anon 4 KiB : Read/Write : 0.380 ms Anon 4 KiB : POPULATE_READ : 0.060 ms Anon 4 KiB : POPULATE_WRITE : 0.158 ms Memfd 4 KiB : Read : 0.034 ms Memfd 4 KiB : Write : 0.310 ms Memfd 4 KiB : Read/Write : 0.362 ms Memfd 4 KiB : POPULATE_READ : 0.039 ms Memfd 4 KiB : POPULATE_WRITE : 0.229 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.033 ms tmpfs : Write : 0.313 ms tmpfs : Read/Write : 0.406 ms tmpfs : POPULATE_READ : 0.039 ms tmpfs : POPULATE_WRITE : 0.285 ms file : Read : 0.033 ms file : Write : 0.351 ms file : Read/Write : 0.408 ms file : POPULATE_READ : 0.039 ms file : POPULATE_WRITE : 0.290 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 237.940 ms Anon 4 KiB : Write : 708.409 ms Anon 4 KiB : Read/Write : 1054.041 ms Anon 4 KiB : POPULATE_READ : 124.310 ms Anon 4 KiB : POPULATE_WRITE : 572.582 ms Memfd 4 KiB : Read : 136.928 ms Memfd 4 KiB : Write : 963.898 ms Memfd 4 KiB : Read/Write : 1106.561 ms Memfd 4 KiB : POPULATE_READ : 78.450 ms Memfd 4 KiB : POPULATE_WRITE : 805.881 ms Memfd 2 MiB : Read : 357.116 ms Memfd 2 MiB : Write : 357.210 ms Memfd 2 MiB : Read/Write : 357.606 ms Memfd 2 MiB : POPULATE_READ : 356.094 ms Memfd 2 MiB : POPULATE_WRITE : 356.937 ms tmpfs : Read : 137.536 ms tmpfs : Write : 954.362 ms tmpfs : Read/Write : 1105.954 ms tmpfs : POPULATE_READ : 80.289 ms tmpfs : POPULATE_WRITE : 822.826 ms file : Read : 137.874 ms file : Write : 987.025 ms file : Read/Write : 1107.439 ms file : POPULATE_READ : 80.413 ms file : POPULATE_WRITE : 857.622 ms hugetlbfs : Read : 355.607 ms hugetlbfs : Write : 355.729 ms hugetlbfs : Read/Write : 356.127 ms hugetlbfs : POPULATE_READ : 354.585 ms hugetlbfs : POPULATE_WRITE : 355.138 ms ************************************************** 2 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 0.394 ms Anon 4 KiB : Write : 0.348 ms Anon 4 KiB : Read/Write : 0.400 ms Anon 4 KiB : POPULATE_READ : 0.326 ms Anon 4 KiB : POPULATE_WRITE : 0.273 ms Anon 2 MiB : Read : 0.030 ms Anon 2 MiB : Write : 0.030 ms Anon 2 MiB : Read/Write : 0.030 ms Anon 2 MiB : POPULATE_READ : 0.030 ms Anon 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 4 KiB : Read : 0.412 ms Memfd 4 KiB : Write : 0.372 ms Memfd 4 KiB : Read/Write : 0.419 ms Memfd 4 KiB : POPULATE_READ : 0.343 ms Memfd 4 KiB : POPULATE_WRITE : 0.288 ms Memfd 4 KiB : FALLOCATE : 0.137 ms Memfd 4 KiB : FALLOCATE+Read : 0.446 ms Memfd 4 KiB : FALLOCATE+Write : 0.330 ms Memfd 4 KiB : FALLOCATE+Read/Write : 0.454 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 0.379 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 0.268 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 2 MiB : FALLOCATE : 0.030 ms Memfd 2 MiB : FALLOCATE+Read : 0.031 ms Memfd 2 MiB : FALLOCATE+Write : 0.031 ms Memfd 2 MiB : FALLOCATE+Read/Write : 0.031 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 0.030 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.416 ms tmpfs : Write : 0.369 ms tmpfs : Read/Write : 0.425 ms tmpfs : POPULATE_READ : 0.346 ms tmpfs : POPULATE_WRITE : 0.295 ms tmpfs : FALLOCATE : 0.139 ms tmpfs : FALLOCATE+Read : 0.447 ms tmpfs : FALLOCATE+Write : 0.333 ms tmpfs : FALLOCATE+Read/Write : 0.454 ms tmpfs : FALLOCATE+POPULATE_READ : 0.380 ms tmpfs : FALLOCATE+POPULATE_WRITE : 0.272 ms file : Read : 0.191 ms file : Write : 0.511 ms file : Read/Write : 0.524 ms file : POPULATE_READ : 0.196 ms file : POPULATE_WRITE : 0.434 ms file : FALLOCATE : 0.004 ms file : FALLOCATE+Read : 0.197 ms file : FALLOCATE+Write : 0.554 ms file : FALLOCATE+Read/Write : 0.480 ms file : FALLOCATE+POPULATE_READ : 0.201 ms file : FALLOCATE+POPULATE_WRITE : 0.381 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms hugetlbfs : FALLOCATE : 0.030 ms hugetlbfs : FALLOCATE+Read : 0.031 ms hugetlbfs : FALLOCATE+Write : 0.031 ms hugetlbfs : FALLOCATE+Read/Write : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_READ : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 1053.090 ms Anon 4 KiB : Write : 913.642 ms Anon 4 KiB : Read/Write : 1060.350 ms Anon 4 KiB : POPULATE_READ : 893.691 ms Anon 4 KiB : POPULATE_WRITE : 782.885 ms Anon 2 MiB : Read : 358.553 ms Anon 2 MiB : Write : 358.419 ms Anon 2 MiB : Read/Write : 357.992 ms Anon 2 MiB : POPULATE_READ : 357.533 ms Anon 2 MiB : POPULATE_WRITE : 357.808 ms Memfd 4 KiB : Read : 1078.144 ms Memfd 4 KiB : Write : 942.036 ms Memfd 4 KiB : Read/Write : 1100.391 ms Memfd 4 KiB : POPULATE_READ : 925.829 ms Memfd 4 KiB : POPULATE_WRITE : 804.394 ms Memfd 4 KiB : FALLOCATE : 304.632 ms Memfd 4 KiB : FALLOCATE+Read : 1163.359 ms Memfd 4 KiB : FALLOCATE+Write : 933.186 ms Memfd 4 KiB : FALLOCATE+Read/Write : 1187.304 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 1013.660 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 794.560 ms Memfd 2 MiB : Read : 358.131 ms Memfd 2 MiB : Write : 358.099 ms Memfd 2 MiB : Read/Write : 358.250 ms Memfd 2 MiB : POPULATE_READ : 357.563 ms Memfd 2 MiB : POPULATE_WRITE : 357.334 ms Memfd 2 MiB : FALLOCATE : 356.735 ms Memfd 2 MiB : FALLOCATE+Read : 358.152 ms Memfd 2 MiB : FALLOCATE+Write : 358.331 ms Memfd 2 MiB : FALLOCATE+Read/Write : 358.018 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 357.286 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 357.523 ms tmpfs : Read : 1087.265 ms tmpfs : Write : 950.840 ms tmpfs : Read/Write : 1107.567 ms tmpfs : POPULATE_READ : 922.605 ms tmpfs : POPULATE_WRITE : 810.094 ms tmpfs : FALLOCATE : 306.320 ms tmpfs : FALLOCATE+Read : 1169.796 ms tmpfs : FALLOCATE+Write : 933.730 ms tmpfs : FALLOCATE+Read/Write : 1191.610 ms tmpfs : FALLOCATE+POPULATE_READ : 1020.474 ms tmpfs : FALLOCATE+POPULATE_WRITE : 798.945 ms file : Read : 654.101 ms file : Write : 1259.142 ms file : Read/Write : 1289.509 ms file : POPULATE_READ : 661.642 ms file : POPULATE_WRITE : 1106.816 ms file : FALLOCATE : 1.864 ms file : FALLOCATE+Read : 656.328 ms file : FALLOCATE+Write : 1153.300 ms file : FALLOCATE+Read/Write : 1180.613 ms file : FALLOCATE+POPULATE_READ : 668.347 ms file : FALLOCATE+POPULATE_WRITE : 996.143 ms hugetlbfs : Read : 357.245 ms hugetlbfs : Write : 357.413 ms hugetlbfs : Read/Write : 357.120 ms hugetlbfs : POPULATE_READ : 356.321 ms hugetlbfs : POPULATE_WRITE : 356.693 ms hugetlbfs : FALLOCATE : 355.927 ms hugetlbfs : FALLOCATE+Read : 357.074 ms hugetlbfs : FALLOCATE+Write : 357.120 ms hugetlbfs : FALLOCATE+Read/Write : 356.983 ms hugetlbfs : FALLOCATE+POPULATE_READ : 356.413 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 356.266 ms ************************************************** [1] https://lkml.org/lkml/2013/6/27/698 [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 09:52:28 +08:00
*/
mm/madvise: report SIGBUS as -EFAULT for MADV_POPULATE_(READ|WRITE) Doing some extended tests and polishing the man page update for MADV_POPULATE_(READ|WRITE), I realized that we end up converting also SIGBUS (via -EFAULT) to -EINVAL, making it look like yet another madvise() user error. We want to report only problematic mappings and permission problems that the user could have know as -EINVAL. Let's not convert -EFAULT arising due to SIGBUS (or SIGSEGV) to -EINVAL, but instead indicate -EFAULT to user space. While we could also convert it to -ENOMEM, using -EFAULT looks more helpful when user space might want to troubleshoot what's going wrong: MADV_POPULATE_(READ|WRITE) is not part of an final Linux release and we can still adjust the behavior. Link: https://lkml.kernel.org/r/20210726154932.102880-1-david@redhat.com Fixes: 4ca9b3859dac ("mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables") Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-08-14 07:54:37 +08:00
if (check_vma_flags(vma, gup_flags))
return -EINVAL;
mm/munlock: add lru_add_drain() to fix memcg_stat_test Mike reports that LTP memcg_stat_test usually leads to memcg_stat_test 3 TINFO: Test unevictable with MAP_LOCKED memcg_stat_test 3 TINFO: Running memcg_process --mmap-lock1 -s 135168 memcg_stat_test 3 TINFO: Warming up pid: 3460 memcg_stat_test 3 TINFO: Process is still here after warm up: 3460 memcg_stat_test 3 TFAIL: unevictable is 122880, 135168 expected but may also lead to memcg_stat_test 4 TINFO: Test unevictable with mlock memcg_stat_test 4 TINFO: Running memcg_process --mmap-lock2 -s 135168 memcg_stat_test 4 TINFO: Warming up pid: 4271 memcg_stat_test 4 TINFO: Process is still here after warm up: 4271 memcg_stat_test 4 TFAIL: unevictable is 122880, 135168 expected or both. A wee bit flaky. follow_page_pte() used to have an lru_add_drain() per each page mlocked, and the test came to rely on accurate stats. The pagevec to be drained is different now, but still covered by lru_add_drain(); and, never mind the test, I believe it's in everyone's interest that a bulk faulting interface like populate_vma_page_range() or faultin_vma_page_range() should drain its local pagevecs at the end, to save others sometimes needing the much more expensive lru_add_drain_all(). This does not absolutely guarantee exact stats - the mlocking task can be migrated between CPUs as it proceeds - but it's good enough and the tests pass. Link: https://lkml.kernel.org/r/47f6d39c-a075-50cb-1cfb-26dd957a48af@google.com Fixes: b67bf49ce7aa ("mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE") Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Mike Galbraith <efault@gmx.de> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-04-02 02:28:27 +08:00
ret = __get_user_pages(mm, start, nr_pages, gup_flags,
mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables I. Background: Sparse Memory Mappings When we manage sparse memory mappings dynamically in user space - also sometimes involving MAP_NORESERVE - we want to dynamically populate/ discard memory inside such a sparse memory region. Example users are hypervisors (especially implementing memory ballooning or similar technologies like virtio-mem) and memory allocators. In addition, we want to fail in a nice way (instead of generating SIGBUS) if populating does not succeed because we are out of backend memory (which can happen easily with file-based mappings, especially tmpfs and hugetlbfs). While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for reliably discarding memory for most mapping types, there is no generic approach to populate page tables and preallocate memory. Although mmap() supports MAP_POPULATE, it is not applicable to the concept of sparse memory mappings, where we want to populate/discard dynamically and avoid expensive/problematic remappings. In addition, we never actually report errors during the final populate phase - it is best-effort only. fallocate() can be used to preallocate file-based memory and fail in a safe way. However, it cannot really be used for any private mappings on anonymous files via memfd due to COW semantics. In addition, fallocate() does not actually populate page tables, so we still always get pagefaults on first access - which is sometimes undesired (i.e., real-time workloads) and requires real prefaulting of page tables, not just a preallocation of backend storage. There might be interesting use cases for sparse memory regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy as it does not prefault page tables. II. On preallcoation/prefaulting from user space Because we don't have a proper interface, what applications (like QEMU and databases) end up doing is touching (i.e., reading+writing one byte to not overwrite existing data) all individual pages. However, that approach 1) Can result in wear on storage backing, because we end up reading/writing each page; this is especially a problem for dax/pmem. 2) Can result in mmap_sem contention when prefaulting via multiple threads. 3) Requires expensive signal handling, especially to catch SIGBUS in case of hugetlbfs/shmem/file-backed memory. For example, this is problematic in hypervisors like QEMU where SIGBUS handlers might already be used by other subsystems concurrently to e.g, handle hardware errors. "Simply" doing preallocation concurrently from other thread is not that easy. III. On MADV_WILLNEED Extending MADV_WILLNEED is not an option because 1. It would change the semantics: "Expect access in the near future." and "might be a good idea to read some pages" vs. "Definitely populate/ preallocate all memory and definitely fail on errors.". 2. Existing users (like virtio-balloon in QEMU when deflating the balloon) don't want populate/prealloc semantics. They treat this rather as a hint to give a little performance boost without too much overhead - and don't expect that a lot of memory might get consumed or a lot of time might be spent. IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by MAP_POPULATE, with the following semantics: 1. MADV_POPULATE_READ can be used to prefault page tables just like manually reading each individual page. This will not break any COW mappings. The shared zero page might get mapped and no backend storage might get preallocated -- allocation might be deferred to write-fault time. Especially shared file mappings require an explicit fallocate() upfront to actually preallocate backend memory (blocks in the file system) in case the file might have holes. 2. If MADV_POPULATE_READ succeeds, all page tables have been populated (prefaulted) readable once. 3. MADV_POPULATE_WRITE can be used to preallocate backend memory and prefault page tables just like manually writing (or reading+writing) each individual page. This will break any COW mappings -- e.g., the shared zeropage is never populated. 4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated (prefaulted) writable once. 5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special mappings marked with VM_PFNMAP and VM_IO. Also, proper access permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such mapping is encountered, madvise() fails with -EINVAL. 6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables might have been populated. 7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON when encountering a HW poisoned page in the range. 8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot protect from the OOM (Out Of Memory) handler killing the process. While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e., preallocate memory and prefault page tables for VMs), one issue is that whenever we prefault pages writable, the pages have to be marked dirty, because the CPU could dirty them any time. while not a real problem for hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each page will be marked dirty and has to be written back later when evicting. MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole mapping from backend storage without marking it dirty, such that eviction won't have to write it back. As discussed above, shared file mappings might require an explciit fallocate() upfront to achieve preallcoation+prepopulation. Although sparse memory mappings are the primary use case, this will also be useful for other preallocate/prefault use cases where MAP_POPULATE is not desired or the semantics of MAP_POPULATE are not sufficient: as one example, QEMU users can trigger preallocation/prefaulting of guest RAM after the mapping was created -- and don't want errors to be silently suppressed. Looking at the history, MADV_POPULATE was already proposed in 2013 [1], however, the main motivation back than was performance improvements -- which should also still be the case. V. Single-threaded performance comparison I did a short experiment, prefaulting page tables on completely *empty mappings/files* and repeated the experiment 10 times. The results correspond to the shortest execution time. In general, the performance benefit for huge pages is negligible with small mappings. V.1: Private mappings POPULATE_READ and POPULATE_WRITE is fastest. Note that Reading/POPULATE_READ will populate the shared zeropage where applicable -- which result in short population times. The fastest way to allocate backend storage (here: swap or huge pages) and prefault page tables is POPULATE_WRITE. V.2: Shared mappings fallocate() is fastest, however, doesn't prefault page tables. POPULATE_WRITE is faster than simple writes and read/writes. POPULATE_READ is faster than simple reads. Without a fd, the fastest way to allocate backend storage and prefault page tables is POPULATE_WRITE. With an fd, the fastest way is usually FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one exception are actual files: FALLOCATE+Read is slightly faster than FALLOCATE+POPULATE_READ. The fastest way to allocate backend storage prefault page tables is FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then, FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as dirty. v.3: Detailed results ================================================== 2 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 0.119 ms Anon 4 KiB : Write : 0.222 ms Anon 4 KiB : Read/Write : 0.380 ms Anon 4 KiB : POPULATE_READ : 0.060 ms Anon 4 KiB : POPULATE_WRITE : 0.158 ms Memfd 4 KiB : Read : 0.034 ms Memfd 4 KiB : Write : 0.310 ms Memfd 4 KiB : Read/Write : 0.362 ms Memfd 4 KiB : POPULATE_READ : 0.039 ms Memfd 4 KiB : POPULATE_WRITE : 0.229 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.033 ms tmpfs : Write : 0.313 ms tmpfs : Read/Write : 0.406 ms tmpfs : POPULATE_READ : 0.039 ms tmpfs : POPULATE_WRITE : 0.285 ms file : Read : 0.033 ms file : Write : 0.351 ms file : Read/Write : 0.408 ms file : POPULATE_READ : 0.039 ms file : POPULATE_WRITE : 0.290 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 237.940 ms Anon 4 KiB : Write : 708.409 ms Anon 4 KiB : Read/Write : 1054.041 ms Anon 4 KiB : POPULATE_READ : 124.310 ms Anon 4 KiB : POPULATE_WRITE : 572.582 ms Memfd 4 KiB : Read : 136.928 ms Memfd 4 KiB : Write : 963.898 ms Memfd 4 KiB : Read/Write : 1106.561 ms Memfd 4 KiB : POPULATE_READ : 78.450 ms Memfd 4 KiB : POPULATE_WRITE : 805.881 ms Memfd 2 MiB : Read : 357.116 ms Memfd 2 MiB : Write : 357.210 ms Memfd 2 MiB : Read/Write : 357.606 ms Memfd 2 MiB : POPULATE_READ : 356.094 ms Memfd 2 MiB : POPULATE_WRITE : 356.937 ms tmpfs : Read : 137.536 ms tmpfs : Write : 954.362 ms tmpfs : Read/Write : 1105.954 ms tmpfs : POPULATE_READ : 80.289 ms tmpfs : POPULATE_WRITE : 822.826 ms file : Read : 137.874 ms file : Write : 987.025 ms file : Read/Write : 1107.439 ms file : POPULATE_READ : 80.413 ms file : POPULATE_WRITE : 857.622 ms hugetlbfs : Read : 355.607 ms hugetlbfs : Write : 355.729 ms hugetlbfs : Read/Write : 356.127 ms hugetlbfs : POPULATE_READ : 354.585 ms hugetlbfs : POPULATE_WRITE : 355.138 ms ************************************************** 2 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 0.394 ms Anon 4 KiB : Write : 0.348 ms Anon 4 KiB : Read/Write : 0.400 ms Anon 4 KiB : POPULATE_READ : 0.326 ms Anon 4 KiB : POPULATE_WRITE : 0.273 ms Anon 2 MiB : Read : 0.030 ms Anon 2 MiB : Write : 0.030 ms Anon 2 MiB : Read/Write : 0.030 ms Anon 2 MiB : POPULATE_READ : 0.030 ms Anon 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 4 KiB : Read : 0.412 ms Memfd 4 KiB : Write : 0.372 ms Memfd 4 KiB : Read/Write : 0.419 ms Memfd 4 KiB : POPULATE_READ : 0.343 ms Memfd 4 KiB : POPULATE_WRITE : 0.288 ms Memfd 4 KiB : FALLOCATE : 0.137 ms Memfd 4 KiB : FALLOCATE+Read : 0.446 ms Memfd 4 KiB : FALLOCATE+Write : 0.330 ms Memfd 4 KiB : FALLOCATE+Read/Write : 0.454 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 0.379 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 0.268 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 2 MiB : FALLOCATE : 0.030 ms Memfd 2 MiB : FALLOCATE+Read : 0.031 ms Memfd 2 MiB : FALLOCATE+Write : 0.031 ms Memfd 2 MiB : FALLOCATE+Read/Write : 0.031 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 0.030 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.416 ms tmpfs : Write : 0.369 ms tmpfs : Read/Write : 0.425 ms tmpfs : POPULATE_READ : 0.346 ms tmpfs : POPULATE_WRITE : 0.295 ms tmpfs : FALLOCATE : 0.139 ms tmpfs : FALLOCATE+Read : 0.447 ms tmpfs : FALLOCATE+Write : 0.333 ms tmpfs : FALLOCATE+Read/Write : 0.454 ms tmpfs : FALLOCATE+POPULATE_READ : 0.380 ms tmpfs : FALLOCATE+POPULATE_WRITE : 0.272 ms file : Read : 0.191 ms file : Write : 0.511 ms file : Read/Write : 0.524 ms file : POPULATE_READ : 0.196 ms file : POPULATE_WRITE : 0.434 ms file : FALLOCATE : 0.004 ms file : FALLOCATE+Read : 0.197 ms file : FALLOCATE+Write : 0.554 ms file : FALLOCATE+Read/Write : 0.480 ms file : FALLOCATE+POPULATE_READ : 0.201 ms file : FALLOCATE+POPULATE_WRITE : 0.381 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms hugetlbfs : FALLOCATE : 0.030 ms hugetlbfs : FALLOCATE+Read : 0.031 ms hugetlbfs : FALLOCATE+Write : 0.031 ms hugetlbfs : FALLOCATE+Read/Write : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_READ : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 1053.090 ms Anon 4 KiB : Write : 913.642 ms Anon 4 KiB : Read/Write : 1060.350 ms Anon 4 KiB : POPULATE_READ : 893.691 ms Anon 4 KiB : POPULATE_WRITE : 782.885 ms Anon 2 MiB : Read : 358.553 ms Anon 2 MiB : Write : 358.419 ms Anon 2 MiB : Read/Write : 357.992 ms Anon 2 MiB : POPULATE_READ : 357.533 ms Anon 2 MiB : POPULATE_WRITE : 357.808 ms Memfd 4 KiB : Read : 1078.144 ms Memfd 4 KiB : Write : 942.036 ms Memfd 4 KiB : Read/Write : 1100.391 ms Memfd 4 KiB : POPULATE_READ : 925.829 ms Memfd 4 KiB : POPULATE_WRITE : 804.394 ms Memfd 4 KiB : FALLOCATE : 304.632 ms Memfd 4 KiB : FALLOCATE+Read : 1163.359 ms Memfd 4 KiB : FALLOCATE+Write : 933.186 ms Memfd 4 KiB : FALLOCATE+Read/Write : 1187.304 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 1013.660 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 794.560 ms Memfd 2 MiB : Read : 358.131 ms Memfd 2 MiB : Write : 358.099 ms Memfd 2 MiB : Read/Write : 358.250 ms Memfd 2 MiB : POPULATE_READ : 357.563 ms Memfd 2 MiB : POPULATE_WRITE : 357.334 ms Memfd 2 MiB : FALLOCATE : 356.735 ms Memfd 2 MiB : FALLOCATE+Read : 358.152 ms Memfd 2 MiB : FALLOCATE+Write : 358.331 ms Memfd 2 MiB : FALLOCATE+Read/Write : 358.018 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 357.286 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 357.523 ms tmpfs : Read : 1087.265 ms tmpfs : Write : 950.840 ms tmpfs : Read/Write : 1107.567 ms tmpfs : POPULATE_READ : 922.605 ms tmpfs : POPULATE_WRITE : 810.094 ms tmpfs : FALLOCATE : 306.320 ms tmpfs : FALLOCATE+Read : 1169.796 ms tmpfs : FALLOCATE+Write : 933.730 ms tmpfs : FALLOCATE+Read/Write : 1191.610 ms tmpfs : FALLOCATE+POPULATE_READ : 1020.474 ms tmpfs : FALLOCATE+POPULATE_WRITE : 798.945 ms file : Read : 654.101 ms file : Write : 1259.142 ms file : Read/Write : 1289.509 ms file : POPULATE_READ : 661.642 ms file : POPULATE_WRITE : 1106.816 ms file : FALLOCATE : 1.864 ms file : FALLOCATE+Read : 656.328 ms file : FALLOCATE+Write : 1153.300 ms file : FALLOCATE+Read/Write : 1180.613 ms file : FALLOCATE+POPULATE_READ : 668.347 ms file : FALLOCATE+POPULATE_WRITE : 996.143 ms hugetlbfs : Read : 357.245 ms hugetlbfs : Write : 357.413 ms hugetlbfs : Read/Write : 357.120 ms hugetlbfs : POPULATE_READ : 356.321 ms hugetlbfs : POPULATE_WRITE : 356.693 ms hugetlbfs : FALLOCATE : 355.927 ms hugetlbfs : FALLOCATE+Read : 357.074 ms hugetlbfs : FALLOCATE+Write : 357.120 ms hugetlbfs : FALLOCATE+Read/Write : 356.983 ms hugetlbfs : FALLOCATE+POPULATE_READ : 356.413 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 356.266 ms ************************************************** [1] https://lkml.org/lkml/2013/6/27/698 [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 09:52:28 +08:00
NULL, NULL, locked);
mm/munlock: add lru_add_drain() to fix memcg_stat_test Mike reports that LTP memcg_stat_test usually leads to memcg_stat_test 3 TINFO: Test unevictable with MAP_LOCKED memcg_stat_test 3 TINFO: Running memcg_process --mmap-lock1 -s 135168 memcg_stat_test 3 TINFO: Warming up pid: 3460 memcg_stat_test 3 TINFO: Process is still here after warm up: 3460 memcg_stat_test 3 TFAIL: unevictable is 122880, 135168 expected but may also lead to memcg_stat_test 4 TINFO: Test unevictable with mlock memcg_stat_test 4 TINFO: Running memcg_process --mmap-lock2 -s 135168 memcg_stat_test 4 TINFO: Warming up pid: 4271 memcg_stat_test 4 TINFO: Process is still here after warm up: 4271 memcg_stat_test 4 TFAIL: unevictable is 122880, 135168 expected or both. A wee bit flaky. follow_page_pte() used to have an lru_add_drain() per each page mlocked, and the test came to rely on accurate stats. The pagevec to be drained is different now, but still covered by lru_add_drain(); and, never mind the test, I believe it's in everyone's interest that a bulk faulting interface like populate_vma_page_range() or faultin_vma_page_range() should drain its local pagevecs at the end, to save others sometimes needing the much more expensive lru_add_drain_all(). This does not absolutely guarantee exact stats - the mlocking task can be migrated between CPUs as it proceeds - but it's good enough and the tests pass. Link: https://lkml.kernel.org/r/47f6d39c-a075-50cb-1cfb-26dd957a48af@google.com Fixes: b67bf49ce7aa ("mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE") Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Mike Galbraith <efault@gmx.de> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-04-02 02:28:27 +08:00
lru_add_drain();
return ret;
mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables I. Background: Sparse Memory Mappings When we manage sparse memory mappings dynamically in user space - also sometimes involving MAP_NORESERVE - we want to dynamically populate/ discard memory inside such a sparse memory region. Example users are hypervisors (especially implementing memory ballooning or similar technologies like virtio-mem) and memory allocators. In addition, we want to fail in a nice way (instead of generating SIGBUS) if populating does not succeed because we are out of backend memory (which can happen easily with file-based mappings, especially tmpfs and hugetlbfs). While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for reliably discarding memory for most mapping types, there is no generic approach to populate page tables and preallocate memory. Although mmap() supports MAP_POPULATE, it is not applicable to the concept of sparse memory mappings, where we want to populate/discard dynamically and avoid expensive/problematic remappings. In addition, we never actually report errors during the final populate phase - it is best-effort only. fallocate() can be used to preallocate file-based memory and fail in a safe way. However, it cannot really be used for any private mappings on anonymous files via memfd due to COW semantics. In addition, fallocate() does not actually populate page tables, so we still always get pagefaults on first access - which is sometimes undesired (i.e., real-time workloads) and requires real prefaulting of page tables, not just a preallocation of backend storage. There might be interesting use cases for sparse memory regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy as it does not prefault page tables. II. On preallcoation/prefaulting from user space Because we don't have a proper interface, what applications (like QEMU and databases) end up doing is touching (i.e., reading+writing one byte to not overwrite existing data) all individual pages. However, that approach 1) Can result in wear on storage backing, because we end up reading/writing each page; this is especially a problem for dax/pmem. 2) Can result in mmap_sem contention when prefaulting via multiple threads. 3) Requires expensive signal handling, especially to catch SIGBUS in case of hugetlbfs/shmem/file-backed memory. For example, this is problematic in hypervisors like QEMU where SIGBUS handlers might already be used by other subsystems concurrently to e.g, handle hardware errors. "Simply" doing preallocation concurrently from other thread is not that easy. III. On MADV_WILLNEED Extending MADV_WILLNEED is not an option because 1. It would change the semantics: "Expect access in the near future." and "might be a good idea to read some pages" vs. "Definitely populate/ preallocate all memory and definitely fail on errors.". 2. Existing users (like virtio-balloon in QEMU when deflating the balloon) don't want populate/prealloc semantics. They treat this rather as a hint to give a little performance boost without too much overhead - and don't expect that a lot of memory might get consumed or a lot of time might be spent. IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by MAP_POPULATE, with the following semantics: 1. MADV_POPULATE_READ can be used to prefault page tables just like manually reading each individual page. This will not break any COW mappings. The shared zero page might get mapped and no backend storage might get preallocated -- allocation might be deferred to write-fault time. Especially shared file mappings require an explicit fallocate() upfront to actually preallocate backend memory (blocks in the file system) in case the file might have holes. 2. If MADV_POPULATE_READ succeeds, all page tables have been populated (prefaulted) readable once. 3. MADV_POPULATE_WRITE can be used to preallocate backend memory and prefault page tables just like manually writing (or reading+writing) each individual page. This will break any COW mappings -- e.g., the shared zeropage is never populated. 4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated (prefaulted) writable once. 5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special mappings marked with VM_PFNMAP and VM_IO. Also, proper access permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such mapping is encountered, madvise() fails with -EINVAL. 6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables might have been populated. 7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON when encountering a HW poisoned page in the range. 8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot protect from the OOM (Out Of Memory) handler killing the process. While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e., preallocate memory and prefault page tables for VMs), one issue is that whenever we prefault pages writable, the pages have to be marked dirty, because the CPU could dirty them any time. while not a real problem for hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each page will be marked dirty and has to be written back later when evicting. MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole mapping from backend storage without marking it dirty, such that eviction won't have to write it back. As discussed above, shared file mappings might require an explciit fallocate() upfront to achieve preallcoation+prepopulation. Although sparse memory mappings are the primary use case, this will also be useful for other preallocate/prefault use cases where MAP_POPULATE is not desired or the semantics of MAP_POPULATE are not sufficient: as one example, QEMU users can trigger preallocation/prefaulting of guest RAM after the mapping was created -- and don't want errors to be silently suppressed. Looking at the history, MADV_POPULATE was already proposed in 2013 [1], however, the main motivation back than was performance improvements -- which should also still be the case. V. Single-threaded performance comparison I did a short experiment, prefaulting page tables on completely *empty mappings/files* and repeated the experiment 10 times. The results correspond to the shortest execution time. In general, the performance benefit for huge pages is negligible with small mappings. V.1: Private mappings POPULATE_READ and POPULATE_WRITE is fastest. Note that Reading/POPULATE_READ will populate the shared zeropage where applicable -- which result in short population times. The fastest way to allocate backend storage (here: swap or huge pages) and prefault page tables is POPULATE_WRITE. V.2: Shared mappings fallocate() is fastest, however, doesn't prefault page tables. POPULATE_WRITE is faster than simple writes and read/writes. POPULATE_READ is faster than simple reads. Without a fd, the fastest way to allocate backend storage and prefault page tables is POPULATE_WRITE. With an fd, the fastest way is usually FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one exception are actual files: FALLOCATE+Read is slightly faster than FALLOCATE+POPULATE_READ. The fastest way to allocate backend storage prefault page tables is FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then, FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as dirty. v.3: Detailed results ================================================== 2 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 0.119 ms Anon 4 KiB : Write : 0.222 ms Anon 4 KiB : Read/Write : 0.380 ms Anon 4 KiB : POPULATE_READ : 0.060 ms Anon 4 KiB : POPULATE_WRITE : 0.158 ms Memfd 4 KiB : Read : 0.034 ms Memfd 4 KiB : Write : 0.310 ms Memfd 4 KiB : Read/Write : 0.362 ms Memfd 4 KiB : POPULATE_READ : 0.039 ms Memfd 4 KiB : POPULATE_WRITE : 0.229 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.033 ms tmpfs : Write : 0.313 ms tmpfs : Read/Write : 0.406 ms tmpfs : POPULATE_READ : 0.039 ms tmpfs : POPULATE_WRITE : 0.285 ms file : Read : 0.033 ms file : Write : 0.351 ms file : Read/Write : 0.408 ms file : POPULATE_READ : 0.039 ms file : POPULATE_WRITE : 0.290 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_PRIVATE: ************************************************** Anon 4 KiB : Read : 237.940 ms Anon 4 KiB : Write : 708.409 ms Anon 4 KiB : Read/Write : 1054.041 ms Anon 4 KiB : POPULATE_READ : 124.310 ms Anon 4 KiB : POPULATE_WRITE : 572.582 ms Memfd 4 KiB : Read : 136.928 ms Memfd 4 KiB : Write : 963.898 ms Memfd 4 KiB : Read/Write : 1106.561 ms Memfd 4 KiB : POPULATE_READ : 78.450 ms Memfd 4 KiB : POPULATE_WRITE : 805.881 ms Memfd 2 MiB : Read : 357.116 ms Memfd 2 MiB : Write : 357.210 ms Memfd 2 MiB : Read/Write : 357.606 ms Memfd 2 MiB : POPULATE_READ : 356.094 ms Memfd 2 MiB : POPULATE_WRITE : 356.937 ms tmpfs : Read : 137.536 ms tmpfs : Write : 954.362 ms tmpfs : Read/Write : 1105.954 ms tmpfs : POPULATE_READ : 80.289 ms tmpfs : POPULATE_WRITE : 822.826 ms file : Read : 137.874 ms file : Write : 987.025 ms file : Read/Write : 1107.439 ms file : POPULATE_READ : 80.413 ms file : POPULATE_WRITE : 857.622 ms hugetlbfs : Read : 355.607 ms hugetlbfs : Write : 355.729 ms hugetlbfs : Read/Write : 356.127 ms hugetlbfs : POPULATE_READ : 354.585 ms hugetlbfs : POPULATE_WRITE : 355.138 ms ************************************************** 2 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 0.394 ms Anon 4 KiB : Write : 0.348 ms Anon 4 KiB : Read/Write : 0.400 ms Anon 4 KiB : POPULATE_READ : 0.326 ms Anon 4 KiB : POPULATE_WRITE : 0.273 ms Anon 2 MiB : Read : 0.030 ms Anon 2 MiB : Write : 0.030 ms Anon 2 MiB : Read/Write : 0.030 ms Anon 2 MiB : POPULATE_READ : 0.030 ms Anon 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 4 KiB : Read : 0.412 ms Memfd 4 KiB : Write : 0.372 ms Memfd 4 KiB : Read/Write : 0.419 ms Memfd 4 KiB : POPULATE_READ : 0.343 ms Memfd 4 KiB : POPULATE_WRITE : 0.288 ms Memfd 4 KiB : FALLOCATE : 0.137 ms Memfd 4 KiB : FALLOCATE+Read : 0.446 ms Memfd 4 KiB : FALLOCATE+Write : 0.330 ms Memfd 4 KiB : FALLOCATE+Read/Write : 0.454 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 0.379 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 0.268 ms Memfd 2 MiB : Read : 0.030 ms Memfd 2 MiB : Write : 0.030 ms Memfd 2 MiB : Read/Write : 0.030 ms Memfd 2 MiB : POPULATE_READ : 0.030 ms Memfd 2 MiB : POPULATE_WRITE : 0.030 ms Memfd 2 MiB : FALLOCATE : 0.030 ms Memfd 2 MiB : FALLOCATE+Read : 0.031 ms Memfd 2 MiB : FALLOCATE+Write : 0.031 ms Memfd 2 MiB : FALLOCATE+Read/Write : 0.031 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 0.030 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 0.030 ms tmpfs : Read : 0.416 ms tmpfs : Write : 0.369 ms tmpfs : Read/Write : 0.425 ms tmpfs : POPULATE_READ : 0.346 ms tmpfs : POPULATE_WRITE : 0.295 ms tmpfs : FALLOCATE : 0.139 ms tmpfs : FALLOCATE+Read : 0.447 ms tmpfs : FALLOCATE+Write : 0.333 ms tmpfs : FALLOCATE+Read/Write : 0.454 ms tmpfs : FALLOCATE+POPULATE_READ : 0.380 ms tmpfs : FALLOCATE+POPULATE_WRITE : 0.272 ms file : Read : 0.191 ms file : Write : 0.511 ms file : Read/Write : 0.524 ms file : POPULATE_READ : 0.196 ms file : POPULATE_WRITE : 0.434 ms file : FALLOCATE : 0.004 ms file : FALLOCATE+Read : 0.197 ms file : FALLOCATE+Write : 0.554 ms file : FALLOCATE+Read/Write : 0.480 ms file : FALLOCATE+POPULATE_READ : 0.201 ms file : FALLOCATE+POPULATE_WRITE : 0.381 ms hugetlbfs : Read : 0.030 ms hugetlbfs : Write : 0.030 ms hugetlbfs : Read/Write : 0.030 ms hugetlbfs : POPULATE_READ : 0.030 ms hugetlbfs : POPULATE_WRITE : 0.030 ms hugetlbfs : FALLOCATE : 0.030 ms hugetlbfs : FALLOCATE+Read : 0.031 ms hugetlbfs : FALLOCATE+Write : 0.031 ms hugetlbfs : FALLOCATE+Read/Write : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_READ : 0.030 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 0.030 ms ************************************************** 4096 MiB MAP_SHARED: ************************************************** Anon 4 KiB : Read : 1053.090 ms Anon 4 KiB : Write : 913.642 ms Anon 4 KiB : Read/Write : 1060.350 ms Anon 4 KiB : POPULATE_READ : 893.691 ms Anon 4 KiB : POPULATE_WRITE : 782.885 ms Anon 2 MiB : Read : 358.553 ms Anon 2 MiB : Write : 358.419 ms Anon 2 MiB : Read/Write : 357.992 ms Anon 2 MiB : POPULATE_READ : 357.533 ms Anon 2 MiB : POPULATE_WRITE : 357.808 ms Memfd 4 KiB : Read : 1078.144 ms Memfd 4 KiB : Write : 942.036 ms Memfd 4 KiB : Read/Write : 1100.391 ms Memfd 4 KiB : POPULATE_READ : 925.829 ms Memfd 4 KiB : POPULATE_WRITE : 804.394 ms Memfd 4 KiB : FALLOCATE : 304.632 ms Memfd 4 KiB : FALLOCATE+Read : 1163.359 ms Memfd 4 KiB : FALLOCATE+Write : 933.186 ms Memfd 4 KiB : FALLOCATE+Read/Write : 1187.304 ms Memfd 4 KiB : FALLOCATE+POPULATE_READ : 1013.660 ms Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 794.560 ms Memfd 2 MiB : Read : 358.131 ms Memfd 2 MiB : Write : 358.099 ms Memfd 2 MiB : Read/Write : 358.250 ms Memfd 2 MiB : POPULATE_READ : 357.563 ms Memfd 2 MiB : POPULATE_WRITE : 357.334 ms Memfd 2 MiB : FALLOCATE : 356.735 ms Memfd 2 MiB : FALLOCATE+Read : 358.152 ms Memfd 2 MiB : FALLOCATE+Write : 358.331 ms Memfd 2 MiB : FALLOCATE+Read/Write : 358.018 ms Memfd 2 MiB : FALLOCATE+POPULATE_READ : 357.286 ms Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 357.523 ms tmpfs : Read : 1087.265 ms tmpfs : Write : 950.840 ms tmpfs : Read/Write : 1107.567 ms tmpfs : POPULATE_READ : 922.605 ms tmpfs : POPULATE_WRITE : 810.094 ms tmpfs : FALLOCATE : 306.320 ms tmpfs : FALLOCATE+Read : 1169.796 ms tmpfs : FALLOCATE+Write : 933.730 ms tmpfs : FALLOCATE+Read/Write : 1191.610 ms tmpfs : FALLOCATE+POPULATE_READ : 1020.474 ms tmpfs : FALLOCATE+POPULATE_WRITE : 798.945 ms file : Read : 654.101 ms file : Write : 1259.142 ms file : Read/Write : 1289.509 ms file : POPULATE_READ : 661.642 ms file : POPULATE_WRITE : 1106.816 ms file : FALLOCATE : 1.864 ms file : FALLOCATE+Read : 656.328 ms file : FALLOCATE+Write : 1153.300 ms file : FALLOCATE+Read/Write : 1180.613 ms file : FALLOCATE+POPULATE_READ : 668.347 ms file : FALLOCATE+POPULATE_WRITE : 996.143 ms hugetlbfs : Read : 357.245 ms hugetlbfs : Write : 357.413 ms hugetlbfs : Read/Write : 357.120 ms hugetlbfs : POPULATE_READ : 356.321 ms hugetlbfs : POPULATE_WRITE : 356.693 ms hugetlbfs : FALLOCATE : 355.927 ms hugetlbfs : FALLOCATE+Read : 357.074 ms hugetlbfs : FALLOCATE+Write : 357.120 ms hugetlbfs : FALLOCATE+Read/Write : 356.983 ms hugetlbfs : FALLOCATE+POPULATE_READ : 356.413 ms hugetlbfs : FALLOCATE+POPULATE_WRITE : 356.266 ms ************************************************** [1] https://lkml.org/lkml/2013/6/27/698 [akpm@linux-foundation.org: coding style fixes] Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@surriel.com> Cc: Michael S. Tsirkin <mst@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com> Cc: Helge Deller <deller@gmx.de> Cc: Chris Zankel <chris@zankel.net> Cc: Max Filippov <jcmvbkbc@gmail.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rolf Eike Beer <eike-kernel@sf-tec.de> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 09:52:28 +08:00
}
/*
* __mm_populate - populate and/or mlock pages within a range of address space.
*
* This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
* flags. VMAs must be already marked with the desired vm_flags, and
* mmap_lock must not be held.
*/
int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
{
struct mm_struct *mm = current->mm;
unsigned long end, nstart, nend;
struct vm_area_struct *vma = NULL;
int locked = 0;
long ret = 0;
end = start + len;
for (nstart = start; nstart < end; nstart = nend) {
/*
* We want to fault in pages for [nstart; end) address range.
* Find first corresponding VMA.
*/
if (!locked) {
locked = 1;
mmap locking API: use coccinelle to convert mmap_sem rwsem call sites This change converts the existing mmap_sem rwsem calls to use the new mmap locking API instead. The change is generated using coccinelle with the following rule: // spatch --sp-file mmap_lock_api.cocci --in-place --include-headers --dir . @@ expression mm; @@ ( -init_rwsem +mmap_init_lock | -down_write +mmap_write_lock | -down_write_killable +mmap_write_lock_killable | -down_write_trylock +mmap_write_trylock | -up_write +mmap_write_unlock | -downgrade_write +mmap_write_downgrade | -down_read +mmap_read_lock | -down_read_killable +mmap_read_lock_killable | -down_read_trylock +mmap_read_trylock | -up_read +mmap_read_unlock ) -(&mm->mmap_sem) +(mm) Signed-off-by: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jerome Glisse <jglisse@redhat.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Liam Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ying Han <yinghan@google.com> Link: http://lkml.kernel.org/r/20200520052908.204642-5-walken@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-09 12:33:25 +08:00
mmap_read_lock(mm);
vma = find_vma_intersection(mm, nstart, end);
} else if (nstart >= vma->vm_end)
vma = find_vma_intersection(mm, vma->vm_end, end);
if (!vma)
break;
/*
* Set [nstart; nend) to intersection of desired address
* range with the first VMA. Also, skip undesirable VMA types.
*/
nend = min(end, vma->vm_end);
if (vma->vm_flags & (VM_IO | VM_PFNMAP))
continue;
if (nstart < vma->vm_start)
nstart = vma->vm_start;
/*
* Now fault in a range of pages. populate_vma_page_range()
* double checks the vma flags, so that it won't mlock pages
* if the vma was already munlocked.
*/
ret = populate_vma_page_range(vma, nstart, nend, &locked);
if (ret < 0) {
if (ignore_errors) {
ret = 0;
continue; /* continue at next VMA */
}
break;
}
nend = nstart + ret * PAGE_SIZE;
ret = 0;
}
if (locked)
mmap locking API: use coccinelle to convert mmap_sem rwsem call sites This change converts the existing mmap_sem rwsem calls to use the new mmap locking API instead. The change is generated using coccinelle with the following rule: // spatch --sp-file mmap_lock_api.cocci --in-place --include-headers --dir . @@ expression mm; @@ ( -init_rwsem +mmap_init_lock | -down_write +mmap_write_lock | -down_write_killable +mmap_write_lock_killable | -down_write_trylock +mmap_write_trylock | -up_write +mmap_write_unlock | -downgrade_write +mmap_write_downgrade | -down_read +mmap_read_lock | -down_read_killable +mmap_read_lock_killable | -down_read_trylock +mmap_read_trylock | -up_read +mmap_read_unlock ) -(&mm->mmap_sem) +(mm) Signed-off-by: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Davidlohr Bueso <dbueso@suse.de> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jerome Glisse <jglisse@redhat.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Liam Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ying Han <yinghan@google.com> Link: http://lkml.kernel.org/r/20200520052908.204642-5-walken@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-09 12:33:25 +08:00
mmap_read_unlock(mm);
return ret; /* 0 or negative error code */
}
#else /* CONFIG_MMU */
static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
unsigned long nr_pages, struct page **pages,
struct vm_area_struct **vmas, int *locked,
unsigned int foll_flags)
{
struct vm_area_struct *vma;
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
bool must_unlock = false;
unsigned long vm_flags;
long i;
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
if (!nr_pages)
return 0;
/*
* The internal caller expects GUP to manage the lock internally and the
* lock must be released when this returns.
*/
if (!*locked) {
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
if (mmap_read_lock_killable(mm))
return -EAGAIN;
must_unlock = true;
*locked = 1;
}
/* calculate required read or write permissions.
* If FOLL_FORCE is set, we only require the "MAY" flags.
*/
vm_flags = (foll_flags & FOLL_WRITE) ?
(VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
vm_flags &= (foll_flags & FOLL_FORCE) ?
(VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
for (i = 0; i < nr_pages; i++) {
vma = find_vma(mm, start);
if (!vma)
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
break;
/* protect what we can, including chardevs */
if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
!(vm_flags & vma->vm_flags))
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
break;
if (pages) {
pages[i] = virt_to_page((void *)start);
if (pages[i])
get_page(pages[i]);
}
if (vmas)
vmas[i] = vma;
start = (start + PAGE_SIZE) & PAGE_MASK;
}
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
if (must_unlock && *locked) {
mmap_read_unlock(mm);
*locked = 0;
}
return i ? : -EFAULT;
}
#endif /* !CONFIG_MMU */
/**
* fault_in_writeable - fault in userspace address range for writing
* @uaddr: start of address range
* @size: size of address range
*
* Returns the number of bytes not faulted in (like copy_to_user() and
* copy_from_user()).
*/
size_t fault_in_writeable(char __user *uaddr, size_t size)
{
char __user *start = uaddr, *end;
if (unlikely(size == 0))
return 0;
if (!user_write_access_begin(uaddr, size))
return size;
if (!PAGE_ALIGNED(uaddr)) {
unsafe_put_user(0, uaddr, out);
uaddr = (char __user *)PAGE_ALIGN((unsigned long)uaddr);
}
end = (char __user *)PAGE_ALIGN((unsigned long)start + size);
if (unlikely(end < start))
end = NULL;
while (uaddr != end) {
unsafe_put_user(0, uaddr, out);
uaddr += PAGE_SIZE;
}
out:
user_write_access_end();
if (size > uaddr - start)
return size - (uaddr - start);
return 0;
}
EXPORT_SYMBOL(fault_in_writeable);
/**
* fault_in_subpage_writeable - fault in an address range for writing
* @uaddr: start of address range
* @size: size of address range
*
* Fault in a user address range for writing while checking for permissions at
* sub-page granularity (e.g. arm64 MTE). This function should be used when
* the caller cannot guarantee forward progress of a copy_to_user() loop.
*
* Returns the number of bytes not faulted in (like copy_to_user() and
* copy_from_user()).
*/
size_t fault_in_subpage_writeable(char __user *uaddr, size_t size)
{
size_t faulted_in;
/*
* Attempt faulting in at page granularity first for page table
* permission checking. The arch-specific probe_subpage_writeable()
* functions may not check for this.
*/
faulted_in = size - fault_in_writeable(uaddr, size);
if (faulted_in)
faulted_in -= probe_subpage_writeable(uaddr, faulted_in);
return size - faulted_in;
}
EXPORT_SYMBOL(fault_in_subpage_writeable);
/*
* fault_in_safe_writeable - fault in an address range for writing
* @uaddr: start of address range
* @size: length of address range
*
* Faults in an address range for writing. This is primarily useful when we
* already know that some or all of the pages in the address range aren't in
* memory.
*
* Unlike fault_in_writeable(), this function is non-destructive.
*
* Note that we don't pin or otherwise hold the pages referenced that we fault
* in. There's no guarantee that they'll stay in memory for any duration of
* time.
*
* Returns the number of bytes not faulted in, like copy_to_user() and
* copy_from_user().
*/
size_t fault_in_safe_writeable(const char __user *uaddr, size_t size)
{
unsigned long start = (unsigned long)uaddr, end;
struct mm_struct *mm = current->mm;
bool unlocked = false;
if (unlikely(size == 0))
return 0;
end = PAGE_ALIGN(start + size);
if (end < start)
end = 0;
mmap_read_lock(mm);
do {
if (fixup_user_fault(mm, start, FAULT_FLAG_WRITE, &unlocked))
break;
start = (start + PAGE_SIZE) & PAGE_MASK;
} while (start != end);
mmap_read_unlock(mm);
if (size > (unsigned long)uaddr - start)
return size - ((unsigned long)uaddr - start);
return 0;
}
EXPORT_SYMBOL(fault_in_safe_writeable);
/**
* fault_in_readable - fault in userspace address range for reading
* @uaddr: start of user address range
* @size: size of user address range
*
* Returns the number of bytes not faulted in (like copy_to_user() and
* copy_from_user()).
*/
size_t fault_in_readable(const char __user *uaddr, size_t size)
{
const char __user *start = uaddr, *end;
volatile char c;
if (unlikely(size == 0))
return 0;
if (!user_read_access_begin(uaddr, size))
return size;
if (!PAGE_ALIGNED(uaddr)) {
unsafe_get_user(c, uaddr, out);
uaddr = (const char __user *)PAGE_ALIGN((unsigned long)uaddr);
}
end = (const char __user *)PAGE_ALIGN((unsigned long)start + size);
if (unlikely(end < start))
end = NULL;
while (uaddr != end) {
unsafe_get_user(c, uaddr, out);
uaddr += PAGE_SIZE;
}
out:
user_read_access_end();
(void)c;
if (size > uaddr - start)
return size - (uaddr - start);
return 0;
}
EXPORT_SYMBOL(fault_in_readable);
binfmt_elf_fdpic: stop using dump_emit() on user pointers on !MMU Patch series "Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there", v5. At the moment, we have that rather ugly mmget_still_valid() helper to work around <https://crbug.com/project-zero/1790>: ELF core dumping doesn't take the mmap_sem while traversing the task's VMAs, and if anything (like userfaultfd) then remotely messes with the VMA tree, fireworks ensue. So at the moment we use mmget_still_valid() to bail out in any writers that might be operating on a remote mm's VMAs. With this series, I'm trying to get rid of the need for that as cleanly as possible. ("cleanly" meaning "avoid holding the mmap_lock across unbounded sleeps".) Patches 1, 2, 3 and 4 are relatively unrelated cleanups in the core dumping code. Patches 5 and 6 implement the main change: Instead of repeatedly accessing the VMA list with sleeps in between, we snapshot it at the start with proper locking, and then later we just use our copy of the VMA list. This ensures that the kernel won't crash, that VMA metadata in the coredump is consistent even in the presence of concurrent modifications, and that any virtual addresses that aren't being concurrently modified have their contents show up in the core dump properly. The disadvantage of this approach is that we need a bit more memory during core dumping for storing metadata about all VMAs. At the end of the series, patch 7 removes the old workaround for this issue (mmget_still_valid()). I have tested: - Creating a simple core dump on X86-64 still works. - The created coredump on X86-64 opens in GDB and looks plausible. - X86-64 core dumps contain the first page for executable mappings at offset 0, and don't contain the first page for non-executable file mappings or executable mappings at offset !=0. - NOMMU 32-bit ARM can still generate plausible-looking core dumps through the FDPIC implementation. (I can't test this with GDB because GDB is missing some structure definition for nommu ARM, but I've poked around in the hexdump and it looked decent.) This patch (of 7): dump_emit() is for kernel pointers, and VMAs describe userspace memory. Let's be tidy here and avoid accessing userspace pointers under KERNEL_DS, even if it probably doesn't matter much on !MMU systems - especially given that it looks like we can just use the same get_dump_page() as on MMU if we move it out of the CONFIG_MMU block. One small change we have to make in get_dump_page() is to use __get_user_pages_locked() instead of __get_user_pages(), since the latter doesn't exist on nommu. On mmu builds, __get_user_pages_locked() will just call __get_user_pages() for us. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: "Eric W . Biederman" <ebiederm@xmission.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Hugh Dickins <hughd@google.com> Link: http://lkml.kernel.org/r/20200827114932.3572699-1-jannh@google.com Link: http://lkml.kernel.org/r/20200827114932.3572699-2-jannh@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-16 11:12:40 +08:00
/**
* get_dump_page() - pin user page in memory while writing it to core dump
* @addr: user address
*
* Returns struct page pointer of user page pinned for dump,
* to be freed afterwards by put_page().
*
* Returns NULL on any kind of failure - a hole must then be inserted into
* the corefile, to preserve alignment with its headers; and also returns
* NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
* allowing a hole to be left in the corefile to save disk space.
binfmt_elf_fdpic: stop using dump_emit() on user pointers on !MMU Patch series "Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there", v5. At the moment, we have that rather ugly mmget_still_valid() helper to work around <https://crbug.com/project-zero/1790>: ELF core dumping doesn't take the mmap_sem while traversing the task's VMAs, and if anything (like userfaultfd) then remotely messes with the VMA tree, fireworks ensue. So at the moment we use mmget_still_valid() to bail out in any writers that might be operating on a remote mm's VMAs. With this series, I'm trying to get rid of the need for that as cleanly as possible. ("cleanly" meaning "avoid holding the mmap_lock across unbounded sleeps".) Patches 1, 2, 3 and 4 are relatively unrelated cleanups in the core dumping code. Patches 5 and 6 implement the main change: Instead of repeatedly accessing the VMA list with sleeps in between, we snapshot it at the start with proper locking, and then later we just use our copy of the VMA list. This ensures that the kernel won't crash, that VMA metadata in the coredump is consistent even in the presence of concurrent modifications, and that any virtual addresses that aren't being concurrently modified have their contents show up in the core dump properly. The disadvantage of this approach is that we need a bit more memory during core dumping for storing metadata about all VMAs. At the end of the series, patch 7 removes the old workaround for this issue (mmget_still_valid()). I have tested: - Creating a simple core dump on X86-64 still works. - The created coredump on X86-64 opens in GDB and looks plausible. - X86-64 core dumps contain the first page for executable mappings at offset 0, and don't contain the first page for non-executable file mappings or executable mappings at offset !=0. - NOMMU 32-bit ARM can still generate plausible-looking core dumps through the FDPIC implementation. (I can't test this with GDB because GDB is missing some structure definition for nommu ARM, but I've poked around in the hexdump and it looked decent.) This patch (of 7): dump_emit() is for kernel pointers, and VMAs describe userspace memory. Let's be tidy here and avoid accessing userspace pointers under KERNEL_DS, even if it probably doesn't matter much on !MMU systems - especially given that it looks like we can just use the same get_dump_page() as on MMU if we move it out of the CONFIG_MMU block. One small change we have to make in get_dump_page() is to use __get_user_pages_locked() instead of __get_user_pages(), since the latter doesn't exist on nommu. On mmu builds, __get_user_pages_locked() will just call __get_user_pages() for us. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: "Eric W . Biederman" <ebiederm@xmission.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Hugh Dickins <hughd@google.com> Link: http://lkml.kernel.org/r/20200827114932.3572699-1-jannh@google.com Link: http://lkml.kernel.org/r/20200827114932.3572699-2-jannh@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-16 11:12:40 +08:00
*
* Called without mmap_lock (takes and releases the mmap_lock by itself).
binfmt_elf_fdpic: stop using dump_emit() on user pointers on !MMU Patch series "Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there", v5. At the moment, we have that rather ugly mmget_still_valid() helper to work around <https://crbug.com/project-zero/1790>: ELF core dumping doesn't take the mmap_sem while traversing the task's VMAs, and if anything (like userfaultfd) then remotely messes with the VMA tree, fireworks ensue. So at the moment we use mmget_still_valid() to bail out in any writers that might be operating on a remote mm's VMAs. With this series, I'm trying to get rid of the need for that as cleanly as possible. ("cleanly" meaning "avoid holding the mmap_lock across unbounded sleeps".) Patches 1, 2, 3 and 4 are relatively unrelated cleanups in the core dumping code. Patches 5 and 6 implement the main change: Instead of repeatedly accessing the VMA list with sleeps in between, we snapshot it at the start with proper locking, and then later we just use our copy of the VMA list. This ensures that the kernel won't crash, that VMA metadata in the coredump is consistent even in the presence of concurrent modifications, and that any virtual addresses that aren't being concurrently modified have their contents show up in the core dump properly. The disadvantage of this approach is that we need a bit more memory during core dumping for storing metadata about all VMAs. At the end of the series, patch 7 removes the old workaround for this issue (mmget_still_valid()). I have tested: - Creating a simple core dump on X86-64 still works. - The created coredump on X86-64 opens in GDB and looks plausible. - X86-64 core dumps contain the first page for executable mappings at offset 0, and don't contain the first page for non-executable file mappings or executable mappings at offset !=0. - NOMMU 32-bit ARM can still generate plausible-looking core dumps through the FDPIC implementation. (I can't test this with GDB because GDB is missing some structure definition for nommu ARM, but I've poked around in the hexdump and it looked decent.) This patch (of 7): dump_emit() is for kernel pointers, and VMAs describe userspace memory. Let's be tidy here and avoid accessing userspace pointers under KERNEL_DS, even if it probably doesn't matter much on !MMU systems - especially given that it looks like we can just use the same get_dump_page() as on MMU if we move it out of the CONFIG_MMU block. One small change we have to make in get_dump_page() is to use __get_user_pages_locked() instead of __get_user_pages(), since the latter doesn't exist on nommu. On mmu builds, __get_user_pages_locked() will just call __get_user_pages() for us. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: "Eric W . Biederman" <ebiederm@xmission.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Hugh Dickins <hughd@google.com> Link: http://lkml.kernel.org/r/20200827114932.3572699-1-jannh@google.com Link: http://lkml.kernel.org/r/20200827114932.3572699-2-jannh@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-16 11:12:40 +08:00
*/
#ifdef CONFIG_ELF_CORE
struct page *get_dump_page(unsigned long addr)
{
struct page *page;
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
int locked = 0;
int ret;
binfmt_elf_fdpic: stop using dump_emit() on user pointers on !MMU Patch series "Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there", v5. At the moment, we have that rather ugly mmget_still_valid() helper to work around <https://crbug.com/project-zero/1790>: ELF core dumping doesn't take the mmap_sem while traversing the task's VMAs, and if anything (like userfaultfd) then remotely messes with the VMA tree, fireworks ensue. So at the moment we use mmget_still_valid() to bail out in any writers that might be operating on a remote mm's VMAs. With this series, I'm trying to get rid of the need for that as cleanly as possible. ("cleanly" meaning "avoid holding the mmap_lock across unbounded sleeps".) Patches 1, 2, 3 and 4 are relatively unrelated cleanups in the core dumping code. Patches 5 and 6 implement the main change: Instead of repeatedly accessing the VMA list with sleeps in between, we snapshot it at the start with proper locking, and then later we just use our copy of the VMA list. This ensures that the kernel won't crash, that VMA metadata in the coredump is consistent even in the presence of concurrent modifications, and that any virtual addresses that aren't being concurrently modified have their contents show up in the core dump properly. The disadvantage of this approach is that we need a bit more memory during core dumping for storing metadata about all VMAs. At the end of the series, patch 7 removes the old workaround for this issue (mmget_still_valid()). I have tested: - Creating a simple core dump on X86-64 still works. - The created coredump on X86-64 opens in GDB and looks plausible. - X86-64 core dumps contain the first page for executable mappings at offset 0, and don't contain the first page for non-executable file mappings or executable mappings at offset !=0. - NOMMU 32-bit ARM can still generate plausible-looking core dumps through the FDPIC implementation. (I can't test this with GDB because GDB is missing some structure definition for nommu ARM, but I've poked around in the hexdump and it looked decent.) This patch (of 7): dump_emit() is for kernel pointers, and VMAs describe userspace memory. Let's be tidy here and avoid accessing userspace pointers under KERNEL_DS, even if it probably doesn't matter much on !MMU systems - especially given that it looks like we can just use the same get_dump_page() as on MMU if we move it out of the CONFIG_MMU block. One small change we have to make in get_dump_page() is to use __get_user_pages_locked() instead of __get_user_pages(), since the latter doesn't exist on nommu. On mmu builds, __get_user_pages_locked() will just call __get_user_pages() for us. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: "Eric W . Biederman" <ebiederm@xmission.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Hugh Dickins <hughd@google.com> Link: http://lkml.kernel.org/r/20200827114932.3572699-1-jannh@google.com Link: http://lkml.kernel.org/r/20200827114932.3572699-2-jannh@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-16 11:12:40 +08:00
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
ret = __get_user_pages_locked(current->mm, addr, 1, &page, NULL,
&locked,
FOLL_FORCE | FOLL_DUMP | FOLL_GET);
return (ret == 1) ? page : NULL;
binfmt_elf_fdpic: stop using dump_emit() on user pointers on !MMU Patch series "Fix ELF / FDPIC ELF core dumping, and use mmap_lock properly in there", v5. At the moment, we have that rather ugly mmget_still_valid() helper to work around <https://crbug.com/project-zero/1790>: ELF core dumping doesn't take the mmap_sem while traversing the task's VMAs, and if anything (like userfaultfd) then remotely messes with the VMA tree, fireworks ensue. So at the moment we use mmget_still_valid() to bail out in any writers that might be operating on a remote mm's VMAs. With this series, I'm trying to get rid of the need for that as cleanly as possible. ("cleanly" meaning "avoid holding the mmap_lock across unbounded sleeps".) Patches 1, 2, 3 and 4 are relatively unrelated cleanups in the core dumping code. Patches 5 and 6 implement the main change: Instead of repeatedly accessing the VMA list with sleeps in between, we snapshot it at the start with proper locking, and then later we just use our copy of the VMA list. This ensures that the kernel won't crash, that VMA metadata in the coredump is consistent even in the presence of concurrent modifications, and that any virtual addresses that aren't being concurrently modified have their contents show up in the core dump properly. The disadvantage of this approach is that we need a bit more memory during core dumping for storing metadata about all VMAs. At the end of the series, patch 7 removes the old workaround for this issue (mmget_still_valid()). I have tested: - Creating a simple core dump on X86-64 still works. - The created coredump on X86-64 opens in GDB and looks plausible. - X86-64 core dumps contain the first page for executable mappings at offset 0, and don't contain the first page for non-executable file mappings or executable mappings at offset !=0. - NOMMU 32-bit ARM can still generate plausible-looking core dumps through the FDPIC implementation. (I can't test this with GDB because GDB is missing some structure definition for nommu ARM, but I've poked around in the hexdump and it looked decent.) This patch (of 7): dump_emit() is for kernel pointers, and VMAs describe userspace memory. Let's be tidy here and avoid accessing userspace pointers under KERNEL_DS, even if it probably doesn't matter much on !MMU systems - especially given that it looks like we can just use the same get_dump_page() as on MMU if we move it out of the CONFIG_MMU block. One small change we have to make in get_dump_page() is to use __get_user_pages_locked() instead of __get_user_pages(), since the latter doesn't exist on nommu. On mmu builds, __get_user_pages_locked() will just call __get_user_pages() for us. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: "Eric W . Biederman" <ebiederm@xmission.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Hugh Dickins <hughd@google.com> Link: http://lkml.kernel.org/r/20200827114932.3572699-1-jannh@google.com Link: http://lkml.kernel.org/r/20200827114932.3572699-2-jannh@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-16 11:12:40 +08:00
}
#endif /* CONFIG_ELF_CORE */
#ifdef CONFIG_MIGRATION
/*
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* Returns the number of collected pages. Return value is always >= 0.
*/
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static unsigned long collect_longterm_unpinnable_pages(
struct list_head *movable_page_list,
unsigned long nr_pages,
struct page **pages)
{
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unsigned long i, collected = 0;
struct folio *prev_folio = NULL;
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bool drain_allow = true;
mm/gup: check every subpage of a compound page during isolation When pages are isolated in check_and_migrate_movable_pages() we skip compound number of pages at a time. However, as Jason noted, it is not necessary correct that pages[i] corresponds to the pages that we skipped. This is because it is possible that the addresses in this range had split_huge_pmd()/split_huge_pud(), and these functions do not update the compound page metadata. The problem can be reproduced if something like this occurs: 1. User faulted huge pages. 2. split_huge_pmd() was called for some reason 3. User has unmapped some sub-pages in the range 4. User tries to longterm pin the addresses. The resulting pages[i] might end-up having pages which are not compound size page aligned. Link: https://lkml.kernel.org/r/20210215161349.246722-3-pasha.tatashin@soleen.com Fixes: aa712399c1e8 ("mm/gup: speed up check_and_migrate_cma_pages() on huge page") Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com> Reported-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: James Morris <jmorris@namei.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sasha Levin <sashal@kernel.org> Cc: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Tyler Hicks <tyhicks@linux.microsoft.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-05 09:38:42 +08:00
for (i = 0; i < nr_pages; i++) {
struct folio *folio = page_folio(pages[i]);
if (folio == prev_folio)
mm/gup: check every subpage of a compound page during isolation When pages are isolated in check_and_migrate_movable_pages() we skip compound number of pages at a time. However, as Jason noted, it is not necessary correct that pages[i] corresponds to the pages that we skipped. This is because it is possible that the addresses in this range had split_huge_pmd()/split_huge_pud(), and these functions do not update the compound page metadata. The problem can be reproduced if something like this occurs: 1. User faulted huge pages. 2. split_huge_pmd() was called for some reason 3. User has unmapped some sub-pages in the range 4. User tries to longterm pin the addresses. The resulting pages[i] might end-up having pages which are not compound size page aligned. Link: https://lkml.kernel.org/r/20210215161349.246722-3-pasha.tatashin@soleen.com Fixes: aa712399c1e8 ("mm/gup: speed up check_and_migrate_cma_pages() on huge page") Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com> Reported-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: James Morris <jmorris@namei.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sasha Levin <sashal@kernel.org> Cc: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Tyler Hicks <tyhicks@linux.microsoft.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-05 09:38:42 +08:00
continue;
prev_folio = folio;
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if (folio_is_longterm_pinnable(folio))
continue;
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collected++;
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if (folio_is_device_coherent(folio))
continue;
if (folio_test_hugetlb(folio)) {
isolate_hugetlb(folio, movable_page_list);
continue;
}
if (!folio_test_lru(folio) && drain_allow) {
lru_add_drain_all();
drain_allow = false;
}
mm: change to return bool for folio_isolate_lru() Patch series "Change the return value for page isolation functions", v3. Now the page isolation functions did not return a boolean to indicate success or not, instead it will return a negative error when failed to isolate a page. So below code used in most places seem a boolean success/failure thing, which can confuse people whether the isolation is successful. if (folio_isolate_lru(folio)) continue; Moreover the page isolation functions only return 0 or -EBUSY, and most users did not care about the negative error except for few users, thus we can convert all page isolation functions to return a boolean value, which can remove the confusion to make code more clear. No functional changes intended in this patch series. This patch (of 4): Now the folio_isolate_lru() did not return a boolean value to indicate isolation success or not, however below code checking the return value can make people think that it was a boolean success/failure thing, which makes people easy to make mistakes (see the fix patch[1]). if (folio_isolate_lru(folio)) continue; Thus it's better to check the negative error value expilictly returned by folio_isolate_lru(), which makes code more clear per Linus's suggestion[2]. Moreover Matthew suggested we can convert the isolation functions to return a boolean[3], since most users did not care about the negative error value, and can also remove the confusing of checking return value. So this patch converts the folio_isolate_lru() to return a boolean value, which means return 'true' to indicate the folio isolation is successful, and 'false' means a failure to isolation. Meanwhile changing all users' logic of checking the isolation state. No functional changes intended. [1] https://lore.kernel.org/all/20230131063206.28820-1-Kuan-Ying.Lee@mediatek.com/T/#u [2] https://lore.kernel.org/all/CAHk-=wiBrY+O-4=2mrbVyxR+hOqfdJ=Do6xoucfJ9_5az01L4Q@mail.gmail.com/ [3] https://lore.kernel.org/all/Y+sTFqwMNAjDvxw3@casper.infradead.org/ Link: https://lkml.kernel.org/r/cover.1676424378.git.baolin.wang@linux.alibaba.com Link: https://lkml.kernel.org/r/8a4e3679ed4196168efadf7ea36c038f2f7d5aa9.1676424378.git.baolin.wang@linux.alibaba.com Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: SeongJae Park <sj@kernel.org> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Miaohe Lin <linmiaohe@huawei.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Shakeel Butt <shakeelb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-02-15 18:39:34 +08:00
if (!folio_isolate_lru(folio))
continue;
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list_add_tail(&folio->lru, movable_page_list);
node_stat_mod_folio(folio,
NR_ISOLATED_ANON + folio_is_file_lru(folio),
folio_nr_pages(folio));
}
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return collected;
}
/*
* Unpins all pages and migrates device coherent pages and movable_page_list.
* Returns -EAGAIN if all pages were successfully migrated or -errno for failure
* (or partial success).
*/
static int migrate_longterm_unpinnable_pages(
struct list_head *movable_page_list,
unsigned long nr_pages,
struct page **pages)
{
int ret;
unsigned long i;
mm/gup: check for isolation errors It is still possible that we pin movable CMA pages if there are isolation errors and cma_page_list stays empty when we check again. Check for isolation errors, and return success only when there are no isolation errors, and cma_page_list is empty after checking. Because isolation errors are transient, we retry indefinitely. Link: https://lkml.kernel.org/r/20210215161349.246722-5-pasha.tatashin@soleen.com Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: James Morris <jmorris@namei.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sasha Levin <sashal@kernel.org> Cc: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Tyler Hicks <tyhicks@linux.microsoft.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-05 09:38:49 +08:00
for (i = 0; i < nr_pages; i++) {
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struct folio *folio = page_folio(pages[i]);
if (folio_is_device_coherent(folio)) {
/*
* Migration will fail if the page is pinned, so convert
* the pin on the source page to a normal reference.
*/
pages[i] = NULL;
folio_get(folio);
gup_put_folio(folio, 1, FOLL_PIN);
if (migrate_device_coherent_page(&folio->page)) {
ret = -EBUSY;
goto err;
}
continue;
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}
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/*
* We can't migrate pages with unexpected references, so drop
* the reference obtained by __get_user_pages_locked().
* Migrating pages have been added to movable_page_list after
* calling folio_isolate_lru() which takes a reference so the
* page won't be freed if it's migrating.
*/
unpin_user_page(pages[i]);
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pages[i] = NULL;
}
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if (!list_empty(movable_page_list)) {
struct migration_target_control mtc = {
.nid = NUMA_NO_NODE,
.gfp_mask = GFP_USER | __GFP_NOWARN,
};
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if (migrate_pages(movable_page_list, alloc_migration_target,
NULL, (unsigned long)&mtc, MIGRATE_SYNC,
MR_LONGTERM_PIN, NULL)) {
ret = -ENOMEM;
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goto err;
}
}
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putback_movable_pages(movable_page_list);
return -EAGAIN;
err:
for (i = 0; i < nr_pages; i++)
if (pages[i])
unpin_user_page(pages[i]);
putback_movable_pages(movable_page_list);
mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. This is indicated by returning zero. When all pages are in the correct zone the number of pinned pages is returned. However migration can also fail, in which case pages are unpinned and -ENOMEM is returned. However if the failure was due to not being unable to isolate a page zero is returned. This leads to indefinite looping in __gup_longterm_locked(). Fix this by simplifying the return codes such that zero indicates all pages were successfully pinned in the correct zone while errors indicate either pages were migrated and pinning should be retried or that migration has failed and therefore the pinning operation should fail. [syoshida@redhat.com: fix return value for __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220821183547.950370-1-syoshida@redhat.com [akpm@linux-foundation.org: fix code layout, per John] [yshigeru@gmail.com: fix uninitialized return value on __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220827230037.78876-1-syoshida@redhat.com Link: https://lkml.kernel.org/r/20220729024645.764366-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-29 10:46:45 +08:00
2022-08-24 13:09:52 +08:00
return ret;
}
/*
* Check whether all pages are *allowed* to be pinned. Rather confusingly, all
* pages in the range are required to be pinned via FOLL_PIN, before calling
* this routine.
*
* If any pages in the range are not allowed to be pinned, then this routine
* will migrate those pages away, unpin all the pages in the range and return
* -EAGAIN. The caller should re-pin the entire range with FOLL_PIN and then
* call this routine again.
*
* If an error other than -EAGAIN occurs, this indicates a migration failure.
* The caller should give up, and propagate the error back up the call stack.
*
* If everything is OK and all pages in the range are allowed to be pinned, then
* this routine leaves all pages pinned and returns zero for success.
*/
static long check_and_migrate_movable_pages(unsigned long nr_pages,
struct page **pages)
{
unsigned long collected;
LIST_HEAD(movable_page_list);
collected = collect_longterm_unpinnable_pages(&movable_page_list,
nr_pages, pages);
if (!collected)
return 0;
return migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages,
pages);
}
#else
static long check_and_migrate_movable_pages(unsigned long nr_pages,
struct page **pages)
{
mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. This is indicated by returning zero. When all pages are in the correct zone the number of pinned pages is returned. However migration can also fail, in which case pages are unpinned and -ENOMEM is returned. However if the failure was due to not being unable to isolate a page zero is returned. This leads to indefinite looping in __gup_longterm_locked(). Fix this by simplifying the return codes such that zero indicates all pages were successfully pinned in the correct zone while errors indicate either pages were migrated and pinning should be retried or that migration has failed and therefore the pinning operation should fail. [syoshida@redhat.com: fix return value for __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220821183547.950370-1-syoshida@redhat.com [akpm@linux-foundation.org: fix code layout, per John] [yshigeru@gmail.com: fix uninitialized return value on __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220827230037.78876-1-syoshida@redhat.com Link: https://lkml.kernel.org/r/20220729024645.764366-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-29 10:46:45 +08:00
return 0;
}
#endif /* CONFIG_MIGRATION */
mm: introduce get_user_pages_longterm Patch series "introduce get_user_pages_longterm()", v2. Here is a new get_user_pages api for cases where a driver intends to keep an elevated page count indefinitely. This is distinct from usages like iov_iter_get_pages where the elevated page counts are transient. The iov_iter_get_pages cases immediately turn around and submit the pages to a device driver which will put_page when the i/o operation completes (under kernel control). In the longterm case userspace is responsible for dropping the page reference at some undefined point in the future. This is untenable for filesystem-dax case where the filesystem is in control of the lifetime of the block / page and needs reasonable limits on how long it can wait for pages in a mapping to become idle. Fixing filesystems to actually wait for dax pages to be idle before blocks from a truncate/hole-punch operation are repurposed is saved for a later patch series. Also, allowing longterm registration of dax mappings is a future patch series that introduces a "map with lease" semantic where the kernel can revoke a lease and force userspace to drop its page references. I have also tagged these for -stable to purposely break cases that might assume that longterm memory registrations for filesystem-dax mappings were supported by the kernel. The behavior regression this policy change implies is one of the reasons we maintain the "dax enabled. Warning: EXPERIMENTAL, use at your own risk" notification when mounting a filesystem in dax mode. It is worth noting the device-dax interface does not suffer the same constraints since it does not support file space management operations like hole-punch. This patch (of 4): Until there is a solution to the dma-to-dax vs truncate problem it is not safe to allow long standing memory registrations against filesytem-dax vmas. Device-dax vmas do not have this problem and are explicitly allowed. This is temporary until a "memory registration with layout-lease" mechanism can be implemented for the affected sub-systems (RDMA and V4L2). [akpm@linux-foundation.org: use kcalloc()] Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Dan Williams <dan.j.williams@intel.com> Suggested-by: Christoph Hellwig <hch@lst.de> Cc: Doug Ledford <dledford@redhat.com> Cc: Hal Rosenstock <hal.rosenstock@gmail.com> Cc: Inki Dae <inki.dae@samsung.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Joonyoung Shim <jy0922.shim@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Sean Hefty <sean.hefty@intel.com> Cc: Seung-Woo Kim <sw0312.kim@samsung.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-30 08:10:35 +08:00
/*
mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM Pach series "Add FOLL_LONGTERM to GUP fast and use it". HFI1, qib, and mthca, use get_user_pages_fast() due to its performance advantages. These pages can be held for a significant time. But get_user_pages_fast() does not protect against mapping FS DAX pages. Introduce FOLL_LONGTERM and use this flag in get_user_pages_fast() which retains the performance while also adding the FS DAX checks. XDP has also shown interest in using this functionality.[1] In addition we change get_user_pages() to use the new FOLL_LONGTERM flag and remove the specialized get_user_pages_longterm call. [1] https://lkml.org/lkml/2019/3/19/939 "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Secondly, it depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an aside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. This patch (of 7): This patch starts a series which aims to support FOLL_LONGTERM in get_user_pages_fast(). Some callers who would like to do a longterm (user controlled pin) of pages with the fast variant of GUP for performance purposes. Rather than have a separate get_user_pages_longterm() call, introduce FOLL_LONGTERM and change the longterm callers to use it. This patch does not change any functionality. In the short term "longterm" or user controlled pins are unsafe for Filesystems and FS DAX in particular has been blocked. However, callers of get_user_pages_fast() were not "protected". FOLL_LONGTERM can _only_ be supported with get_user_pages[_fast]() as it requires vmas to determine if DAX is in use. NOTE: In merging with the CMA changes we opt to change the get_user_pages() call in check_and_migrate_cma_pages() to a call of __get_user_pages_locked() on the newly migrated pages. This makes the code read better in that we are calling __get_user_pages_locked() on the pages before and after a potential migration. As a side affect some of the interfaces are cleaned up but this is not the primary purpose of the series. In review[1] it was asked: <quote> > This I don't get - if you do lock down long term mappings performance > of the actual get_user_pages call shouldn't matter to start with. > > What do I miss? A couple of points. First "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Second, It depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an asside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. </quote> [1] https://lore.kernel.org/lkml/20190220180255.GA12020@iweiny-DESK2.sc.intel.com/T/#md6abad2569f3bf6c1f03686c8097ab6563e94965 [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-2-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Rich Felker <dalias@libc.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: James Hogan <jhogan@kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:03 +08:00
* __gup_longterm_locked() is a wrapper for __get_user_pages_locked which
* allows us to process the FOLL_LONGTERM flag.
mm: introduce get_user_pages_longterm Patch series "introduce get_user_pages_longterm()", v2. Here is a new get_user_pages api for cases where a driver intends to keep an elevated page count indefinitely. This is distinct from usages like iov_iter_get_pages where the elevated page counts are transient. The iov_iter_get_pages cases immediately turn around and submit the pages to a device driver which will put_page when the i/o operation completes (under kernel control). In the longterm case userspace is responsible for dropping the page reference at some undefined point in the future. This is untenable for filesystem-dax case where the filesystem is in control of the lifetime of the block / page and needs reasonable limits on how long it can wait for pages in a mapping to become idle. Fixing filesystems to actually wait for dax pages to be idle before blocks from a truncate/hole-punch operation are repurposed is saved for a later patch series. Also, allowing longterm registration of dax mappings is a future patch series that introduces a "map with lease" semantic where the kernel can revoke a lease and force userspace to drop its page references. I have also tagged these for -stable to purposely break cases that might assume that longterm memory registrations for filesystem-dax mappings were supported by the kernel. The behavior regression this policy change implies is one of the reasons we maintain the "dax enabled. Warning: EXPERIMENTAL, use at your own risk" notification when mounting a filesystem in dax mode. It is worth noting the device-dax interface does not suffer the same constraints since it does not support file space management operations like hole-punch. This patch (of 4): Until there is a solution to the dma-to-dax vs truncate problem it is not safe to allow long standing memory registrations against filesytem-dax vmas. Device-dax vmas do not have this problem and are explicitly allowed. This is temporary until a "memory registration with layout-lease" mechanism can be implemented for the affected sub-systems (RDMA and V4L2). [akpm@linux-foundation.org: use kcalloc()] Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Dan Williams <dan.j.williams@intel.com> Suggested-by: Christoph Hellwig <hch@lst.de> Cc: Doug Ledford <dledford@redhat.com> Cc: Hal Rosenstock <hal.rosenstock@gmail.com> Cc: Inki Dae <inki.dae@samsung.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Joonyoung Shim <jy0922.shim@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Sean Hefty <sean.hefty@intel.com> Cc: Seung-Woo Kim <sw0312.kim@samsung.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-30 08:10:35 +08:00
*/
static long __gup_longterm_locked(struct mm_struct *mm,
mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM Pach series "Add FOLL_LONGTERM to GUP fast and use it". HFI1, qib, and mthca, use get_user_pages_fast() due to its performance advantages. These pages can be held for a significant time. But get_user_pages_fast() does not protect against mapping FS DAX pages. Introduce FOLL_LONGTERM and use this flag in get_user_pages_fast() which retains the performance while also adding the FS DAX checks. XDP has also shown interest in using this functionality.[1] In addition we change get_user_pages() to use the new FOLL_LONGTERM flag and remove the specialized get_user_pages_longterm call. [1] https://lkml.org/lkml/2019/3/19/939 "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Secondly, it depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an aside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. This patch (of 7): This patch starts a series which aims to support FOLL_LONGTERM in get_user_pages_fast(). Some callers who would like to do a longterm (user controlled pin) of pages with the fast variant of GUP for performance purposes. Rather than have a separate get_user_pages_longterm() call, introduce FOLL_LONGTERM and change the longterm callers to use it. This patch does not change any functionality. In the short term "longterm" or user controlled pins are unsafe for Filesystems and FS DAX in particular has been blocked. However, callers of get_user_pages_fast() were not "protected". FOLL_LONGTERM can _only_ be supported with get_user_pages[_fast]() as it requires vmas to determine if DAX is in use. NOTE: In merging with the CMA changes we opt to change the get_user_pages() call in check_and_migrate_cma_pages() to a call of __get_user_pages_locked() on the newly migrated pages. This makes the code read better in that we are calling __get_user_pages_locked() on the pages before and after a potential migration. As a side affect some of the interfaces are cleaned up but this is not the primary purpose of the series. In review[1] it was asked: <quote> > This I don't get - if you do lock down long term mappings performance > of the actual get_user_pages call shouldn't matter to start with. > > What do I miss? A couple of points. First "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Second, It depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an asside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. </quote> [1] https://lore.kernel.org/lkml/20190220180255.GA12020@iweiny-DESK2.sc.intel.com/T/#md6abad2569f3bf6c1f03686c8097ab6563e94965 [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-2-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Rich Felker <dalias@libc.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: James Hogan <jhogan@kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:03 +08:00
unsigned long start,
unsigned long nr_pages,
struct page **pages,
struct vm_area_struct **vmas,
int *locked,
mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM Pach series "Add FOLL_LONGTERM to GUP fast and use it". HFI1, qib, and mthca, use get_user_pages_fast() due to its performance advantages. These pages can be held for a significant time. But get_user_pages_fast() does not protect against mapping FS DAX pages. Introduce FOLL_LONGTERM and use this flag in get_user_pages_fast() which retains the performance while also adding the FS DAX checks. XDP has also shown interest in using this functionality.[1] In addition we change get_user_pages() to use the new FOLL_LONGTERM flag and remove the specialized get_user_pages_longterm call. [1] https://lkml.org/lkml/2019/3/19/939 "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Secondly, it depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an aside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. This patch (of 7): This patch starts a series which aims to support FOLL_LONGTERM in get_user_pages_fast(). Some callers who would like to do a longterm (user controlled pin) of pages with the fast variant of GUP for performance purposes. Rather than have a separate get_user_pages_longterm() call, introduce FOLL_LONGTERM and change the longterm callers to use it. This patch does not change any functionality. In the short term "longterm" or user controlled pins are unsafe for Filesystems and FS DAX in particular has been blocked. However, callers of get_user_pages_fast() were not "protected". FOLL_LONGTERM can _only_ be supported with get_user_pages[_fast]() as it requires vmas to determine if DAX is in use. NOTE: In merging with the CMA changes we opt to change the get_user_pages() call in check_and_migrate_cma_pages() to a call of __get_user_pages_locked() on the newly migrated pages. This makes the code read better in that we are calling __get_user_pages_locked() on the pages before and after a potential migration. As a side affect some of the interfaces are cleaned up but this is not the primary purpose of the series. In review[1] it was asked: <quote> > This I don't get - if you do lock down long term mappings performance > of the actual get_user_pages call shouldn't matter to start with. > > What do I miss? A couple of points. First "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Second, It depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an asside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. </quote> [1] https://lore.kernel.org/lkml/20190220180255.GA12020@iweiny-DESK2.sc.intel.com/T/#md6abad2569f3bf6c1f03686c8097ab6563e94965 [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-2-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Rich Felker <dalias@libc.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: James Hogan <jhogan@kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:03 +08:00
unsigned int gup_flags)
mm: introduce get_user_pages_longterm Patch series "introduce get_user_pages_longterm()", v2. Here is a new get_user_pages api for cases where a driver intends to keep an elevated page count indefinitely. This is distinct from usages like iov_iter_get_pages where the elevated page counts are transient. The iov_iter_get_pages cases immediately turn around and submit the pages to a device driver which will put_page when the i/o operation completes (under kernel control). In the longterm case userspace is responsible for dropping the page reference at some undefined point in the future. This is untenable for filesystem-dax case where the filesystem is in control of the lifetime of the block / page and needs reasonable limits on how long it can wait for pages in a mapping to become idle. Fixing filesystems to actually wait for dax pages to be idle before blocks from a truncate/hole-punch operation are repurposed is saved for a later patch series. Also, allowing longterm registration of dax mappings is a future patch series that introduces a "map with lease" semantic where the kernel can revoke a lease and force userspace to drop its page references. I have also tagged these for -stable to purposely break cases that might assume that longterm memory registrations for filesystem-dax mappings were supported by the kernel. The behavior regression this policy change implies is one of the reasons we maintain the "dax enabled. Warning: EXPERIMENTAL, use at your own risk" notification when mounting a filesystem in dax mode. It is worth noting the device-dax interface does not suffer the same constraints since it does not support file space management operations like hole-punch. This patch (of 4): Until there is a solution to the dma-to-dax vs truncate problem it is not safe to allow long standing memory registrations against filesytem-dax vmas. Device-dax vmas do not have this problem and are explicitly allowed. This is temporary until a "memory registration with layout-lease" mechanism can be implemented for the affected sub-systems (RDMA and V4L2). [akpm@linux-foundation.org: use kcalloc()] Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Dan Williams <dan.j.williams@intel.com> Suggested-by: Christoph Hellwig <hch@lst.de> Cc: Doug Ledford <dledford@redhat.com> Cc: Hal Rosenstock <hal.rosenstock@gmail.com> Cc: Inki Dae <inki.dae@samsung.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Joonyoung Shim <jy0922.shim@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Sean Hefty <sean.hefty@intel.com> Cc: Seung-Woo Kim <sw0312.kim@samsung.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-30 08:10:35 +08:00
{
unsigned int flags;
mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. This is indicated by returning zero. When all pages are in the correct zone the number of pinned pages is returned. However migration can also fail, in which case pages are unpinned and -ENOMEM is returned. However if the failure was due to not being unable to isolate a page zero is returned. This leads to indefinite looping in __gup_longterm_locked(). Fix this by simplifying the return codes such that zero indicates all pages were successfully pinned in the correct zone while errors indicate either pages were migrated and pinning should be retried or that migration has failed and therefore the pinning operation should fail. [syoshida@redhat.com: fix return value for __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220821183547.950370-1-syoshida@redhat.com [akpm@linux-foundation.org: fix code layout, per John] [yshigeru@gmail.com: fix uninitialized return value on __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220827230037.78876-1-syoshida@redhat.com Link: https://lkml.kernel.org/r/20220729024645.764366-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-29 10:46:45 +08:00
long rc, nr_pinned_pages;
mm: introduce get_user_pages_longterm Patch series "introduce get_user_pages_longterm()", v2. Here is a new get_user_pages api for cases where a driver intends to keep an elevated page count indefinitely. This is distinct from usages like iov_iter_get_pages where the elevated page counts are transient. The iov_iter_get_pages cases immediately turn around and submit the pages to a device driver which will put_page when the i/o operation completes (under kernel control). In the longterm case userspace is responsible for dropping the page reference at some undefined point in the future. This is untenable for filesystem-dax case where the filesystem is in control of the lifetime of the block / page and needs reasonable limits on how long it can wait for pages in a mapping to become idle. Fixing filesystems to actually wait for dax pages to be idle before blocks from a truncate/hole-punch operation are repurposed is saved for a later patch series. Also, allowing longterm registration of dax mappings is a future patch series that introduces a "map with lease" semantic where the kernel can revoke a lease and force userspace to drop its page references. I have also tagged these for -stable to purposely break cases that might assume that longterm memory registrations for filesystem-dax mappings were supported by the kernel. The behavior regression this policy change implies is one of the reasons we maintain the "dax enabled. Warning: EXPERIMENTAL, use at your own risk" notification when mounting a filesystem in dax mode. It is worth noting the device-dax interface does not suffer the same constraints since it does not support file space management operations like hole-punch. This patch (of 4): Until there is a solution to the dma-to-dax vs truncate problem it is not safe to allow long standing memory registrations against filesytem-dax vmas. Device-dax vmas do not have this problem and are explicitly allowed. This is temporary until a "memory registration with layout-lease" mechanism can be implemented for the affected sub-systems (RDMA and V4L2). [akpm@linux-foundation.org: use kcalloc()] Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Dan Williams <dan.j.williams@intel.com> Suggested-by: Christoph Hellwig <hch@lst.de> Cc: Doug Ledford <dledford@redhat.com> Cc: Hal Rosenstock <hal.rosenstock@gmail.com> Cc: Inki Dae <inki.dae@samsung.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Joonyoung Shim <jy0922.shim@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Sean Hefty <sean.hefty@intel.com> Cc: Seung-Woo Kim <sw0312.kim@samsung.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-30 08:10:35 +08:00
if (!(gup_flags & FOLL_LONGTERM))
return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
locked, gup_flags);
2022-08-24 13:09:52 +08:00
flags = memalloc_pin_save();
do {
mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. This is indicated by returning zero. When all pages are in the correct zone the number of pinned pages is returned. However migration can also fail, in which case pages are unpinned and -ENOMEM is returned. However if the failure was due to not being unable to isolate a page zero is returned. This leads to indefinite looping in __gup_longterm_locked(). Fix this by simplifying the return codes such that zero indicates all pages were successfully pinned in the correct zone while errors indicate either pages were migrated and pinning should be retried or that migration has failed and therefore the pinning operation should fail. [syoshida@redhat.com: fix return value for __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220821183547.950370-1-syoshida@redhat.com [akpm@linux-foundation.org: fix code layout, per John] [yshigeru@gmail.com: fix uninitialized return value on __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220827230037.78876-1-syoshida@redhat.com Link: https://lkml.kernel.org/r/20220729024645.764366-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-29 10:46:45 +08:00
nr_pinned_pages = __get_user_pages_locked(mm, start, nr_pages,
pages, vmas, locked,
mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. This is indicated by returning zero. When all pages are in the correct zone the number of pinned pages is returned. However migration can also fail, in which case pages are unpinned and -ENOMEM is returned. However if the failure was due to not being unable to isolate a page zero is returned. This leads to indefinite looping in __gup_longterm_locked(). Fix this by simplifying the return codes such that zero indicates all pages were successfully pinned in the correct zone while errors indicate either pages were migrated and pinning should be retried or that migration has failed and therefore the pinning operation should fail. [syoshida@redhat.com: fix return value for __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220821183547.950370-1-syoshida@redhat.com [akpm@linux-foundation.org: fix code layout, per John] [yshigeru@gmail.com: fix uninitialized return value on __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220827230037.78876-1-syoshida@redhat.com Link: https://lkml.kernel.org/r/20220729024645.764366-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-29 10:46:45 +08:00
gup_flags);
if (nr_pinned_pages <= 0) {
rc = nr_pinned_pages;
break;
mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. This is indicated by returning zero. When all pages are in the correct zone the number of pinned pages is returned. However migration can also fail, in which case pages are unpinned and -ENOMEM is returned. However if the failure was due to not being unable to isolate a page zero is returned. This leads to indefinite looping in __gup_longterm_locked(). Fix this by simplifying the return codes such that zero indicates all pages were successfully pinned in the correct zone while errors indicate either pages were migrated and pinning should be retried or that migration has failed and therefore the pinning operation should fail. [syoshida@redhat.com: fix return value for __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220821183547.950370-1-syoshida@redhat.com [akpm@linux-foundation.org: fix code layout, per John] [yshigeru@gmail.com: fix uninitialized return value on __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220827230037.78876-1-syoshida@redhat.com Link: https://lkml.kernel.org/r/20220729024645.764366-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-29 10:46:45 +08:00
}
/* FOLL_LONGTERM implies FOLL_PIN */
rc = check_and_migrate_movable_pages(nr_pinned_pages, pages);
mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. This is indicated by returning zero. When all pages are in the correct zone the number of pinned pages is returned. However migration can also fail, in which case pages are unpinned and -ENOMEM is returned. However if the failure was due to not being unable to isolate a page zero is returned. This leads to indefinite looping in __gup_longterm_locked(). Fix this by simplifying the return codes such that zero indicates all pages were successfully pinned in the correct zone while errors indicate either pages were migrated and pinning should be retried or that migration has failed and therefore the pinning operation should fail. [syoshida@redhat.com: fix return value for __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220821183547.950370-1-syoshida@redhat.com [akpm@linux-foundation.org: fix code layout, per John] [yshigeru@gmail.com: fix uninitialized return value on __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220827230037.78876-1-syoshida@redhat.com Link: https://lkml.kernel.org/r/20220729024645.764366-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-29 10:46:45 +08:00
} while (rc == -EAGAIN);
memalloc_pin_restore(flags);
mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() is called to migrate pages out of zones which should not contain any longterm pinned pages. When migration succeeds all pages will have been unpinned so pinning needs to be retried. This is indicated by returning zero. When all pages are in the correct zone the number of pinned pages is returned. However migration can also fail, in which case pages are unpinned and -ENOMEM is returned. However if the failure was due to not being unable to isolate a page zero is returned. This leads to indefinite looping in __gup_longterm_locked(). Fix this by simplifying the return codes such that zero indicates all pages were successfully pinned in the correct zone while errors indicate either pages were migrated and pinning should be retried or that migration has failed and therefore the pinning operation should fail. [syoshida@redhat.com: fix return value for __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220821183547.950370-1-syoshida@redhat.com [akpm@linux-foundation.org: fix code layout, per John] [yshigeru@gmail.com: fix uninitialized return value on __gup_longterm_locked()] Link: https://lkml.kernel.org/r/20220827230037.78876-1-syoshida@redhat.com Link: https://lkml.kernel.org/r/20220729024645.764366-1-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-29 10:46:45 +08:00
return rc ? rc : nr_pinned_pages;
mm: introduce get_user_pages_longterm Patch series "introduce get_user_pages_longterm()", v2. Here is a new get_user_pages api for cases where a driver intends to keep an elevated page count indefinitely. This is distinct from usages like iov_iter_get_pages where the elevated page counts are transient. The iov_iter_get_pages cases immediately turn around and submit the pages to a device driver which will put_page when the i/o operation completes (under kernel control). In the longterm case userspace is responsible for dropping the page reference at some undefined point in the future. This is untenable for filesystem-dax case where the filesystem is in control of the lifetime of the block / page and needs reasonable limits on how long it can wait for pages in a mapping to become idle. Fixing filesystems to actually wait for dax pages to be idle before blocks from a truncate/hole-punch operation are repurposed is saved for a later patch series. Also, allowing longterm registration of dax mappings is a future patch series that introduces a "map with lease" semantic where the kernel can revoke a lease and force userspace to drop its page references. I have also tagged these for -stable to purposely break cases that might assume that longterm memory registrations for filesystem-dax mappings were supported by the kernel. The behavior regression this policy change implies is one of the reasons we maintain the "dax enabled. Warning: EXPERIMENTAL, use at your own risk" notification when mounting a filesystem in dax mode. It is worth noting the device-dax interface does not suffer the same constraints since it does not support file space management operations like hole-punch. This patch (of 4): Until there is a solution to the dma-to-dax vs truncate problem it is not safe to allow long standing memory registrations against filesytem-dax vmas. Device-dax vmas do not have this problem and are explicitly allowed. This is temporary until a "memory registration with layout-lease" mechanism can be implemented for the affected sub-systems (RDMA and V4L2). [akpm@linux-foundation.org: use kcalloc()] Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Dan Williams <dan.j.williams@intel.com> Suggested-by: Christoph Hellwig <hch@lst.de> Cc: Doug Ledford <dledford@redhat.com> Cc: Hal Rosenstock <hal.rosenstock@gmail.com> Cc: Inki Dae <inki.dae@samsung.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Joonyoung Shim <jy0922.shim@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Sean Hefty <sean.hefty@intel.com> Cc: Seung-Woo Kim <sw0312.kim@samsung.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-30 08:10:35 +08:00
}
mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM Pach series "Add FOLL_LONGTERM to GUP fast and use it". HFI1, qib, and mthca, use get_user_pages_fast() due to its performance advantages. These pages can be held for a significant time. But get_user_pages_fast() does not protect against mapping FS DAX pages. Introduce FOLL_LONGTERM and use this flag in get_user_pages_fast() which retains the performance while also adding the FS DAX checks. XDP has also shown interest in using this functionality.[1] In addition we change get_user_pages() to use the new FOLL_LONGTERM flag and remove the specialized get_user_pages_longterm call. [1] https://lkml.org/lkml/2019/3/19/939 "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Secondly, it depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an aside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. This patch (of 7): This patch starts a series which aims to support FOLL_LONGTERM in get_user_pages_fast(). Some callers who would like to do a longterm (user controlled pin) of pages with the fast variant of GUP for performance purposes. Rather than have a separate get_user_pages_longterm() call, introduce FOLL_LONGTERM and change the longterm callers to use it. This patch does not change any functionality. In the short term "longterm" or user controlled pins are unsafe for Filesystems and FS DAX in particular has been blocked. However, callers of get_user_pages_fast() were not "protected". FOLL_LONGTERM can _only_ be supported with get_user_pages[_fast]() as it requires vmas to determine if DAX is in use. NOTE: In merging with the CMA changes we opt to change the get_user_pages() call in check_and_migrate_cma_pages() to a call of __get_user_pages_locked() on the newly migrated pages. This makes the code read better in that we are calling __get_user_pages_locked() on the pages before and after a potential migration. As a side affect some of the interfaces are cleaned up but this is not the primary purpose of the series. In review[1] it was asked: <quote> > This I don't get - if you do lock down long term mappings performance > of the actual get_user_pages call shouldn't matter to start with. > > What do I miss? A couple of points. First "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Second, It depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an asside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. </quote> [1] https://lore.kernel.org/lkml/20190220180255.GA12020@iweiny-DESK2.sc.intel.com/T/#md6abad2569f3bf6c1f03686c8097ab6563e94965 [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-2-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Rich Felker <dalias@libc.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: James Hogan <jhogan@kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:03 +08:00
/*
* Check that the given flags are valid for the exported gup/pup interface, and
* update them with the required flags that the caller must have set.
*/
static bool is_valid_gup_args(struct page **pages, struct vm_area_struct **vmas,
int *locked, unsigned int *gup_flags_p,
unsigned int to_set)
mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM gup prohibits users from calling get_user_pages() with FOLL_PIN. But it allows users to call get_user_pages() with FOLL_LONGTERM only. It seems insensible. Since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit users from calling get_user_pages() with FOLL_LONGTERM while not with FOLL_PIN. mm/gup_benchmark.c used to be the only user who did this improperly. But it has been fixed by moving to use pin_user_pages(). [akpm@linux-foundation.org: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-14 07:51:58 +08:00
{
unsigned int gup_flags = *gup_flags_p;
mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM gup prohibits users from calling get_user_pages() with FOLL_PIN. But it allows users to call get_user_pages() with FOLL_LONGTERM only. It seems insensible. Since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit users from calling get_user_pages() with FOLL_LONGTERM while not with FOLL_PIN. mm/gup_benchmark.c used to be the only user who did this improperly. But it has been fixed by moving to use pin_user_pages(). [akpm@linux-foundation.org: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-14 07:51:58 +08:00
/*
* These flags not allowed to be specified externally to the gup
* interfaces:
* - FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
* - FOLL_REMOTE is internal only and used on follow_page()
* - FOLL_UNLOCKABLE is internal only and used if locked is !NULL
mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM gup prohibits users from calling get_user_pages() with FOLL_PIN. But it allows users to call get_user_pages() with FOLL_LONGTERM only. It seems insensible. Since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit users from calling get_user_pages() with FOLL_LONGTERM while not with FOLL_PIN. mm/gup_benchmark.c used to be the only user who did this improperly. But it has been fixed by moving to use pin_user_pages(). [akpm@linux-foundation.org: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-14 07:51:58 +08:00
*/
if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_TRIED | FOLL_UNLOCKABLE |
FOLL_REMOTE | FOLL_FAST_ONLY)))
return false;
gup_flags |= to_set;
if (locked) {
/* At the external interface locked must be set */
if (WARN_ON_ONCE(*locked != 1))
return false;
gup_flags |= FOLL_UNLOCKABLE;
}
/* FOLL_GET and FOLL_PIN are mutually exclusive. */
if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
(FOLL_PIN | FOLL_GET)))
return false;
/* LONGTERM can only be specified when pinning */
if (WARN_ON_ONCE(!(gup_flags & FOLL_PIN) && (gup_flags & FOLL_LONGTERM)))
return false;
/* Pages input must be given if using GET/PIN */
if (WARN_ON_ONCE((gup_flags & (FOLL_GET | FOLL_PIN)) && !pages))
mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM gup prohibits users from calling get_user_pages() with FOLL_PIN. But it allows users to call get_user_pages() with FOLL_LONGTERM only. It seems insensible. Since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit users from calling get_user_pages() with FOLL_LONGTERM while not with FOLL_PIN. mm/gup_benchmark.c used to be the only user who did this improperly. But it has been fixed by moving to use pin_user_pages(). [akpm@linux-foundation.org: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-14 07:51:58 +08:00
return false;
/* We want to allow the pgmap to be hot-unplugged at all times */
if (WARN_ON_ONCE((gup_flags & FOLL_LONGTERM) &&
(gup_flags & FOLL_PCI_P2PDMA)))
return false;
mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM gup prohibits users from calling get_user_pages() with FOLL_PIN. But it allows users to call get_user_pages() with FOLL_LONGTERM only. It seems insensible. Since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit users from calling get_user_pages() with FOLL_LONGTERM while not with FOLL_PIN. mm/gup_benchmark.c used to be the only user who did this improperly. But it has been fixed by moving to use pin_user_pages(). [akpm@linux-foundation.org: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-14 07:51:58 +08:00
/*
* Can't use VMAs with locked, as locked allows GUP to unlock
* which invalidates the vmas array
mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM gup prohibits users from calling get_user_pages() with FOLL_PIN. But it allows users to call get_user_pages() with FOLL_LONGTERM only. It seems insensible. Since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit users from calling get_user_pages() with FOLL_LONGTERM while not with FOLL_PIN. mm/gup_benchmark.c used to be the only user who did this improperly. But it has been fixed by moving to use pin_user_pages(). [akpm@linux-foundation.org: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-14 07:51:58 +08:00
*/
if (WARN_ON_ONCE(vmas && (gup_flags & FOLL_UNLOCKABLE)))
mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM gup prohibits users from calling get_user_pages() with FOLL_PIN. But it allows users to call get_user_pages() with FOLL_LONGTERM only. It seems insensible. Since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit users from calling get_user_pages() with FOLL_LONGTERM while not with FOLL_PIN. mm/gup_benchmark.c used to be the only user who did this improperly. But it has been fixed by moving to use pin_user_pages(). [akpm@linux-foundation.org: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-14 07:51:58 +08:00
return false;
*gup_flags_p = gup_flags;
mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM gup prohibits users from calling get_user_pages() with FOLL_PIN. But it allows users to call get_user_pages() with FOLL_LONGTERM only. It seems insensible. Since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit users from calling get_user_pages() with FOLL_LONGTERM while not with FOLL_PIN. mm/gup_benchmark.c used to be the only user who did this improperly. But it has been fixed by moving to use pin_user_pages(). [akpm@linux-foundation.org: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Naresh Kamboju <naresh.kamboju@linaro.org> Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-14 07:51:58 +08:00
return true;
}
mm/gup: split get_user_pages_remote() into two routines Patch series "mm/gup: track FOLL_PIN pages", v6. This activates tracking of FOLL_PIN pages. This is in support of fixing the get_user_pages()+DMA problem described in [1]-[4]. FOLL_PIN support is now in the main linux tree. However, the patch to use FOLL_PIN to track pages was *not* submitted, because Leon saw an RDMA test suite failure that involved (I think) page refcount overflows when huge pages were used. This patch definitively solves that kind of overflow problem, by adding an exact pincount, for compound pages (of order > 1), in the 3rd struct page of a compound page. If available, that form of pincounting is used, instead of the GUP_PIN_COUNTING_BIAS approach. Thanks again to Jan Kara for that idea. Other interesting changes: * dump_page(): added one, or two new things to report for compound pages: head refcount (for all compound pages), and map_pincount (for compound pages of order > 1). * Documentation/core-api/pin_user_pages.rst: removed the "TODO" for the huge page refcount upper limit problems, and added notes about how it works now. Also added a note about the dump_page() enhancements. * Added some comments in gup.c and mm.h, to explain that there are two ways to count pinned pages: exact (for compound pages of order > 1) and fuzzy (GUP_PIN_COUNTING_BIAS: for all other pages). ============================================================ General notes about the tracking patch: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], [4] and in a remarkable number of email threads since about 2017. :) In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() ============================================================ Future steps: * Convert more subsystems from get_user_pages() to pin_user_pages(). The first probably needs to be bio/biovecs, because any filesystem testing is too difficult without those in place. * Change VFS and filesystems to respond appropriately when encountering dma-pinned pages. * Work with Ira and others to connect this all up with file system leases. [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages() https://lwn.net/Kernel/Index/#Memory_management-get_user_pages This patch (of 12): An upcoming patch requires reusing the implementation of get_user_pages_remote(). Split up get_user_pages_remote() into an outer routine that checks flags, and an implementation routine that will be reused. This makes subsequent changes much easier to understand. There should be no change in behavior due to this patch. Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-2-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:10 +08:00
#ifdef CONFIG_MMU
/**
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
* get_user_pages_remote() - pin user pages in memory
* @mm: mm_struct of target mm
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying lookup behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long. Or NULL, if caller
* only intends to ensure the pages are faulted in.
* @vmas: array of pointers to vmas corresponding to each page.
* Or NULL if the caller does not require them.
* @locked: pointer to lock flag indicating whether lock is held and
* subsequently whether VM_FAULT_RETRY functionality can be
* utilised. Lock must initially be held.
*
* Returns either number of pages pinned (which may be less than the
* number requested), or an error. Details about the return value:
*
* -- If nr_pages is 0, returns 0.
* -- If nr_pages is >0, but no pages were pinned, returns -errno.
* -- If nr_pages is >0, and some pages were pinned, returns the number of
* pages pinned. Again, this may be less than nr_pages.
*
* The caller is responsible for releasing returned @pages, via put_page().
*
* @vmas are valid only as long as mmap_lock is held.
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
*
* Must be called with mmap_lock held for read or write.
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
*
* get_user_pages_remote walks a process's page tables and takes a reference
* to each struct page that each user address corresponds to at a given
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
* instant. That is, it takes the page that would be accessed if a user
* thread accesses the given user virtual address at that instant.
*
* This does not guarantee that the page exists in the user mappings when
* get_user_pages_remote returns, and there may even be a completely different
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
* page there in some cases (eg. if mmapped pagecache has been invalidated
* and subsequently re-faulted). However it does guarantee that the page
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
* won't be freed completely. And mostly callers simply care that the page
* contains data that was valid *at some point in time*. Typically, an IO
* or similar operation cannot guarantee anything stronger anyway because
* locks can't be held over the syscall boundary.
*
* If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
* is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
* be called after the page is finished with, and before put_page is called.
*
* get_user_pages_remote is typically used for fewer-copy IO operations,
* to get a handle on the memory by some means other than accesses
* via the user virtual addresses. The pages may be submitted for
* DMA to devices or accessed via their kernel linear mapping (via the
* kmap APIs). Care should be taken to use the correct cache flushing APIs.
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
*
* See also get_user_pages_fast, for performance critical applications.
*
* get_user_pages_remote should be phased out in favor of
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
* get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
* should use get_user_pages_remote because it cannot pass
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
* FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
*/
long get_user_pages_remote(struct mm_struct *mm,
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas, int *locked)
{
int local_locked = 1;
if (!is_valid_gup_args(pages, vmas, locked, &gup_flags,
FOLL_TOUCH | FOLL_REMOTE))
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
return -EINVAL;
return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
locked ? locked : &local_locked,
gup_flags);
mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments to loosen the restriction, allowing FOLL_LONGTERM in some cases. Also, copy the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). This check will then be removed from the VFIO call site in a subsequent patch. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Link: http://lkml.kernel.org/r/20200107224558.2362728-7-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jan Kara <jack@suse.cz> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:36 +08:00
}
EXPORT_SYMBOL(get_user_pages_remote);
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
#else /* CONFIG_MMU */
long get_user_pages_remote(struct mm_struct *mm,
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas, int *locked)
{
return 0;
}
#endif /* !CONFIG_MMU */
/**
* get_user_pages() - pin user pages in memory
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying lookup behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long. Or NULL, if caller
* only intends to ensure the pages are faulted in.
* @vmas: array of pointers to vmas corresponding to each page.
* Or NULL if the caller does not require them.
*
* This is the same as get_user_pages_remote(), just with a less-flexible
* calling convention where we assume that the mm being operated on belongs to
* the current task, and doesn't allow passing of a locked parameter. We also
* obviously don't pass FOLL_REMOTE in here.
mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM Pach series "Add FOLL_LONGTERM to GUP fast and use it". HFI1, qib, and mthca, use get_user_pages_fast() due to its performance advantages. These pages can be held for a significant time. But get_user_pages_fast() does not protect against mapping FS DAX pages. Introduce FOLL_LONGTERM and use this flag in get_user_pages_fast() which retains the performance while also adding the FS DAX checks. XDP has also shown interest in using this functionality.[1] In addition we change get_user_pages() to use the new FOLL_LONGTERM flag and remove the specialized get_user_pages_longterm call. [1] https://lkml.org/lkml/2019/3/19/939 "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Secondly, it depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an aside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. This patch (of 7): This patch starts a series which aims to support FOLL_LONGTERM in get_user_pages_fast(). Some callers who would like to do a longterm (user controlled pin) of pages with the fast variant of GUP for performance purposes. Rather than have a separate get_user_pages_longterm() call, introduce FOLL_LONGTERM and change the longterm callers to use it. This patch does not change any functionality. In the short term "longterm" or user controlled pins are unsafe for Filesystems and FS DAX in particular has been blocked. However, callers of get_user_pages_fast() were not "protected". FOLL_LONGTERM can _only_ be supported with get_user_pages[_fast]() as it requires vmas to determine if DAX is in use. NOTE: In merging with the CMA changes we opt to change the get_user_pages() call in check_and_migrate_cma_pages() to a call of __get_user_pages_locked() on the newly migrated pages. This makes the code read better in that we are calling __get_user_pages_locked() on the pages before and after a potential migration. As a side affect some of the interfaces are cleaned up but this is not the primary purpose of the series. In review[1] it was asked: <quote> > This I don't get - if you do lock down long term mappings performance > of the actual get_user_pages call shouldn't matter to start with. > > What do I miss? A couple of points. First "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Second, It depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an asside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. </quote> [1] https://lore.kernel.org/lkml/20190220180255.GA12020@iweiny-DESK2.sc.intel.com/T/#md6abad2569f3bf6c1f03686c8097ab6563e94965 [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-2-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Rich Felker <dalias@libc.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: James Hogan <jhogan@kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:03 +08:00
*/
long get_user_pages(unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas)
{
int locked = 1;
if (!is_valid_gup_args(pages, vmas, NULL, &gup_flags, FOLL_TOUCH))
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
return -EINVAL;
return __get_user_pages_locked(current->mm, start, nr_pages, pages,
vmas, &locked, gup_flags);
mm/gup: replace get_user_pages_longterm() with FOLL_LONGTERM Pach series "Add FOLL_LONGTERM to GUP fast and use it". HFI1, qib, and mthca, use get_user_pages_fast() due to its performance advantages. These pages can be held for a significant time. But get_user_pages_fast() does not protect against mapping FS DAX pages. Introduce FOLL_LONGTERM and use this flag in get_user_pages_fast() which retains the performance while also adding the FS DAX checks. XDP has also shown interest in using this functionality.[1] In addition we change get_user_pages() to use the new FOLL_LONGTERM flag and remove the specialized get_user_pages_longterm call. [1] https://lkml.org/lkml/2019/3/19/939 "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Secondly, it depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an aside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. This patch (of 7): This patch starts a series which aims to support FOLL_LONGTERM in get_user_pages_fast(). Some callers who would like to do a longterm (user controlled pin) of pages with the fast variant of GUP for performance purposes. Rather than have a separate get_user_pages_longterm() call, introduce FOLL_LONGTERM and change the longterm callers to use it. This patch does not change any functionality. In the short term "longterm" or user controlled pins are unsafe for Filesystems and FS DAX in particular has been blocked. However, callers of get_user_pages_fast() were not "protected". FOLL_LONGTERM can _only_ be supported with get_user_pages[_fast]() as it requires vmas to determine if DAX is in use. NOTE: In merging with the CMA changes we opt to change the get_user_pages() call in check_and_migrate_cma_pages() to a call of __get_user_pages_locked() on the newly migrated pages. This makes the code read better in that we are calling __get_user_pages_locked() on the pages before and after a potential migration. As a side affect some of the interfaces are cleaned up but this is not the primary purpose of the series. In review[1] it was asked: <quote> > This I don't get - if you do lock down long term mappings performance > of the actual get_user_pages call shouldn't matter to start with. > > What do I miss? A couple of points. First "longterm" is a relative thing and at this point is probably a misnomer. This is really flagging a pin which is going to be given to hardware and can't move. I've thought of a couple of alternative names but I think we have to settle on if we are going to use FL_LAYOUT or something else to solve the "longterm" problem. Then I think we can change the flag to a better name. Second, It depends on how often you are registering memory. I have spoken with some RDMA users who consider MR in the performance path... For the overall application performance. I don't have the numbers as the tests for HFI1 were done a long time ago. But there was a significant advantage. Some of which is probably due to the fact that you don't have to hold mmap_sem. Finally, architecturally I think it would be good for everyone to use *_fast. There are patches submitted to the RDMA list which would allow the use of *_fast (they reworking the use of mmap_sem) and as soon as they are accepted I'll submit a patch to convert the RDMA core as well. Also to this point others are looking to use *_fast. As an asside, Jasons pointed out in my previous submission that *_fast and *_unlocked look very much the same. I agree and I think further cleanup will be coming. But I'm focused on getting the final solution for DAX at the moment. </quote> [1] https://lore.kernel.org/lkml/20190220180255.GA12020@iweiny-DESK2.sc.intel.com/T/#md6abad2569f3bf6c1f03686c8097ab6563e94965 [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-2-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Rich Felker <dalias@libc.org> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: James Hogan <jhogan@kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:03 +08:00
}
EXPORT_SYMBOL(get_user_pages);
mm: introduce get_user_pages_longterm Patch series "introduce get_user_pages_longterm()", v2. Here is a new get_user_pages api for cases where a driver intends to keep an elevated page count indefinitely. This is distinct from usages like iov_iter_get_pages where the elevated page counts are transient. The iov_iter_get_pages cases immediately turn around and submit the pages to a device driver which will put_page when the i/o operation completes (under kernel control). In the longterm case userspace is responsible for dropping the page reference at some undefined point in the future. This is untenable for filesystem-dax case where the filesystem is in control of the lifetime of the block / page and needs reasonable limits on how long it can wait for pages in a mapping to become idle. Fixing filesystems to actually wait for dax pages to be idle before blocks from a truncate/hole-punch operation are repurposed is saved for a later patch series. Also, allowing longterm registration of dax mappings is a future patch series that introduces a "map with lease" semantic where the kernel can revoke a lease and force userspace to drop its page references. I have also tagged these for -stable to purposely break cases that might assume that longterm memory registrations for filesystem-dax mappings were supported by the kernel. The behavior regression this policy change implies is one of the reasons we maintain the "dax enabled. Warning: EXPERIMENTAL, use at your own risk" notification when mounting a filesystem in dax mode. It is worth noting the device-dax interface does not suffer the same constraints since it does not support file space management operations like hole-punch. This patch (of 4): Until there is a solution to the dma-to-dax vs truncate problem it is not safe to allow long standing memory registrations against filesytem-dax vmas. Device-dax vmas do not have this problem and are explicitly allowed. This is temporary until a "memory registration with layout-lease" mechanism can be implemented for the affected sub-systems (RDMA and V4L2). [akpm@linux-foundation.org: use kcalloc()] Link: http://lkml.kernel.org/r/151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Dan Williams <dan.j.williams@intel.com> Suggested-by: Christoph Hellwig <hch@lst.de> Cc: Doug Ledford <dledford@redhat.com> Cc: Hal Rosenstock <hal.rosenstock@gmail.com> Cc: Inki Dae <inki.dae@samsung.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Joonyoung Shim <jy0922.shim@samsung.com> Cc: Kyungmin Park <kyungmin.park@samsung.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Sean Hefty <sean.hefty@intel.com> Cc: Seung-Woo Kim <sw0312.kim@samsung.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-30 08:10:35 +08:00
/*
* get_user_pages_unlocked() is suitable to replace the form:
*
* mmap_read_lock(mm);
* get_user_pages(mm, ..., pages, NULL);
* mmap_read_unlock(mm);
*
* with:
*
* get_user_pages_unlocked(mm, ..., pages);
*
* It is functionally equivalent to get_user_pages_fast so
* get_user_pages_fast should be used instead if specific gup_flags
* (e.g. FOLL_FORCE) are not required.
*/
long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
struct page **pages, unsigned int gup_flags)
{
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
int locked = 0;
if (!is_valid_gup_args(pages, NULL, NULL, &gup_flags,
FOLL_TOUCH | FOLL_UNLOCKABLE))
return -EINVAL;
return __get_user_pages_locked(current->mm, start, nr_pages, pages,
NULL, &locked, gup_flags);
}
EXPORT_SYMBOL(get_user_pages_unlocked);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
/*
* Fast GUP
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
*
* get_user_pages_fast attempts to pin user pages by walking the page
* tables directly and avoids taking locks. Thus the walker needs to be
* protected from page table pages being freed from under it, and should
* block any THP splits.
*
* One way to achieve this is to have the walker disable interrupts, and
* rely on IPIs from the TLB flushing code blocking before the page table
* pages are freed. This is unsuitable for architectures that do not need
* to broadcast an IPI when invalidating TLBs.
*
* Another way to achieve this is to batch up page table containing pages
* belonging to more than one mm_user, then rcu_sched a callback to free those
* pages. Disabling interrupts will allow the fast_gup walker to both block
* the rcu_sched callback, and an IPI that we broadcast for splitting THPs
* (which is a relatively rare event). The code below adopts this strategy.
*
* Before activating this code, please be aware that the following assumptions
* are currently made:
*
* *) Either MMU_GATHER_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
* free pages containing page tables or TLB flushing requires IPI broadcast.
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
*
* *) ptes can be read atomically by the architecture.
*
* *) access_ok is sufficient to validate userspace address ranges.
*
* The last two assumptions can be relaxed by the addition of helper functions.
*
* This code is based heavily on the PowerPC implementation by Nick Piggin.
*/
#ifdef CONFIG_HAVE_FAST_GUP
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
unsigned int flags,
struct page **pages)
{
while ((*nr) - nr_start) {
struct page *page = pages[--(*nr)];
ClearPageReferenced(page);
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
if (flags & FOLL_PIN)
unpin_user_page(page);
else
put_page(page);
}
}
mm: introduce ARCH_HAS_PTE_SPECIAL Currently the PTE special supports is turned on in per architecture header files. Most of the time, it is defined in arch/*/include/asm/pgtable.h depending or not on some other per architecture static definition. This patch introduce a new configuration variable to manage this directly in the Kconfig files. It would later replace __HAVE_ARCH_PTE_SPECIAL. Here notes for some architecture where the definition of __HAVE_ARCH_PTE_SPECIAL is not obvious: arm __HAVE_ARCH_PTE_SPECIAL which is currently defined in arch/arm/include/asm/pgtable-3level.h which is included by arch/arm/include/asm/pgtable.h when CONFIG_ARM_LPAE is set. So select ARCH_HAS_PTE_SPECIAL if ARM_LPAE. powerpc __HAVE_ARCH_PTE_SPECIAL is defined in 2 files: - arch/powerpc/include/asm/book3s/64/pgtable.h - arch/powerpc/include/asm/pte-common.h The first one is included if (PPC_BOOK3S & PPC64) while the second is included in all the other cases. So select ARCH_HAS_PTE_SPECIAL all the time. sparc: __HAVE_ARCH_PTE_SPECIAL is defined if defined(__sparc__) && defined(__arch64__) which are defined through the compiler in sparc/Makefile if !SPARC32 which I assume to be if SPARC64. So select ARCH_HAS_PTE_SPECIAL if SPARC64 There is no functional change introduced by this patch. Link: http://lkml.kernel.org/r/1523433816-14460-2-git-send-email-ldufour@linux.vnet.ibm.com Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com> Suggested-by: Jerome Glisse <jglisse@redhat.com> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Acked-by: David Rientjes <rientjes@google.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Rich Felker <dalias@libc.org> Cc: David S. Miller <davem@davemloft.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Vineet Gupta <vgupta@synopsys.com> Cc: Palmer Dabbelt <palmer@sifive.com> Cc: Albert Ou <albert@sifive.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Robin Murphy <robin.murphy@arm.com> Cc: Christophe LEROY <christophe.leroy@c-s.fr> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-06-08 08:06:08 +08:00
#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
mm: gup: fix the fast GUP race against THP collapse Since general RCU GUP fast was introduced in commit 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()"), a TLB flush is no longer sufficient to handle concurrent GUP-fast in all cases, it only handles traditional IPI-based GUP-fast correctly. On architectures that send an IPI broadcast on TLB flush, it works as expected. But on the architectures that do not use IPI to broadcast TLB flush, it may have the below race: CPU A CPU B THP collapse fast GUP gup_pmd_range() <-- see valid pmd gup_pte_range() <-- work on pte pmdp_collapse_flush() <-- clear pmd and flush __collapse_huge_page_isolate() check page pinned <-- before GUP bump refcount pin the page check PTE <-- no change __collapse_huge_page_copy() copy data to huge page ptep_clear() install huge pmd for the huge page return the stale page discard the stale page The race can be fixed by checking whether PMD is changed or not after taking the page pin in fast GUP, just like what it does for PTE. If the PMD is changed it means there may be parallel THP collapse, so GUP should back off. Also update the stale comment about serializing against fast GUP in khugepaged. Link: https://lkml.kernel.org/r/20220907180144.555485-1-shy828301@gmail.com Fixes: 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()") Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Peter Xu <peterx@redhat.com> Signed-off-by: Yang Shi <shy828301@gmail.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-09-08 02:01:43 +08:00
/*
* Fast-gup relies on pte change detection to avoid concurrent pgtable
* operations.
*
* To pin the page, fast-gup needs to do below in order:
* (1) pin the page (by prefetching pte), then (2) check pte not changed.
*
* For the rest of pgtable operations where pgtable updates can be racy
* with fast-gup, we need to do (1) clear pte, then (2) check whether page
* is pinned.
*
* Above will work for all pte-level operations, including THP split.
*
* For THP collapse, it's a bit more complicated because fast-gup may be
* walking a pgtable page that is being freed (pte is still valid but pmd
* can be cleared already). To avoid race in such condition, we need to
* also check pmd here to make sure pmd doesn't change (corresponds to
* pmdp_collapse_flush() in the THP collapse code path).
*/
static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
{
struct dev_pagemap *pgmap = NULL;
int nr_start = *nr, ret = 0;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
pte_t *ptep, *ptem;
ptem = ptep = pte_offset_map(&pmd, addr);
do {
pte_t pte = ptep_get_lockless(ptep);
struct page *page;
struct folio *folio;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
if (pte_protnone(pte) && !gup_can_follow_protnone(flags))
goto pte_unmap;
if (!pte_access_permitted(pte, flags & FOLL_WRITE))
goto pte_unmap;
if (pte_devmap(pte)) {
mm/gup: add FOLL_LONGTERM capability to GUP fast DAX pages were previously unprotected from longterm pins when users called get_user_pages_fast(). Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall back to regular GUP processing if a DEVMAP page is encountered. [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-5-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Hogan <jhogan@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Rich Felker <dalias@libc.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:14 +08:00
if (unlikely(flags & FOLL_LONGTERM))
goto pte_unmap;
pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
if (unlikely(!pgmap)) {
undo_dev_pagemap(nr, nr_start, flags, pages);
goto pte_unmap;
}
} else if (pte_special(pte))
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
goto pte_unmap;
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
folio = try_grab_folio(page, 1, flags);
if (!folio)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
goto pte_unmap;
mm: introduce memfd_secret system call to create "secret" memory areas Introduce "memfd_secret" system call with the ability to create memory areas visible only in the context of the owning process and not mapped not only to other processes but in the kernel page tables as well. The secretmem feature is off by default and the user must explicitly enable it at the boot time. Once secretmem is enabled, the user will be able to create a file descriptor using the memfd_secret() system call. The memory areas created by mmap() calls from this file descriptor will be unmapped from the kernel direct map and they will be only mapped in the page table of the processes that have access to the file descriptor. Secretmem is designed to provide the following protections: * Enhanced protection (in conjunction with all the other in-kernel attack prevention systems) against ROP attacks. Seceretmem makes "simple" ROP insufficient to perform exfiltration, which increases the required complexity of the attack. Along with other protections like the kernel stack size limit and address space layout randomization which make finding gadgets is really hard, absence of any in-kernel primitive for accessing secret memory means the one gadget ROP attack can't work. Since the only way to access secret memory is to reconstruct the missing mapping entry, the attacker has to recover the physical page and insert a PTE pointing to it in the kernel and then retrieve the contents. That takes at least three gadgets which is a level of difficulty beyond most standard attacks. * Prevent cross-process secret userspace memory exposures. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere. The secreremem pages cannot be accessed via the direct map and they are disallowed in GUP. * Harden against exploited kernel flaws. In order to access secretmem, a kernel-side attack would need to either walk the page tables and create new ones, or spawn a new privileged uiserspace process to perform secrets exfiltration using ptrace. The file descriptor based memory has several advantages over the "traditional" mm interfaces, such as mlock(), mprotect(), madvise(). File descriptor approach allows explicit and controlled sharing of the memory areas, it allows to seal the operations. Besides, file descriptor based memory paves the way for VMMs to remove the secret memory range from the userspace hipervisor process, for instance QEMU. Andy Lutomirski says: "Getting fd-backed memory into a guest will take some possibly major work in the kernel, but getting vma-backed memory into a guest without mapping it in the host user address space seems much, much worse." memfd_secret() is made a dedicated system call rather than an extension to memfd_create() because it's purpose is to allow the user to create more secure memory mappings rather than to simply allow file based access to the memory. Nowadays a new system call cost is negligible while it is way simpler for userspace to deal with a clear-cut system calls than with a multiplexer or an overloaded syscall. Moreover, the initial implementation of memfd_secret() is completely distinct from memfd_create() so there is no much sense in overloading memfd_create() to begin with. If there will be a need for code sharing between these implementation it can be easily achieved without a need to adjust user visible APIs. The secret memory remains accessible in the process context using uaccess primitives, but it is not exposed to the kernel otherwise; secret memory areas are removed from the direct map and functions in the follow_page()/get_user_page() family will refuse to return a page that belongs to the secret memory area. Once there will be a use case that will require exposing secretmem to the kernel it will be an opt-in request in the system call flags so that user would have to decide what data can be exposed to the kernel. Removing of the pages from the direct map may cause its fragmentation on architectures that use large pages to map the physical memory which affects the system performance. However, the original Kconfig text for CONFIG_DIRECT_GBPAGES said that gigabyte pages in the direct map "... can improve the kernel's performance a tiny bit ..." (commit 00d1c5e05736 ("x86: add gbpages switches")) and the recent report [1] showed that "... although 1G mappings are a good default choice, there is no compelling evidence that it must be the only choice". Hence, it is sufficient to have secretmem disabled by default with the ability of a system administrator to enable it at boot time. Pages in the secretmem regions are unevictable and unmovable to avoid accidental exposure of the sensitive data via swap or during page migration. Since the secretmem mappings are locked in memory they cannot exceed RLIMIT_MEMLOCK. Since these mappings are already locked independently from mlock(), an attempt to mlock()/munlock() secretmem range would fail and mlockall()/munlockall() will ignore secretmem mappings. However, unlike mlock()ed memory, secretmem currently behaves more like long-term GUP: secretmem mappings are unmovable mappings directly consumed by user space. With default limits, there is no excessive use of secretmem and it poses no real problem in combination with ZONE_MOVABLE/CMA, but in the future this should be addressed to allow balanced use of large amounts of secretmem along with ZONE_MOVABLE/CMA. A page that was a part of the secret memory area is cleared when it is freed to ensure the data is not exposed to the next user of that page. The following example demonstrates creation of a secret mapping (error handling is omitted): fd = memfd_secret(0); ftruncate(fd, MAP_SIZE); ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); [1] https://lore.kernel.org/linux-mm/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux.intel.com/ [akpm@linux-foundation.org: suppress Kconfig whine] Link: https://lkml.kernel.org/r/20210518072034.31572-5-rppt@kernel.org Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: Hagen Paul Pfeifer <hagen@jauu.net> Acked-by: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christopher Lameter <cl@linux.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Bottomley <jejb@linux.ibm.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Palmer Dabbelt <palmerdabbelt@google.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tycho Andersen <tycho@tycho.ws> Cc: Will Deacon <will@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: kernel test robot <lkp@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-08 09:08:03 +08:00
if (unlikely(page_is_secretmem(page))) {
gup_put_folio(folio, 1, flags);
mm: introduce memfd_secret system call to create "secret" memory areas Introduce "memfd_secret" system call with the ability to create memory areas visible only in the context of the owning process and not mapped not only to other processes but in the kernel page tables as well. The secretmem feature is off by default and the user must explicitly enable it at the boot time. Once secretmem is enabled, the user will be able to create a file descriptor using the memfd_secret() system call. The memory areas created by mmap() calls from this file descriptor will be unmapped from the kernel direct map and they will be only mapped in the page table of the processes that have access to the file descriptor. Secretmem is designed to provide the following protections: * Enhanced protection (in conjunction with all the other in-kernel attack prevention systems) against ROP attacks. Seceretmem makes "simple" ROP insufficient to perform exfiltration, which increases the required complexity of the attack. Along with other protections like the kernel stack size limit and address space layout randomization which make finding gadgets is really hard, absence of any in-kernel primitive for accessing secret memory means the one gadget ROP attack can't work. Since the only way to access secret memory is to reconstruct the missing mapping entry, the attacker has to recover the physical page and insert a PTE pointing to it in the kernel and then retrieve the contents. That takes at least three gadgets which is a level of difficulty beyond most standard attacks. * Prevent cross-process secret userspace memory exposures. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere. The secreremem pages cannot be accessed via the direct map and they are disallowed in GUP. * Harden against exploited kernel flaws. In order to access secretmem, a kernel-side attack would need to either walk the page tables and create new ones, or spawn a new privileged uiserspace process to perform secrets exfiltration using ptrace. The file descriptor based memory has several advantages over the "traditional" mm interfaces, such as mlock(), mprotect(), madvise(). File descriptor approach allows explicit and controlled sharing of the memory areas, it allows to seal the operations. Besides, file descriptor based memory paves the way for VMMs to remove the secret memory range from the userspace hipervisor process, for instance QEMU. Andy Lutomirski says: "Getting fd-backed memory into a guest will take some possibly major work in the kernel, but getting vma-backed memory into a guest without mapping it in the host user address space seems much, much worse." memfd_secret() is made a dedicated system call rather than an extension to memfd_create() because it's purpose is to allow the user to create more secure memory mappings rather than to simply allow file based access to the memory. Nowadays a new system call cost is negligible while it is way simpler for userspace to deal with a clear-cut system calls than with a multiplexer or an overloaded syscall. Moreover, the initial implementation of memfd_secret() is completely distinct from memfd_create() so there is no much sense in overloading memfd_create() to begin with. If there will be a need for code sharing between these implementation it can be easily achieved without a need to adjust user visible APIs. The secret memory remains accessible in the process context using uaccess primitives, but it is not exposed to the kernel otherwise; secret memory areas are removed from the direct map and functions in the follow_page()/get_user_page() family will refuse to return a page that belongs to the secret memory area. Once there will be a use case that will require exposing secretmem to the kernel it will be an opt-in request in the system call flags so that user would have to decide what data can be exposed to the kernel. Removing of the pages from the direct map may cause its fragmentation on architectures that use large pages to map the physical memory which affects the system performance. However, the original Kconfig text for CONFIG_DIRECT_GBPAGES said that gigabyte pages in the direct map "... can improve the kernel's performance a tiny bit ..." (commit 00d1c5e05736 ("x86: add gbpages switches")) and the recent report [1] showed that "... although 1G mappings are a good default choice, there is no compelling evidence that it must be the only choice". Hence, it is sufficient to have secretmem disabled by default with the ability of a system administrator to enable it at boot time. Pages in the secretmem regions are unevictable and unmovable to avoid accidental exposure of the sensitive data via swap or during page migration. Since the secretmem mappings are locked in memory they cannot exceed RLIMIT_MEMLOCK. Since these mappings are already locked independently from mlock(), an attempt to mlock()/munlock() secretmem range would fail and mlockall()/munlockall() will ignore secretmem mappings. However, unlike mlock()ed memory, secretmem currently behaves more like long-term GUP: secretmem mappings are unmovable mappings directly consumed by user space. With default limits, there is no excessive use of secretmem and it poses no real problem in combination with ZONE_MOVABLE/CMA, but in the future this should be addressed to allow balanced use of large amounts of secretmem along with ZONE_MOVABLE/CMA. A page that was a part of the secret memory area is cleared when it is freed to ensure the data is not exposed to the next user of that page. The following example demonstrates creation of a secret mapping (error handling is omitted): fd = memfd_secret(0); ftruncate(fd, MAP_SIZE); ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); [1] https://lore.kernel.org/linux-mm/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux.intel.com/ [akpm@linux-foundation.org: suppress Kconfig whine] Link: https://lkml.kernel.org/r/20210518072034.31572-5-rppt@kernel.org Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: Hagen Paul Pfeifer <hagen@jauu.net> Acked-by: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christopher Lameter <cl@linux.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Bottomley <jejb@linux.ibm.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Palmer Dabbelt <palmerdabbelt@google.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tycho Andersen <tycho@tycho.ws> Cc: Will Deacon <will@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: kernel test robot <lkp@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-08 09:08:03 +08:00
goto pte_unmap;
}
mm: gup: fix the fast GUP race against THP collapse Since general RCU GUP fast was introduced in commit 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()"), a TLB flush is no longer sufficient to handle concurrent GUP-fast in all cases, it only handles traditional IPI-based GUP-fast correctly. On architectures that send an IPI broadcast on TLB flush, it works as expected. But on the architectures that do not use IPI to broadcast TLB flush, it may have the below race: CPU A CPU B THP collapse fast GUP gup_pmd_range() <-- see valid pmd gup_pte_range() <-- work on pte pmdp_collapse_flush() <-- clear pmd and flush __collapse_huge_page_isolate() check page pinned <-- before GUP bump refcount pin the page check PTE <-- no change __collapse_huge_page_copy() copy data to huge page ptep_clear() install huge pmd for the huge page return the stale page discard the stale page The race can be fixed by checking whether PMD is changed or not after taking the page pin in fast GUP, just like what it does for PTE. If the PMD is changed it means there may be parallel THP collapse, so GUP should back off. Also update the stale comment about serializing against fast GUP in khugepaged. Link: https://lkml.kernel.org/r/20220907180144.555485-1-shy828301@gmail.com Fixes: 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()") Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Peter Xu <peterx@redhat.com> Signed-off-by: Yang Shi <shy828301@gmail.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-09-08 02:01:43 +08:00
if (unlikely(pmd_val(pmd) != pmd_val(*pmdp)) ||
unlikely(pte_val(pte) != pte_val(*ptep))) {
gup_put_folio(folio, 1, flags);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
goto pte_unmap;
}
mm/gup: reliable R/O long-term pinning in COW mappings We already support reliable R/O pinning of anonymous memory. However, assume we end up pinning (R/O long-term) a pagecache page or the shared zeropage inside a writable private ("COW") mapping. The next write access will trigger a write-fault and replace the pinned page by an exclusive anonymous page in the process page tables to break COW: the pinned page no longer corresponds to the page mapped into the process' page table. Now that FAULT_FLAG_UNSHARE can break COW on anything mapped into a COW mapping, let's properly break COW first before R/O long-term pinning something that's not an exclusive anon page inside a COW mapping. FAULT_FLAG_UNSHARE will break COW and map an exclusive anon page instead that can get pinned safely. With this change, we can stop using FOLL_FORCE|FOLL_WRITE for reliable R/O long-term pinning in COW mappings. With this change, the new R/O long-term pinning tests for non-anonymous memory succeed: # [RUN] R/O longterm GUP pin ... with shared zeropage ok 151 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd ok 152 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with tmpfile ok 153 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with huge zeropage ok 154 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (2048 kB) ok 155 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (1048576 kB) ok 156 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with shared zeropage ok 157 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd ok 158 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with tmpfile ok 159 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with huge zeropage ok 160 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (2048 kB) ok 161 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (1048576 kB) ok 162 Longterm R/O pin is reliable Note 1: We don't care about short-term R/O-pinning, because they have snapshot semantics: they are not supposed to observe modifications that happen after pinning. As one example, assume we start direct I/O to read from a page and store page content into a file: modifications to page content after starting direct I/O are not guaranteed to end up in the file. So even if we'd pin the shared zeropage, the end result would be as expected -- getting zeroes stored to the file. Note 2: For shared mappings we'll now always fallback to the slow path to lookup the VMA when R/O long-term pining. While that's the necessary price we have to pay right now, it's actually not that bad in practice: most FOLL_LONGTERM users already specify FOLL_WRITE, for example, along with FOLL_FORCE because they tried dealing with COW mappings correctly ... Note 3: For users that use FOLL_LONGTERM right now without FOLL_WRITE, such as VFIO, we'd now no longer pin the shared zeropage. Instead, we'd populate exclusive anon pages that we can pin. There was a concern that this could affect the memlock limit of existing setups. For example, a VM running with VFIO could run into the memlock limit and fail to run. However, we essentially had the same behavior already in commit 17839856fd58 ("gup: document and work around "COW can break either way" issue") which got merged into some enterprise distros, and there were not any such complaints. So most probably, we're fine. Link: https://lkml.kernel.org/r/20221116102659.70287-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-16 18:26:48 +08:00
if (!pte_write(pte) && gup_must_unshare(NULL, flags, page)) {
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
gup_put_folio(folio, 1, flags);
goto pte_unmap;
}
mm/gup/writeback: add callbacks for inaccessible pages With the introduction of protected KVM guests on s390 there is now a concept of inaccessible pages. These pages need to be made accessible before the host can access them. While cpu accesses will trigger a fault that can be resolved, I/O accesses will just fail. We need to add a callback into architecture code for places that will do I/O, namely when writeback is started or when a page reference is taken. This is not only to enable paging, file backing etc, it is also necessary to protect the host against a malicious user space. For example a bad QEMU could simply start direct I/O on such protected memory. We do not want userspace to be able to trigger I/O errors and thus the logic is "whenever somebody accesses that page (gup) or does I/O, make sure that this page can be accessed". When the guest tries to access that page we will wait in the page fault handler for writeback to have finished and for the page_ref to be the expected value. On s390x the function is not supposed to fail, so it is ok to use a WARN_ON on failure. If we ever need some more finegrained handling we can tackle this when we know the details. Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Acked-by: Will Deacon <will@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Matthew Wilcox <willy@infradead.org> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200306132537.783769-3-imbrenda@linux.ibm.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:56 +08:00
/*
* We need to make the page accessible if and only if we are
* going to access its content (the FOLL_PIN case). Please
* see Documentation/core-api/pin_user_pages.rst for
* details.
*/
if (flags & FOLL_PIN) {
ret = arch_make_page_accessible(page);
if (ret) {
gup_put_folio(folio, 1, flags);
mm/gup/writeback: add callbacks for inaccessible pages With the introduction of protected KVM guests on s390 there is now a concept of inaccessible pages. These pages need to be made accessible before the host can access them. While cpu accesses will trigger a fault that can be resolved, I/O accesses will just fail. We need to add a callback into architecture code for places that will do I/O, namely when writeback is started or when a page reference is taken. This is not only to enable paging, file backing etc, it is also necessary to protect the host against a malicious user space. For example a bad QEMU could simply start direct I/O on such protected memory. We do not want userspace to be able to trigger I/O errors and thus the logic is "whenever somebody accesses that page (gup) or does I/O, make sure that this page can be accessed". When the guest tries to access that page we will wait in the page fault handler for writeback to have finished and for the page_ref to be the expected value. On s390x the function is not supposed to fail, so it is ok to use a WARN_ON on failure. If we ever need some more finegrained handling we can tackle this when we know the details. Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Acked-by: Will Deacon <will@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Matthew Wilcox <willy@infradead.org> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200306132537.783769-3-imbrenda@linux.ibm.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:56 +08:00
goto pte_unmap;
}
}
folio_set_referenced(folio);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
pages[*nr] = page;
(*nr)++;
} while (ptep++, addr += PAGE_SIZE, addr != end);
ret = 1;
pte_unmap:
if (pgmap)
put_dev_pagemap(pgmap);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
pte_unmap(ptem);
return ret;
}
#else
/*
* If we can't determine whether or not a pte is special, then fail immediately
* for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
* to be special.
*
* For a futex to be placed on a THP tail page, get_futex_key requires a
mm/gup.c: convert to use get_user_{page|pages}_fast_only() API __get_user_pages_fast() renamed to get_user_pages_fast_only() to align with pin_user_pages_fast_only(). As part of this we will get rid of write parameter. Instead caller will pass FOLL_WRITE to get_user_pages_fast_only(). This will not change any existing functionality of the API. All the callers are changed to pass FOLL_WRITE. Also introduce get_user_page_fast_only(), and use it in a few places that hard-code nr_pages to 1. Updated the documentation of the API. Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Paul Mackerras <paulus@ozlabs.org> [arch/powerpc/kvm] Cc: Matthew Wilcox <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Suchanek <msuchanek@suse.de> Link: http://lkml.kernel.org/r/1590396812-31277-1-git-send-email-jrdr.linux@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-08 12:40:55 +08:00
* get_user_pages_fast_only implementation that can pin pages. Thus it's still
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
* useful to have gup_huge_pmd even if we can't operate on ptes.
*/
mm: gup: fix the fast GUP race against THP collapse Since general RCU GUP fast was introduced in commit 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()"), a TLB flush is no longer sufficient to handle concurrent GUP-fast in all cases, it only handles traditional IPI-based GUP-fast correctly. On architectures that send an IPI broadcast on TLB flush, it works as expected. But on the architectures that do not use IPI to broadcast TLB flush, it may have the below race: CPU A CPU B THP collapse fast GUP gup_pmd_range() <-- see valid pmd gup_pte_range() <-- work on pte pmdp_collapse_flush() <-- clear pmd and flush __collapse_huge_page_isolate() check page pinned <-- before GUP bump refcount pin the page check PTE <-- no change __collapse_huge_page_copy() copy data to huge page ptep_clear() install huge pmd for the huge page return the stale page discard the stale page The race can be fixed by checking whether PMD is changed or not after taking the page pin in fast GUP, just like what it does for PTE. If the PMD is changed it means there may be parallel THP collapse, so GUP should back off. Also update the stale comment about serializing against fast GUP in khugepaged. Link: https://lkml.kernel.org/r/20220907180144.555485-1-shy828301@gmail.com Fixes: 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()") Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Peter Xu <peterx@redhat.com> Signed-off-by: Yang Shi <shy828301@gmail.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-09-08 02:01:43 +08:00
static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
{
return 0;
}
mm: introduce ARCH_HAS_PTE_SPECIAL Currently the PTE special supports is turned on in per architecture header files. Most of the time, it is defined in arch/*/include/asm/pgtable.h depending or not on some other per architecture static definition. This patch introduce a new configuration variable to manage this directly in the Kconfig files. It would later replace __HAVE_ARCH_PTE_SPECIAL. Here notes for some architecture where the definition of __HAVE_ARCH_PTE_SPECIAL is not obvious: arm __HAVE_ARCH_PTE_SPECIAL which is currently defined in arch/arm/include/asm/pgtable-3level.h which is included by arch/arm/include/asm/pgtable.h when CONFIG_ARM_LPAE is set. So select ARCH_HAS_PTE_SPECIAL if ARM_LPAE. powerpc __HAVE_ARCH_PTE_SPECIAL is defined in 2 files: - arch/powerpc/include/asm/book3s/64/pgtable.h - arch/powerpc/include/asm/pte-common.h The first one is included if (PPC_BOOK3S & PPC64) while the second is included in all the other cases. So select ARCH_HAS_PTE_SPECIAL all the time. sparc: __HAVE_ARCH_PTE_SPECIAL is defined if defined(__sparc__) && defined(__arch64__) which are defined through the compiler in sparc/Makefile if !SPARC32 which I assume to be if SPARC64. So select ARCH_HAS_PTE_SPECIAL if SPARC64 There is no functional change introduced by this patch. Link: http://lkml.kernel.org/r/1523433816-14460-2-git-send-email-ldufour@linux.vnet.ibm.com Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com> Suggested-by: Jerome Glisse <jglisse@redhat.com> Reviewed-by: Jerome Glisse <jglisse@redhat.com> Acked-by: David Rientjes <rientjes@google.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Rich Felker <dalias@libc.org> Cc: David S. Miller <davem@davemloft.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Vineet Gupta <vgupta@synopsys.com> Cc: Palmer Dabbelt <palmer@sifive.com> Cc: Albert Ou <albert@sifive.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: David Rientjes <rientjes@google.com> Cc: Robin Murphy <robin.murphy@arm.com> Cc: Christophe LEROY <christophe.leroy@c-s.fr> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-06-08 08:06:08 +08:00
#endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
#if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
static int __gup_device_huge(unsigned long pfn, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
int nr_start = *nr;
struct dev_pagemap *pgmap = NULL;
do {
struct page *page = pfn_to_page(pfn);
pgmap = get_dev_pagemap(pfn, pgmap);
if (unlikely(!pgmap)) {
undo_dev_pagemap(nr, nr_start, flags, pages);
break;
}
if (!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)) {
undo_dev_pagemap(nr, nr_start, flags, pages);
break;
}
SetPageReferenced(page);
pages[*nr] = page;
if (unlikely(try_grab_page(page, flags))) {
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
undo_dev_pagemap(nr, nr_start, flags, pages);
break;
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
}
(*nr)++;
pfn++;
} while (addr += PAGE_SIZE, addr != end);
put_dev_pagemap(pgmap);
return addr == end;
}
static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
unsigned long fault_pfn;
int nr_start = *nr;
fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
return 0;
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
undo_dev_pagemap(nr, nr_start, flags, pages);
return 0;
}
return 1;
}
static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
unsigned long fault_pfn;
int nr_start = *nr;
fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
return 0;
if (unlikely(pud_val(orig) != pud_val(*pudp))) {
undo_dev_pagemap(nr, nr_start, flags, pages);
return 0;
}
return 1;
}
#else
static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
BUILD_BUG();
return 0;
}
static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
BUILD_BUG();
return 0;
}
#endif
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
static int record_subpages(struct page *page, unsigned long addr,
unsigned long end, struct page **pages)
{
int nr;
for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
pages[nr] = nth_page(page, nr);
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
return nr;
}
#ifdef CONFIG_ARCH_HAS_HUGEPD
static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
unsigned long sz)
{
unsigned long __boundary = (addr + sz) & ~(sz-1);
return (__boundary - 1 < end - 1) ? __boundary : end;
}
static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
mm/gup: fix a misnamed "write" argument, and a related bug In several routines, the "flags" argument is incorrectly named "write". Change it to "flags". Also, in one place, the misnaming led to an actual bug: "flags & FOLL_WRITE" is required, rather than just "flags". (That problem was flagged by krobot, in v1 of this patch.) Also, change the flags argument from int, to unsigned int. You can see that this was a simple oversight, because the calling code passes "flags" to the fifth argument: gup_pgd_range(): ... if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, PGDIR_SHIFT, next, flags, pages, nr)) ...which, until this patch, the callees referred to as "write". Also, change two lines to avoid checkpatch line length complaints, and another line to fix another oversight that checkpatch called out: missing "int" on pdshift. Link: http://lkml.kernel.org/r/20191014184639.1512873-3-jhubbard@nvidia.com Fixes: b798bec4741b ("mm/gup: change write parameter to flags in fast walk") Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reported-by: kbuild test robot <lkp@intel.com> Suggested-by: Kirill A. Shutemov <kirill@shutemov.name> Suggested-by: Ira Weiny <ira.weiny@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Keith Busch <keith.busch@intel.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-10-19 11:19:53 +08:00
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
unsigned long pte_end;
struct page *page;
struct folio *folio;
pte_t pte;
int refs;
pte_end = (addr + sz) & ~(sz-1);
if (pte_end < end)
end = pte_end;
pte = huge_ptep_get(ptep);
mm/gup: fix a misnamed "write" argument, and a related bug In several routines, the "flags" argument is incorrectly named "write". Change it to "flags". Also, in one place, the misnaming led to an actual bug: "flags & FOLL_WRITE" is required, rather than just "flags". (That problem was flagged by krobot, in v1 of this patch.) Also, change the flags argument from int, to unsigned int. You can see that this was a simple oversight, because the calling code passes "flags" to the fifth argument: gup_pgd_range(): ... if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, PGDIR_SHIFT, next, flags, pages, nr)) ...which, until this patch, the callees referred to as "write". Also, change two lines to avoid checkpatch line length complaints, and another line to fix another oversight that checkpatch called out: missing "int" on pdshift. Link: http://lkml.kernel.org/r/20191014184639.1512873-3-jhubbard@nvidia.com Fixes: b798bec4741b ("mm/gup: change write parameter to flags in fast walk") Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reported-by: kbuild test robot <lkp@intel.com> Suggested-by: Kirill A. Shutemov <kirill@shutemov.name> Suggested-by: Ira Weiny <ira.weiny@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Keith Busch <keith.busch@intel.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-10-19 11:19:53 +08:00
if (!pte_access_permitted(pte, flags & FOLL_WRITE))
return 0;
/* hugepages are never "special" */
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = nth_page(pte_page(pte), (addr & (sz - 1)) >> PAGE_SHIFT);
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
refs = record_subpages(page, addr, end, pages + *nr);
folio = try_grab_folio(page, refs, flags);
if (!folio)
return 0;
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
gup_put_folio(folio, refs, flags);
return 0;
}
mm/gup: reliable R/O long-term pinning in COW mappings We already support reliable R/O pinning of anonymous memory. However, assume we end up pinning (R/O long-term) a pagecache page or the shared zeropage inside a writable private ("COW") mapping. The next write access will trigger a write-fault and replace the pinned page by an exclusive anonymous page in the process page tables to break COW: the pinned page no longer corresponds to the page mapped into the process' page table. Now that FAULT_FLAG_UNSHARE can break COW on anything mapped into a COW mapping, let's properly break COW first before R/O long-term pinning something that's not an exclusive anon page inside a COW mapping. FAULT_FLAG_UNSHARE will break COW and map an exclusive anon page instead that can get pinned safely. With this change, we can stop using FOLL_FORCE|FOLL_WRITE for reliable R/O long-term pinning in COW mappings. With this change, the new R/O long-term pinning tests for non-anonymous memory succeed: # [RUN] R/O longterm GUP pin ... with shared zeropage ok 151 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd ok 152 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with tmpfile ok 153 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with huge zeropage ok 154 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (2048 kB) ok 155 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (1048576 kB) ok 156 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with shared zeropage ok 157 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd ok 158 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with tmpfile ok 159 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with huge zeropage ok 160 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (2048 kB) ok 161 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (1048576 kB) ok 162 Longterm R/O pin is reliable Note 1: We don't care about short-term R/O-pinning, because they have snapshot semantics: they are not supposed to observe modifications that happen after pinning. As one example, assume we start direct I/O to read from a page and store page content into a file: modifications to page content after starting direct I/O are not guaranteed to end up in the file. So even if we'd pin the shared zeropage, the end result would be as expected -- getting zeroes stored to the file. Note 2: For shared mappings we'll now always fallback to the slow path to lookup the VMA when R/O long-term pining. While that's the necessary price we have to pay right now, it's actually not that bad in practice: most FOLL_LONGTERM users already specify FOLL_WRITE, for example, along with FOLL_FORCE because they tried dealing with COW mappings correctly ... Note 3: For users that use FOLL_LONGTERM right now without FOLL_WRITE, such as VFIO, we'd now no longer pin the shared zeropage. Instead, we'd populate exclusive anon pages that we can pin. There was a concern that this could affect the memlock limit of existing setups. For example, a VM running with VFIO could run into the memlock limit and fail to run. However, we essentially had the same behavior already in commit 17839856fd58 ("gup: document and work around "COW can break either way" issue") which got merged into some enterprise distros, and there were not any such complaints. So most probably, we're fine. Link: https://lkml.kernel.org/r/20221116102659.70287-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-16 18:26:48 +08:00
if (!pte_write(pte) && gup_must_unshare(NULL, flags, &folio->page)) {
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
gup_put_folio(folio, refs, flags);
return 0;
}
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
*nr += refs;
folio_set_referenced(folio);
return 1;
}
static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
mm/gup: fix a misnamed "write" argument, and a related bug In several routines, the "flags" argument is incorrectly named "write". Change it to "flags". Also, in one place, the misnaming led to an actual bug: "flags & FOLL_WRITE" is required, rather than just "flags". (That problem was flagged by krobot, in v1 of this patch.) Also, change the flags argument from int, to unsigned int. You can see that this was a simple oversight, because the calling code passes "flags" to the fifth argument: gup_pgd_range(): ... if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, PGDIR_SHIFT, next, flags, pages, nr)) ...which, until this patch, the callees referred to as "write". Also, change two lines to avoid checkpatch line length complaints, and another line to fix another oversight that checkpatch called out: missing "int" on pdshift. Link: http://lkml.kernel.org/r/20191014184639.1512873-3-jhubbard@nvidia.com Fixes: b798bec4741b ("mm/gup: change write parameter to flags in fast walk") Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reported-by: kbuild test robot <lkp@intel.com> Suggested-by: Kirill A. Shutemov <kirill@shutemov.name> Suggested-by: Ira Weiny <ira.weiny@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Keith Busch <keith.busch@intel.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-10-19 11:19:53 +08:00
unsigned int pdshift, unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
pte_t *ptep;
unsigned long sz = 1UL << hugepd_shift(hugepd);
unsigned long next;
ptep = hugepte_offset(hugepd, addr, pdshift);
do {
next = hugepte_addr_end(addr, end, sz);
mm/gup: fix a misnamed "write" argument, and a related bug In several routines, the "flags" argument is incorrectly named "write". Change it to "flags". Also, in one place, the misnaming led to an actual bug: "flags & FOLL_WRITE" is required, rather than just "flags". (That problem was flagged by krobot, in v1 of this patch.) Also, change the flags argument from int, to unsigned int. You can see that this was a simple oversight, because the calling code passes "flags" to the fifth argument: gup_pgd_range(): ... if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, PGDIR_SHIFT, next, flags, pages, nr)) ...which, until this patch, the callees referred to as "write". Also, change two lines to avoid checkpatch line length complaints, and another line to fix another oversight that checkpatch called out: missing "int" on pdshift. Link: http://lkml.kernel.org/r/20191014184639.1512873-3-jhubbard@nvidia.com Fixes: b798bec4741b ("mm/gup: change write parameter to flags in fast walk") Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reported-by: kbuild test robot <lkp@intel.com> Suggested-by: Kirill A. Shutemov <kirill@shutemov.name> Suggested-by: Ira Weiny <ira.weiny@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Keith Busch <keith.busch@intel.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-10-19 11:19:53 +08:00
if (!gup_hugepte(ptep, sz, addr, end, flags, pages, nr))
return 0;
} while (ptep++, addr = next, addr != end);
return 1;
}
#else
static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
mm/gup: fix a misnamed "write" argument, and a related bug In several routines, the "flags" argument is incorrectly named "write". Change it to "flags". Also, in one place, the misnaming led to an actual bug: "flags & FOLL_WRITE" is required, rather than just "flags". (That problem was flagged by krobot, in v1 of this patch.) Also, change the flags argument from int, to unsigned int. You can see that this was a simple oversight, because the calling code passes "flags" to the fifth argument: gup_pgd_range(): ... if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, PGDIR_SHIFT, next, flags, pages, nr)) ...which, until this patch, the callees referred to as "write". Also, change two lines to avoid checkpatch line length complaints, and another line to fix another oversight that checkpatch called out: missing "int" on pdshift. Link: http://lkml.kernel.org/r/20191014184639.1512873-3-jhubbard@nvidia.com Fixes: b798bec4741b ("mm/gup: change write parameter to flags in fast walk") Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reported-by: kbuild test robot <lkp@intel.com> Suggested-by: Kirill A. Shutemov <kirill@shutemov.name> Suggested-by: Ira Weiny <ira.weiny@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Keith Busch <keith.busch@intel.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-10-19 11:19:53 +08:00
unsigned int pdshift, unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
return 0;
}
#endif /* CONFIG_ARCH_HAS_HUGEPD */
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
mm/gup: fix a misnamed "write" argument, and a related bug In several routines, the "flags" argument is incorrectly named "write". Change it to "flags". Also, in one place, the misnaming led to an actual bug: "flags & FOLL_WRITE" is required, rather than just "flags". (That problem was flagged by krobot, in v1 of this patch.) Also, change the flags argument from int, to unsigned int. You can see that this was a simple oversight, because the calling code passes "flags" to the fifth argument: gup_pgd_range(): ... if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, PGDIR_SHIFT, next, flags, pages, nr)) ...which, until this patch, the callees referred to as "write". Also, change two lines to avoid checkpatch line length complaints, and another line to fix another oversight that checkpatch called out: missing "int" on pdshift. Link: http://lkml.kernel.org/r/20191014184639.1512873-3-jhubbard@nvidia.com Fixes: b798bec4741b ("mm/gup: change write parameter to flags in fast walk") Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reported-by: kbuild test robot <lkp@intel.com> Suggested-by: Kirill A. Shutemov <kirill@shutemov.name> Suggested-by: Ira Weiny <ira.weiny@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Keith Busch <keith.busch@intel.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-10-19 11:19:53 +08:00
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
{
struct page *page;
struct folio *folio;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
int refs;
if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
mm/gup: add FOLL_LONGTERM capability to GUP fast DAX pages were previously unprotected from longterm pins when users called get_user_pages_fast(). Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall back to regular GUP processing if a DEVMAP page is encountered. [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-5-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Hogan <jhogan@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Rich Felker <dalias@libc.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:14 +08:00
if (pmd_devmap(orig)) {
if (unlikely(flags & FOLL_LONGTERM))
return 0;
return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
pages, nr);
mm/gup: add FOLL_LONGTERM capability to GUP fast DAX pages were previously unprotected from longterm pins when users called get_user_pages_fast(). Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall back to regular GUP processing if a DEVMAP page is encountered. [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-5-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Hogan <jhogan@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Rich Felker <dalias@libc.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:14 +08:00
}
page = nth_page(pmd_page(orig), (addr & ~PMD_MASK) >> PAGE_SHIFT);
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
refs = record_subpages(page, addr, end, pages + *nr);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
folio = try_grab_folio(page, refs, flags);
if (!folio)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
gup_put_folio(folio, refs, flags);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
}
mm/gup: reliable R/O long-term pinning in COW mappings We already support reliable R/O pinning of anonymous memory. However, assume we end up pinning (R/O long-term) a pagecache page or the shared zeropage inside a writable private ("COW") mapping. The next write access will trigger a write-fault and replace the pinned page by an exclusive anonymous page in the process page tables to break COW: the pinned page no longer corresponds to the page mapped into the process' page table. Now that FAULT_FLAG_UNSHARE can break COW on anything mapped into a COW mapping, let's properly break COW first before R/O long-term pinning something that's not an exclusive anon page inside a COW mapping. FAULT_FLAG_UNSHARE will break COW and map an exclusive anon page instead that can get pinned safely. With this change, we can stop using FOLL_FORCE|FOLL_WRITE for reliable R/O long-term pinning in COW mappings. With this change, the new R/O long-term pinning tests for non-anonymous memory succeed: # [RUN] R/O longterm GUP pin ... with shared zeropage ok 151 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd ok 152 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with tmpfile ok 153 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with huge zeropage ok 154 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (2048 kB) ok 155 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (1048576 kB) ok 156 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with shared zeropage ok 157 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd ok 158 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with tmpfile ok 159 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with huge zeropage ok 160 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (2048 kB) ok 161 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (1048576 kB) ok 162 Longterm R/O pin is reliable Note 1: We don't care about short-term R/O-pinning, because they have snapshot semantics: they are not supposed to observe modifications that happen after pinning. As one example, assume we start direct I/O to read from a page and store page content into a file: modifications to page content after starting direct I/O are not guaranteed to end up in the file. So even if we'd pin the shared zeropage, the end result would be as expected -- getting zeroes stored to the file. Note 2: For shared mappings we'll now always fallback to the slow path to lookup the VMA when R/O long-term pining. While that's the necessary price we have to pay right now, it's actually not that bad in practice: most FOLL_LONGTERM users already specify FOLL_WRITE, for example, along with FOLL_FORCE because they tried dealing with COW mappings correctly ... Note 3: For users that use FOLL_LONGTERM right now without FOLL_WRITE, such as VFIO, we'd now no longer pin the shared zeropage. Instead, we'd populate exclusive anon pages that we can pin. There was a concern that this could affect the memlock limit of existing setups. For example, a VM running with VFIO could run into the memlock limit and fail to run. However, we essentially had the same behavior already in commit 17839856fd58 ("gup: document and work around "COW can break either way" issue") which got merged into some enterprise distros, and there were not any such complaints. So most probably, we're fine. Link: https://lkml.kernel.org/r/20221116102659.70287-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-16 18:26:48 +08:00
if (!pmd_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
gup_put_folio(folio, refs, flags);
return 0;
}
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
*nr += refs;
folio_set_referenced(folio);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 1;
}
static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
{
struct page *page;
struct folio *folio;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
int refs;
if (!pud_access_permitted(orig, flags & FOLL_WRITE))
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
mm/gup: add FOLL_LONGTERM capability to GUP fast DAX pages were previously unprotected from longterm pins when users called get_user_pages_fast(). Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall back to regular GUP processing if a DEVMAP page is encountered. [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-5-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Hogan <jhogan@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Rich Felker <dalias@libc.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:14 +08:00
if (pud_devmap(orig)) {
if (unlikely(flags & FOLL_LONGTERM))
return 0;
return __gup_device_huge_pud(orig, pudp, addr, end, flags,
pages, nr);
mm/gup: add FOLL_LONGTERM capability to GUP fast DAX pages were previously unprotected from longterm pins when users called get_user_pages_fast(). Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall back to regular GUP processing if a DEVMAP page is encountered. [ira.weiny@intel.com: v3] Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190328084422.29911-5-ira.weiny@intel.com Link: http://lkml.kernel.org/r/20190317183438.2057-5-ira.weiny@intel.com Signed-off-by: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Hogan <jhogan@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Rich Felker <dalias@libc.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: Mike Marshall <hubcap@omnibond.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 08:17:14 +08:00
}
page = nth_page(pud_page(orig), (addr & ~PUD_MASK) >> PAGE_SHIFT);
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
refs = record_subpages(page, addr, end, pages + *nr);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
folio = try_grab_folio(page, refs, flags);
if (!folio)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
if (unlikely(pud_val(orig) != pud_val(*pudp))) {
gup_put_folio(folio, refs, flags);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
}
mm/gup: reliable R/O long-term pinning in COW mappings We already support reliable R/O pinning of anonymous memory. However, assume we end up pinning (R/O long-term) a pagecache page or the shared zeropage inside a writable private ("COW") mapping. The next write access will trigger a write-fault and replace the pinned page by an exclusive anonymous page in the process page tables to break COW: the pinned page no longer corresponds to the page mapped into the process' page table. Now that FAULT_FLAG_UNSHARE can break COW on anything mapped into a COW mapping, let's properly break COW first before R/O long-term pinning something that's not an exclusive anon page inside a COW mapping. FAULT_FLAG_UNSHARE will break COW and map an exclusive anon page instead that can get pinned safely. With this change, we can stop using FOLL_FORCE|FOLL_WRITE for reliable R/O long-term pinning in COW mappings. With this change, the new R/O long-term pinning tests for non-anonymous memory succeed: # [RUN] R/O longterm GUP pin ... with shared zeropage ok 151 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd ok 152 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with tmpfile ok 153 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with huge zeropage ok 154 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (2048 kB) ok 155 Longterm R/O pin is reliable # [RUN] R/O longterm GUP pin ... with memfd hugetlb (1048576 kB) ok 156 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with shared zeropage ok 157 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd ok 158 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with tmpfile ok 159 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with huge zeropage ok 160 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (2048 kB) ok 161 Longterm R/O pin is reliable # [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (1048576 kB) ok 162 Longterm R/O pin is reliable Note 1: We don't care about short-term R/O-pinning, because they have snapshot semantics: they are not supposed to observe modifications that happen after pinning. As one example, assume we start direct I/O to read from a page and store page content into a file: modifications to page content after starting direct I/O are not guaranteed to end up in the file. So even if we'd pin the shared zeropage, the end result would be as expected -- getting zeroes stored to the file. Note 2: For shared mappings we'll now always fallback to the slow path to lookup the VMA when R/O long-term pining. While that's the necessary price we have to pay right now, it's actually not that bad in practice: most FOLL_LONGTERM users already specify FOLL_WRITE, for example, along with FOLL_FORCE because they tried dealing with COW mappings correctly ... Note 3: For users that use FOLL_LONGTERM right now without FOLL_WRITE, such as VFIO, we'd now no longer pin the shared zeropage. Instead, we'd populate exclusive anon pages that we can pin. There was a concern that this could affect the memlock limit of existing setups. For example, a VM running with VFIO could run into the memlock limit and fail to run. However, we essentially had the same behavior already in commit 17839856fd58 ("gup: document and work around "COW can break either way" issue") which got merged into some enterprise distros, and there were not any such complaints. So most probably, we're fine. Link: https://lkml.kernel.org/r/20221116102659.70287-10-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-11-16 18:26:48 +08:00
if (!pud_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
mm/gup: trigger FAULT_FLAG_UNSHARE when R/O-pinning a possibly shared anonymous page Whenever GUP currently ends up taking a R/O pin on an anonymous page that might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault on the page table entry will end up replacing the mapped anonymous page due to COW, resulting in the GUP pin no longer being consistent with the page actually mapped into the page table. The possible ways to deal with this situation are: (1) Ignore and pin -- what we do right now. (2) Fail to pin -- which would be rather surprising to callers and could break user space. (3) Trigger unsharing and pin the now exclusive page -- reliable R/O pins. Let's implement 3) because it provides the clearest semantics and allows for checking in unpin_user_pages() and friends for possible BUGs: when trying to unpin a page that's no longer exclusive, clearly something went very wrong and might result in memory corruptions that might be hard to debug. So we better have a nice way to spot such issues. This change implies that whenever user space *wrote* to a private mapping (IOW, we have an anonymous page mapped), that GUP pins will always remain consistent: reliable R/O GUP pins of anonymous pages. As a side note, this commit fixes the COW security issue for hugetlb with FOLL_PIN as documented in: https://lore.kernel.org/r/3ae33b08-d9ef-f846-56fb-645e3b9b4c66@redhat.com The vmsplice reproducer still applies, because vmsplice uses FOLL_GET instead of FOLL_PIN. Note that follow_huge_pmd() doesn't apply because we cannot end up in there with FOLL_PIN. This commit is heavily based on prototype patches by Andrea. Link: https://lkml.kernel.org/r/20220428083441.37290-17-david@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Co-developed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
gup_put_folio(folio, refs, flags);
return 0;
}
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
*nr += refs;
folio_set_referenced(folio);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 1;
}
static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
unsigned long end, unsigned int flags,
struct page **pages, int *nr)
{
int refs;
struct page *page;
struct folio *folio;
if (!pgd_access_permitted(orig, flags & FOLL_WRITE))
return 0;
BUILD_BUG_ON(pgd_devmap(orig));
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
page = nth_page(pgd_page(orig), (addr & ~PGDIR_MASK) >> PAGE_SHIFT);
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
refs = record_subpages(page, addr, end, pages + *nr);
folio = try_grab_folio(page, refs, flags);
if (!folio)
return 0;
if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
gup_put_folio(folio, refs, flags);
return 0;
}
mm/gup: factor out duplicate code from four routines Patch series "mm/gup: prereqs to track dma-pinned pages: FOLL_PIN", v12. Overview: This is a prerequisite to solving the problem of proper interactions between file-backed pages, and [R]DMA activities, as discussed in [1], [2], [3], and in a remarkable number of email threads since about 2017. :) A new internal gup flag, FOLL_PIN is introduced, and thoroughly documented in the last patch's Documentation/vm/pin_user_pages.rst. I believe that this will provide a good starting point for doing the layout lease work that Ira Weiny has been working on. That's because these new wrapper functions provide a clean, constrained, systematically named set of functionality that, again, is required in order to even know if a page is "dma-pinned". In contrast to earlier approaches, the page tracking can be incrementally applied to the kernel call sites that, until now, have been simply calling get_user_pages() ("gup"). In other words, opt-in by changing from this: get_user_pages() (sets FOLL_GET) put_page() to this: pin_user_pages() (sets FOLL_PIN) unpin_user_page() Testing: * I've done some overall kernel testing (LTP, and a few other goodies), and some directed testing to exercise some of the changes. And as you can see, gup_benchmark is enhanced to exercise this. Basically, I've been able to runtime test the core get_user_pages() and pin_user_pages() and related routines, but not so much on several of the call sites--but those are generally just a couple of lines changed, each. Not much of the kernel is actually using this, which on one hand reduces risk quite a lot. But on the other hand, testing coverage is low. So I'd love it if, in particular, the Infiniband and PowerPC folks could do a smoke test of this series for me. Runtime testing for the call sites so far is pretty light: * io_uring: Some directed tests from liburing exercise this, and they pass. * process_vm_access.c: A small directed test passes. * gup_benchmark: the enhanced version hits the new gup.c code, and passes. * infiniband: Ran rdma-core tests: rdma-core/build/bin/run_tests.py * VFIO: compiles (I'm vowing to set up a run time test soon, but it's not ready just yet) * powerpc: it compiles... * drm/via: compiles... * goldfish: compiles... * net/xdp: compiles... * media/v4l2: compiles... [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ This patch (of 22): There are four locations in gup.c that have a fair amount of code duplication. This means that changing one requires making the same changes in four places, not to mention reading the same code four times, and wondering if there are subtle differences. Factor out the common code into static functions, thus reducing the overall line count and the code's complexity. Also, take the opportunity to slightly improve the efficiency of the error cases, by doing a mass subtraction of the refcount, surrounded by get_page()/put_page(). Also, further simplify (slightly), by waiting until the the successful end of each routine, to increment *nr. Link: http://lkml.kernel.org/r/20200107224558.2362728-2-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:17 +08:00
*nr += refs;
folio_set_referenced(folio);
return 1;
}
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned long end,
unsigned int flags, struct page **pages, int *nr)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
{
unsigned long next;
pmd_t *pmdp;
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
pmdp = pmd_offset_lockless(pudp, pud, addr);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
do {
pmd_t pmd = pmdp_get_lockless(pmdp);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
next = pmd_addr_end(addr, end);
mm: thp: check pmd migration entry in common path When THP migration is being used, memory management code needs to handle pmd migration entries properly. This patch uses !pmd_present() or is_swap_pmd() (depending on whether pmd_none() needs separate code or not) to check pmd migration entries at the places where a pmd entry is present. Since pmd-related code uses split_huge_page(), split_huge_pmd(), pmd_trans_huge(), pmd_trans_unstable(), or pmd_none_or_trans_huge_or_clear_bad(), this patch: 1. adds pmd migration entry split code in split_huge_pmd(), 2. takes care of pmd migration entries whenever pmd_trans_huge() is present, 3. makes pmd_none_or_trans_huge_or_clear_bad() pmd migration entry aware. Since split_huge_page() uses split_huge_pmd() and pmd_trans_unstable() is equivalent to pmd_none_or_trans_huge_or_clear_bad(), we do not change them. Until this commit, a pmd entry should be: 1. pointing to a pte page, 2. is_swap_pmd(), 3. pmd_trans_huge(), 4. pmd_devmap(), or 5. pmd_none(). Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: David Nellans <dnellans@nvidia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Minchan Kim <minchan@kernel.org> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-09 07:11:01 +08:00
if (!pmd_present(pmd))
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) ||
pmd_devmap(pmd))) {
if (pmd_protnone(pmd) &&
!gup_can_follow_protnone(flags))
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
if (!gup_huge_pmd(pmd, pmdp, addr, next, flags,
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
pages, nr))
return 0;
} else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
/*
* architecture have different format for hugetlbfs
* pmd format and THP pmd format
*/
if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
PMD_SHIFT, next, flags, pages, nr))
return 0;
mm: gup: fix the fast GUP race against THP collapse Since general RCU GUP fast was introduced in commit 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()"), a TLB flush is no longer sufficient to handle concurrent GUP-fast in all cases, it only handles traditional IPI-based GUP-fast correctly. On architectures that send an IPI broadcast on TLB flush, it works as expected. But on the architectures that do not use IPI to broadcast TLB flush, it may have the below race: CPU A CPU B THP collapse fast GUP gup_pmd_range() <-- see valid pmd gup_pte_range() <-- work on pte pmdp_collapse_flush() <-- clear pmd and flush __collapse_huge_page_isolate() check page pinned <-- before GUP bump refcount pin the page check PTE <-- no change __collapse_huge_page_copy() copy data to huge page ptep_clear() install huge pmd for the huge page return the stale page discard the stale page The race can be fixed by checking whether PMD is changed or not after taking the page pin in fast GUP, just like what it does for PTE. If the PMD is changed it means there may be parallel THP collapse, so GUP should back off. Also update the stale comment about serializing against fast GUP in khugepaged. Link: https://lkml.kernel.org/r/20220907180144.555485-1-shy828301@gmail.com Fixes: 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()") Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Peter Xu <peterx@redhat.com> Signed-off-by: Yang Shi <shy828301@gmail.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-09-08 02:01:43 +08:00
} else if (!gup_pte_range(pmd, pmdp, addr, next, flags, pages, nr))
return 0;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
} while (pmdp++, addr = next, addr != end);
return 1;
}
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned long end,
unsigned int flags, struct page **pages, int *nr)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
{
unsigned long next;
pud_t *pudp;
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
pudp = pud_offset_lockless(p4dp, p4d, addr);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
do {
pud_t pud = READ_ONCE(*pudp);
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
next = pud_addr_end(addr, end);
if (unlikely(!pud_present(pud)))
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
mm/gup: fix gup_pud_range() for dax For dax pud, pud_huge() returns true on x86. So the function works as long as hugetlb is configured. However, dax doesn't depend on hugetlb. Commit 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax") fixed devmap-backed huge PMDs, but missed devmap-backed huge PUDs. Fix this as well. This fixes the below kernel panic: general protection fault, probably for non-canonical address 0x69e7c000cc478: 0000 [#1] SMP < snip > Call Trace: <TASK> get_user_pages_fast+0x1f/0x40 iov_iter_get_pages+0xc6/0x3b0 ? mempool_alloc+0x5d/0x170 bio_iov_iter_get_pages+0x82/0x4e0 ? bvec_alloc+0x91/0xc0 ? bio_alloc_bioset+0x19a/0x2a0 blkdev_direct_IO+0x282/0x480 ? __io_complete_rw_common+0xc0/0xc0 ? filemap_range_has_page+0x82/0xc0 generic_file_direct_write+0x9d/0x1a0 ? inode_update_time+0x24/0x30 __generic_file_write_iter+0xbd/0x1e0 blkdev_write_iter+0xb4/0x150 ? io_import_iovec+0x8d/0x340 io_write+0xf9/0x300 io_issue_sqe+0x3c3/0x1d30 ? sysvec_reschedule_ipi+0x6c/0x80 __io_queue_sqe+0x33/0x240 ? fget+0x76/0xa0 io_submit_sqes+0xe6a/0x18d0 ? __fget_light+0xd1/0x100 __x64_sys_io_uring_enter+0x199/0x880 ? __context_tracking_enter+0x1f/0x70 ? irqentry_exit_to_user_mode+0x24/0x30 ? irqentry_exit+0x1d/0x30 ? __context_tracking_exit+0xe/0x70 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7fc97c11a7be < snip > </TASK> ---[ end trace 48b2e0e67debcaeb ]--- RIP: 0010:internal_get_user_pages_fast+0x340/0x990 < snip > Kernel panic - not syncing: Fatal exception Kernel Offset: disabled Link: https://lkml.kernel.org/r/1670392853-28252-1-git-send-email-ssengar@linux.microsoft.com Fixes: 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax") Signed-off-by: John Starks <jostarks@microsoft.com> Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com> Cc: Jan Kara <jack@suse.cz> Cc: Yu Zhao <yuzhao@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: David Hildenbrand <david@redhat.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-12-07 14:00:53 +08:00
if (unlikely(pud_huge(pud) || pud_devmap(pud))) {
if (!gup_huge_pud(pud, pudp, addr, next, flags,
pages, nr))
return 0;
} else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
PUD_SHIFT, next, flags, pages, nr))
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
} else if (!gup_pmd_range(pudp, pud, addr, next, flags, pages, nr))
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
return 0;
} while (pudp++, addr = next, addr != end);
return 1;
}
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
static int gup_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, unsigned long end,
unsigned int flags, struct page **pages, int *nr)
{
unsigned long next;
p4d_t *p4dp;
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
p4dp = p4d_offset_lockless(pgdp, pgd, addr);
do {
p4d_t p4d = READ_ONCE(*p4dp);
next = p4d_addr_end(addr, end);
if (p4d_none(p4d))
return 0;
BUILD_BUG_ON(p4d_huge(p4d));
if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) {
if (!gup_huge_pd(__hugepd(p4d_val(p4d)), addr,
P4D_SHIFT, next, flags, pages, nr))
return 0;
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
} else if (!gup_pud_range(p4dp, p4d, addr, next, flags, pages, nr))
return 0;
} while (p4dp++, addr = next, addr != end);
return 1;
}
static void gup_pgd_range(unsigned long addr, unsigned long end,
unsigned int flags, struct page **pages, int *nr)
{
unsigned long next;
pgd_t *pgdp;
pgdp = pgd_offset(current->mm, addr);
do {
pgd_t pgd = READ_ONCE(*pgdp);
next = pgd_addr_end(addr, end);
if (pgd_none(pgd))
return;
if (unlikely(pgd_huge(pgd))) {
if (!gup_huge_pgd(pgd, pgdp, addr, next, flags,
pages, nr))
return;
} else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
PGDIR_SHIFT, next, flags, pages, nr))
return;
mm/gup: fix gup_fast with dynamic page table folding Currently to make sure that every page table entry is read just once gup_fast walks perform READ_ONCE and pass pXd value down to the next gup_pXd_range function by value e.g.: static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) ... pudp = pud_offset(&p4d, addr); This function passes a reference on that local value copy to pXd_offset, and might get the very same pointer in return. This happens when the level is folded (on most arches), and that pointer should not be iterated. On s390 due to the fact that each task might have different 5,4 or 3-level address translation and hence different levels folded the logic is more complex and non-iteratable pointer to a local copy leads to severe problems. Here is an example of what happens with gup_fast on s390, for a task with 3-level paging, crossing a 2 GB pud boundary: // addr = 0x1007ffff000, end = 0x10080001000 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end, unsigned int flags, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; // pud_offset returns &p4d itself (a pointer to a value on stack) pudp = pud_offset(&p4d, addr); do { // on second iteratation reading "random" stack value pud_t pud = READ_ONCE(*pudp); // next = 0x10080000000, due to PUD_SIZE/MASK != PGDIR_SIZE/MASK on s390 next = pud_addr_end(addr, end); ... } while (pudp++, addr = next, addr != end); // pudp++ iterating over stack return 1; } This happens since s390 moved to common gup code with commit d1874a0c2805 ("s390/mm: make the pxd_offset functions more robust") and commit 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code"). s390 tried to mimic static level folding by changing pXd_offset primitives to always calculate top level page table offset in pgd_offset and just return the value passed when pXd_offset has to act as folded. What is crucial for gup_fast and what has been overlooked is that PxD_SIZE/MASK and thus pXd_addr_end should also change correspondingly. And the latter is not possible with dynamic folding. To fix the issue in addition to pXd values pass original pXdp pointers down to gup_pXd_range functions. And introduce pXd_offset_lockless helpers, which take an additional pXd entry value parameter. This has already been discussed in https://lkml.kernel.org/r/20190418100218.0a4afd51@mschwideX1 Fixes: 1a42010cdc26 ("s390/mm: convert to the generic get_user_pages_fast code") Signed-off-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: <stable@vger.kernel.org> [5.2+] Link: https://lkml.kernel.org/r/patch.git-943f1e5dcff2.your-ad-here.call-01599856292-ext-8676@work.hours Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-26 12:19:10 +08:00
} else if (!gup_p4d_range(pgdp, pgd, addr, next, flags, pages, nr))
return;
} while (pgdp++, addr = next, addr != end);
}
#else
static inline void gup_pgd_range(unsigned long addr, unsigned long end,
unsigned int flags, struct page **pages, int *nr)
{
}
#endif /* CONFIG_HAVE_FAST_GUP */
#ifndef gup_fast_permitted
/*
mm/gup.c: convert to use get_user_{page|pages}_fast_only() API __get_user_pages_fast() renamed to get_user_pages_fast_only() to align with pin_user_pages_fast_only(). As part of this we will get rid of write parameter. Instead caller will pass FOLL_WRITE to get_user_pages_fast_only(). This will not change any existing functionality of the API. All the callers are changed to pass FOLL_WRITE. Also introduce get_user_page_fast_only(), and use it in a few places that hard-code nr_pages to 1. Updated the documentation of the API. Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Paul Mackerras <paulus@ozlabs.org> [arch/powerpc/kvm] Cc: Matthew Wilcox <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Suchanek <msuchanek@suse.de> Link: http://lkml.kernel.org/r/1590396812-31277-1-git-send-email-jrdr.linux@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-08 12:40:55 +08:00
* Check if it's allowed to use get_user_pages_fast_only() for the range, or
* we need to fall back to the slow version:
*/
static bool gup_fast_permitted(unsigned long start, unsigned long end)
{
return true;
}
#endif
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
static unsigned long lockless_pages_from_mm(unsigned long start,
unsigned long end,
unsigned int gup_flags,
struct page **pages)
{
unsigned long flags;
int nr_pinned = 0;
mm/gup: prevent gup_fast from racing with COW during fork Since commit 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes") pages under a FOLL_PIN will not be write protected during COW for fork. This means that pages returned from pin_user_pages(FOLL_WRITE) should not become write protected while the pin is active. However, there is a small race where get_user_pages_fast(FOLL_PIN) can establish a FOLL_PIN at the same time copy_present_page() is write protecting it: CPU 0 CPU 1 get_user_pages_fast() internal_get_user_pages_fast() copy_page_range() pte_alloc_map_lock() copy_present_page() atomic_read(has_pinned) == 0 page_maybe_dma_pinned() == false atomic_set(has_pinned, 1); gup_pgd_range() gup_pte_range() pte_t pte = gup_get_pte(ptep) pte_access_permitted(pte) try_grab_compound_head() pte = pte_wrprotect(pte) set_pte_at(); pte_unmap_unlock() // GUP now returns with a write protected page The first attempt to resolve this by using the write protect caused problems (and was missing a barrrier), see commit f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Instead wrap copy_p4d_range() with the write side of a seqcount and check the read side around gup_pgd_range(). If there is a collision then get_user_pages_fast() fails and falls back to slow GUP. Slow GUP is safe against this race because copy_page_range() is only called while holding the exclusive side of the mmap_lock on the src mm_struct. [akpm@linux-foundation.org: coding style fixes] Link: https://lore.kernel.org/r/CAHk-=wi=iCnYCARbPGjkVJu9eyYeZ13N64tZYLdOB8CP5Q_PLw@mail.gmail.com Link: https://lkml.kernel.org/r/2-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Fixes: f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Peter Xu <peterx@redhat.com> Acked-by: "Ahmed S. Darwish" <a.darwish@linutronix.de> [seqcount_t parts] Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kirill Shutemov <kirill@shutemov.name> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Leon Romanovsky <leonro@nvidia.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:44 +08:00
unsigned seq;
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) ||
!gup_fast_permitted(start, end))
return 0;
mm/gup: prevent gup_fast from racing with COW during fork Since commit 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes") pages under a FOLL_PIN will not be write protected during COW for fork. This means that pages returned from pin_user_pages(FOLL_WRITE) should not become write protected while the pin is active. However, there is a small race where get_user_pages_fast(FOLL_PIN) can establish a FOLL_PIN at the same time copy_present_page() is write protecting it: CPU 0 CPU 1 get_user_pages_fast() internal_get_user_pages_fast() copy_page_range() pte_alloc_map_lock() copy_present_page() atomic_read(has_pinned) == 0 page_maybe_dma_pinned() == false atomic_set(has_pinned, 1); gup_pgd_range() gup_pte_range() pte_t pte = gup_get_pte(ptep) pte_access_permitted(pte) try_grab_compound_head() pte = pte_wrprotect(pte) set_pte_at(); pte_unmap_unlock() // GUP now returns with a write protected page The first attempt to resolve this by using the write protect caused problems (and was missing a barrrier), see commit f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Instead wrap copy_p4d_range() with the write side of a seqcount and check the read side around gup_pgd_range(). If there is a collision then get_user_pages_fast() fails and falls back to slow GUP. Slow GUP is safe against this race because copy_page_range() is only called while holding the exclusive side of the mmap_lock on the src mm_struct. [akpm@linux-foundation.org: coding style fixes] Link: https://lore.kernel.org/r/CAHk-=wi=iCnYCARbPGjkVJu9eyYeZ13N64tZYLdOB8CP5Q_PLw@mail.gmail.com Link: https://lkml.kernel.org/r/2-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Fixes: f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Peter Xu <peterx@redhat.com> Acked-by: "Ahmed S. Darwish" <a.darwish@linutronix.de> [seqcount_t parts] Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kirill Shutemov <kirill@shutemov.name> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Leon Romanovsky <leonro@nvidia.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:44 +08:00
if (gup_flags & FOLL_PIN) {
seq = raw_read_seqcount(&current->mm->write_protect_seq);
if (seq & 1)
return 0;
}
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
/*
* Disable interrupts. The nested form is used, in order to allow full,
* general purpose use of this routine.
*
* With interrupts disabled, we block page table pages from being freed
* from under us. See struct mmu_table_batch comments in
* include/asm-generic/tlb.h for more details.
*
* We do not adopt an rcu_read_lock() here as we also want to block IPIs
* that come from THPs splitting.
*/
local_irq_save(flags);
gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
local_irq_restore(flags);
mm/gup: prevent gup_fast from racing with COW during fork Since commit 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes") pages under a FOLL_PIN will not be write protected during COW for fork. This means that pages returned from pin_user_pages(FOLL_WRITE) should not become write protected while the pin is active. However, there is a small race where get_user_pages_fast(FOLL_PIN) can establish a FOLL_PIN at the same time copy_present_page() is write protecting it: CPU 0 CPU 1 get_user_pages_fast() internal_get_user_pages_fast() copy_page_range() pte_alloc_map_lock() copy_present_page() atomic_read(has_pinned) == 0 page_maybe_dma_pinned() == false atomic_set(has_pinned, 1); gup_pgd_range() gup_pte_range() pte_t pte = gup_get_pte(ptep) pte_access_permitted(pte) try_grab_compound_head() pte = pte_wrprotect(pte) set_pte_at(); pte_unmap_unlock() // GUP now returns with a write protected page The first attempt to resolve this by using the write protect caused problems (and was missing a barrrier), see commit f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Instead wrap copy_p4d_range() with the write side of a seqcount and check the read side around gup_pgd_range(). If there is a collision then get_user_pages_fast() fails and falls back to slow GUP. Slow GUP is safe against this race because copy_page_range() is only called while holding the exclusive side of the mmap_lock on the src mm_struct. [akpm@linux-foundation.org: coding style fixes] Link: https://lore.kernel.org/r/CAHk-=wi=iCnYCARbPGjkVJu9eyYeZ13N64tZYLdOB8CP5Q_PLw@mail.gmail.com Link: https://lkml.kernel.org/r/2-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Fixes: f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Peter Xu <peterx@redhat.com> Acked-by: "Ahmed S. Darwish" <a.darwish@linutronix.de> [seqcount_t parts] Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kirill Shutemov <kirill@shutemov.name> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Leon Romanovsky <leonro@nvidia.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:44 +08:00
/*
* When pinning pages for DMA there could be a concurrent write protect
* from fork() via copy_page_range(), in this case always fail fast GUP.
*/
if (gup_flags & FOLL_PIN) {
if (read_seqcount_retry(&current->mm->write_protect_seq, seq)) {
mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Let's verify when (un)pinning anonymous pages that we always deal with exclusive anonymous pages, which guarantees that we'll have a reliable PIN, meaning that we cannot end up with the GUP pin being inconsistent with he pages mapped into the page tables due to a COW triggered by a write fault. When pinning pages, after conditionally triggering GUP unsharing of possibly shared anonymous pages, we should always only see exclusive anonymous pages. Note that anonymous pages that are mapped writable must be marked exclusive, otherwise we'd have a BUG. When pinning during ordinary GUP, simply add a check after our conditional GUP-triggered unsharing checks. As we know exactly how the page is mapped, we know exactly in which page we have to check for PageAnonExclusive(). When pinning via GUP-fast we have to be careful, because we can race with fork(): verify only after we made sure via the seqcount that we didn't race with concurrent fork() that we didn't end up pinning a possibly shared anonymous page. Similarly, when unpinning, verify that the pages are still marked as exclusive: otherwise something turned the pages possibly shared, which can result in random memory corruptions, which we really want to catch. With only the pinned pages at hand and not the actual page table entries we have to be a bit careful: hugetlb pages are always mapped via a single logical page table entry referencing the head page and PG_anon_exclusive of the head page applies. Anon THP are a bit more complicated, because we might have obtained the page reference either via a PMD or a PTE -- depending on the mapping type we either have to check PageAnonExclusive of the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies: as we don't know and to make our life easier, check that either is set. Take care to not verify in case we're unpinning during GUP-fast because we detected concurrent fork(): we might stumble over an anonymous page that is now shared. Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
unpin_user_pages_lockless(pages, nr_pinned);
mm/gup: prevent gup_fast from racing with COW during fork Since commit 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes") pages under a FOLL_PIN will not be write protected during COW for fork. This means that pages returned from pin_user_pages(FOLL_WRITE) should not become write protected while the pin is active. However, there is a small race where get_user_pages_fast(FOLL_PIN) can establish a FOLL_PIN at the same time copy_present_page() is write protecting it: CPU 0 CPU 1 get_user_pages_fast() internal_get_user_pages_fast() copy_page_range() pte_alloc_map_lock() copy_present_page() atomic_read(has_pinned) == 0 page_maybe_dma_pinned() == false atomic_set(has_pinned, 1); gup_pgd_range() gup_pte_range() pte_t pte = gup_get_pte(ptep) pte_access_permitted(pte) try_grab_compound_head() pte = pte_wrprotect(pte) set_pte_at(); pte_unmap_unlock() // GUP now returns with a write protected page The first attempt to resolve this by using the write protect caused problems (and was missing a barrrier), see commit f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Instead wrap copy_p4d_range() with the write side of a seqcount and check the read side around gup_pgd_range(). If there is a collision then get_user_pages_fast() fails and falls back to slow GUP. Slow GUP is safe against this race because copy_page_range() is only called while holding the exclusive side of the mmap_lock on the src mm_struct. [akpm@linux-foundation.org: coding style fixes] Link: https://lore.kernel.org/r/CAHk-=wi=iCnYCARbPGjkVJu9eyYeZ13N64tZYLdOB8CP5Q_PLw@mail.gmail.com Link: https://lkml.kernel.org/r/2-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Fixes: f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Peter Xu <peterx@redhat.com> Acked-by: "Ahmed S. Darwish" <a.darwish@linutronix.de> [seqcount_t parts] Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kirill Shutemov <kirill@shutemov.name> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Leon Romanovsky <leonro@nvidia.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:44 +08:00
return 0;
mm/gup: sanity-check with CONFIG_DEBUG_VM that anonymous pages are exclusive when (un)pinning Let's verify when (un)pinning anonymous pages that we always deal with exclusive anonymous pages, which guarantees that we'll have a reliable PIN, meaning that we cannot end up with the GUP pin being inconsistent with he pages mapped into the page tables due to a COW triggered by a write fault. When pinning pages, after conditionally triggering GUP unsharing of possibly shared anonymous pages, we should always only see exclusive anonymous pages. Note that anonymous pages that are mapped writable must be marked exclusive, otherwise we'd have a BUG. When pinning during ordinary GUP, simply add a check after our conditional GUP-triggered unsharing checks. As we know exactly how the page is mapped, we know exactly in which page we have to check for PageAnonExclusive(). When pinning via GUP-fast we have to be careful, because we can race with fork(): verify only after we made sure via the seqcount that we didn't race with concurrent fork() that we didn't end up pinning a possibly shared anonymous page. Similarly, when unpinning, verify that the pages are still marked as exclusive: otherwise something turned the pages possibly shared, which can result in random memory corruptions, which we really want to catch. With only the pinned pages at hand and not the actual page table entries we have to be a bit careful: hugetlb pages are always mapped via a single logical page table entry referencing the head page and PG_anon_exclusive of the head page applies. Anon THP are a bit more complicated, because we might have obtained the page reference either via a PMD or a PTE -- depending on the mapping type we either have to check PageAnonExclusive of the head page (PMD-mapped THP) or the tail page (PTE-mapped THP) applies: as we don't know and to make our life easier, check that either is set. Take care to not verify in case we're unpinning during GUP-fast because we detected concurrent fork(): we might stumble over an anonymous page that is now shared. Link: https://lkml.kernel.org/r/20220428083441.37290-18-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Khalid Aziz <khalid.aziz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <namit@vmware.com> Cc: Oded Gabbay <oded.gabbay@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <guro@fb.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-10 09:20:45 +08:00
} else {
sanity_check_pinned_pages(pages, nr_pinned);
mm/gup: prevent gup_fast from racing with COW during fork Since commit 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes") pages under a FOLL_PIN will not be write protected during COW for fork. This means that pages returned from pin_user_pages(FOLL_WRITE) should not become write protected while the pin is active. However, there is a small race where get_user_pages_fast(FOLL_PIN) can establish a FOLL_PIN at the same time copy_present_page() is write protecting it: CPU 0 CPU 1 get_user_pages_fast() internal_get_user_pages_fast() copy_page_range() pte_alloc_map_lock() copy_present_page() atomic_read(has_pinned) == 0 page_maybe_dma_pinned() == false atomic_set(has_pinned, 1); gup_pgd_range() gup_pte_range() pte_t pte = gup_get_pte(ptep) pte_access_permitted(pte) try_grab_compound_head() pte = pte_wrprotect(pte) set_pte_at(); pte_unmap_unlock() // GUP now returns with a write protected page The first attempt to resolve this by using the write protect caused problems (and was missing a barrrier), see commit f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Instead wrap copy_p4d_range() with the write side of a seqcount and check the read side around gup_pgd_range(). If there is a collision then get_user_pages_fast() fails and falls back to slow GUP. Slow GUP is safe against this race because copy_page_range() is only called while holding the exclusive side of the mmap_lock on the src mm_struct. [akpm@linux-foundation.org: coding style fixes] Link: https://lore.kernel.org/r/CAHk-=wi=iCnYCARbPGjkVJu9eyYeZ13N64tZYLdOB8CP5Q_PLw@mail.gmail.com Link: https://lkml.kernel.org/r/2-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Fixes: f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Peter Xu <peterx@redhat.com> Acked-by: "Ahmed S. Darwish" <a.darwish@linutronix.de> [seqcount_t parts] Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kirill Shutemov <kirill@shutemov.name> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Leon Romanovsky <leonro@nvidia.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:44 +08:00
}
}
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
return nr_pinned;
}
static int internal_get_user_pages_fast(unsigned long start,
unsigned long nr_pages,
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
unsigned int gup_flags,
struct page **pages)
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
{
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
unsigned long len, end;
unsigned long nr_pinned;
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
int locked = 0;
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
int ret;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
mm/gup: allow FOLL_FORCE for get_user_pages_fast() Commit 817be129e6f2 ("mm: validate get_user_pages_fast flags") allowed only FOLL_WRITE and FOLL_LONGTERM to be passed to get_user_pages_fast(). This, combined with the fact that get_user_pages_fast() falls back to "slow gup", which *does* accept FOLL_FORCE, leads to an odd situation: if you need FOLL_FORCE, you cannot call get_user_pages_fast(). There does not appear to be any reason for filtering out FOLL_FORCE. There is nothing in the _fast() implementation that requires that we avoid writing to the pages. So it appears to have been an oversight. Fix by allowing FOLL_FORCE to be set for get_user_pages_fast(). Link: http://lkml.kernel.org/r/20200107224558.2362728-9-jhubbard@nvidia.com Fixes: 817be129e6f2 ("mm: validate get_user_pages_fast flags") Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Leon Romanovsky <leonro@mellanox.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Christoph Hellwig <hch@lst.de> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:43 +08:00
if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
mm/gup: refactor and de-duplicate gup_fast() code There were two nearly identical sets of code for gup_fast() style of walking the page tables with interrupts disabled. This has lead to the usual maintenance problems that arise from having duplicated code. There is already a core internal routine in gup.c for gup_fast(), so just enhance it very slightly: allow skipping the fall-back to "slow" (regular) get_user_pages(), via the new FOLL_FAST_ONLY flag. Then, just call internal_get_user_pages_fast() from __get_user_pages_fast(), and adjust the API to match pre-existing API behavior. There is a change in behavior from this refactoring: the nested form of interrupt disabling is used in all gup_fast() variants now. That's because there is only one place that interrupt disabling for page walking is done, and so the safer form is required. This should, if anything, eliminate possible (rare) bugs, because the non-nested form of enabling interrupts was fragile at best. [jhubbard@nvidia.com: fixup] Link: http://lkml.kernel.org/r/20200521233841.1279742-1-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Souptick Joarder <jrdr.linux@gmail.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://lkml.kernel.org/r/20200519002124.2025955-3-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-04 06:56:30 +08:00
FOLL_FORCE | FOLL_PIN | FOLL_GET |
FOLL_FAST_ONLY | FOLL_NOFAULT |
FOLL_PCI_P2PDMA)))
return -EINVAL;
mm: gup: pack has_pinned in MMF_HAS_PINNED has_pinned 32bit can be packed in the MMF_HAS_PINNED bit as a noop cleanup. Any atomic_inc/dec to the mm cacheline shared by all threads in pin-fast would reintroduce a loss of SMP scalability to pin-fast, so there's no future potential usefulness to keep an atomic in the mm for this. set_bit(MMF_HAS_PINNED) will be theoretically a bit slower than WRITE_ONCE (atomic_set is equivalent to WRITE_ONCE), but the set_bit (just like atomic_set after this commit) has to be still issued only once per "mm", so the difference between the two will be lost in the noise. will-it-scale "mmap2" shows no change in performance with enterprise config as expected. will-it-scale "pin_fast" retains the > 4000% SMP scalability performance improvement against upstream as expected. This is a noop as far as overall performance and SMP scalability are concerned. [peterx@redhat.com: pack has_pinned in MMF_HAS_PINNED] Link: https://lkml.kernel.org/r/YJqWESqyxa8OZA+2@t490s [akpm@linux-foundation.org: coding style fixes] [peterx@redhat.com: fix build for task_mmu.c, introduce mm_set_has_pinned_flag, fix comments] Link: https://lkml.kernel.org/r/20210507150553.208763-4-peterx@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Kirill Shutemov <kirill@shutemov.name> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:36:40 +08:00
if (gup_flags & FOLL_PIN)
mm_set_has_pinned_flag(&current->mm->flags);
if (!(gup_flags & FOLL_FAST_ONLY))
might_lock_read(&current->mm->mmap_lock);
start = untagged_addr(start) & PAGE_MASK;
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
len = nr_pages << PAGE_SHIFT;
if (check_add_overflow(start, len, &end))
get_user_pages_fast(): return -EFAULT on access_ok failure get_user_pages_fast is supposed to be a faster drop-in equivalent of get_user_pages. As such, callers expect it to return a negative return code when passed an invalid address, and never expect it to return 0 when passed a positive number of pages, since its documentation says: * Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages * were pinned, returns -errno. When get_user_pages_fast fall back on get_user_pages this is exactly what happens. Unfortunately the implementation is inconsistent: it returns 0 if passed a kernel address, confusing callers: for example, the following is pretty common but does not appear to do the right thing with a kernel address: ret = get_user_pages_fast(addr, 1, writeable, &page); if (ret < 0) return ret; Change get_user_pages_fast to return -EFAULT when supplied a kernel address to make it match expectations. All callers have been audited for consistency with the documented semantics. Link: http://lkml.kernel.org/r/1522962072-182137-4-git-send-email-mst@redhat.com Fixes: 5b65c4677a57 ("mm, x86/mm: Fix performance regression in get_user_pages_fast()") Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Reported-by: syzbot+6304bf97ef436580fede@syzkaller.appspotmail.com Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Thorsten Leemhuis <regressions@leemhuis.info> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-04-14 06:35:20 +08:00
return 0;
x86-64: make access_ok() independent of LAM The linear address masking (LAM) code made access_ok() more complicated, in that it now needs to untag the address in order to verify the access range. See commit 74c228d20a51 ("x86/uaccess: Provide untagged_addr() and remove tags before address check"). We were able to avoid that overhead in the get_user/put_user code paths by simply using the sign bit for the address check, and depending on the GP fault if the address was non-canonical, which made it all independent of LAM. And we can do the same thing for access_ok(): simply check that the user pointer range has the high bit clear. No need to bother with any address bit masking. In fact, we can go a bit further, and just check the starting address for known small accesses ranges: any accesses that overflow will still be in the non-canonical area and will still GP fault. To still make syzkaller catch any potentially unchecked user addresses, we'll continue to warn about GP faults that are caused by accesses in the non-canonical range. But we'll limit that to purely "high bit set and past the one-page 'slop' area". We could probably just do that "check only starting address" for any arbitrary range size: realistically all kernel accesses to user space will be done starting at the low address. But let's leave that kind of optimization for later. As it is, this already allows us to generate simpler code and not worry about any tag bits in the address. The one thing to look out for is the GUP address check: instead of actually copying data in the virtual address range (and thus bad addresses being caught by the GP fault), GUP will look up the page tables manually. As a result, the page table limits need to be checked, and that was previously implicitly done by the access_ok(). With the relaxed access_ok() check, we need to just do an explicit check for TASK_SIZE_MAX in the GUP code instead. The GUP code already needs to do the tag bit unmasking anyway, so there this is all very straightforward, and there are no LAM issues. Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2023-04-29 03:55:10 +08:00
if (end > TASK_SIZE_MAX)
return -EFAULT;
Remove 'type' argument from access_ok() function Nobody has actually used the type (VERIFY_READ vs VERIFY_WRITE) argument of the user address range verification function since we got rid of the old racy i386-only code to walk page tables by hand. It existed because the original 80386 would not honor the write protect bit when in kernel mode, so you had to do COW by hand before doing any user access. But we haven't supported that in a long time, and these days the 'type' argument is a purely historical artifact. A discussion about extending 'user_access_begin()' to do the range checking resulted this patch, because there is no way we're going to move the old VERIFY_xyz interface to that model. And it's best done at the end of the merge window when I've done most of my merges, so let's just get this done once and for all. This patch was mostly done with a sed-script, with manual fix-ups for the cases that weren't of the trivial 'access_ok(VERIFY_xyz' form. There were a couple of notable cases: - csky still had the old "verify_area()" name as an alias. - the iter_iov code had magical hardcoded knowledge of the actual values of VERIFY_{READ,WRITE} (not that they mattered, since nothing really used it) - microblaze used the type argument for a debug printout but other than those oddities this should be a total no-op patch. I tried to fix up all architectures, did fairly extensive grepping for access_ok() uses, and the changes are trivial, but I may have missed something. Any missed conversion should be trivially fixable, though. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-01-04 10:57:57 +08:00
if (unlikely(!access_ok((void __user *)start, len)))
get_user_pages_fast(): return -EFAULT on access_ok failure get_user_pages_fast is supposed to be a faster drop-in equivalent of get_user_pages. As such, callers expect it to return a negative return code when passed an invalid address, and never expect it to return 0 when passed a positive number of pages, since its documentation says: * Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages * were pinned, returns -errno. When get_user_pages_fast fall back on get_user_pages this is exactly what happens. Unfortunately the implementation is inconsistent: it returns 0 if passed a kernel address, confusing callers: for example, the following is pretty common but does not appear to do the right thing with a kernel address: ret = get_user_pages_fast(addr, 1, writeable, &page); if (ret < 0) return ret; Change get_user_pages_fast to return -EFAULT when supplied a kernel address to make it match expectations. All callers have been audited for consistency with the documented semantics. Link: http://lkml.kernel.org/r/1522962072-182137-4-git-send-email-mst@redhat.com Fixes: 5b65c4677a57 ("mm, x86/mm: Fix performance regression in get_user_pages_fast()") Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Reported-by: syzbot+6304bf97ef436580fede@syzkaller.appspotmail.com Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Thorsten Leemhuis <regressions@leemhuis.info> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-04-14 06:35:20 +08:00
return -EFAULT;
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages);
if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY)
return nr_pinned;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
/* Slow path: try to get the remaining pages with get_user_pages */
start += nr_pinned << PAGE_SHIFT;
pages += nr_pinned;
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
ret = __gup_longterm_locked(current->mm, start, nr_pages - nr_pinned,
pages, NULL, &locked,
gup_flags | FOLL_TOUCH | FOLL_UNLOCKABLE);
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
if (ret < 0) {
/*
* The caller has to unpin the pages we already pinned so
* returning -errno is not an option
*/
if (nr_pinned)
return nr_pinned;
return ret;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
}
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
return ret + nr_pinned;
mm: introduce a general RCU get_user_pages_fast() This series implements general forms of get_user_pages_fast and __get_user_pages_fast in core code and activates them for arm and arm64. These are required for Transparent HugePages to function correctly, as a futex on a THP tail will otherwise result in an infinite loop (due to the core implementation of __get_user_pages_fast always returning 0). Unfortunately, a futex on THP tail can be quite common for certain workloads; thus THP is unreliable without a __get_user_pages_fast implementation. This series may also be beneficial for direct-IO heavy workloads and certain KVM workloads. This patch (of 6): get_user_pages_fast() attempts to pin user pages by walking the page tables directly and avoids taking locks. Thus the walker needs to be protected from page table pages being freed from under it, and needs to block any THP splits. One way to achieve this is to have the walker disable interrupts, and rely on IPIs from the TLB flushing code blocking before the page table pages are freed. On some platforms we have hardware broadcast of TLB invalidations, thus the TLB flushing code doesn't necessarily need to broadcast IPIs; and spuriously broadcasting IPIs can hurt system performance if done too often. This problem has been solved on PowerPC and Sparc by batching up page table pages belonging to more than one mm_user, then scheduling an rcu_sched callback to free the pages. This RCU page table free logic has been promoted to core code and is activated when one enables HAVE_RCU_TABLE_FREE. Unfortunately, these architectures implement their own get_user_pages_fast routines. The RCU page table free logic coupled with an IPI broadcast on THP split (which is a rare event), allows one to protect a page table walker by merely disabling the interrupts during the walk. This patch provides a general RCU implementation of get_user_pages_fast that can be used by architectures that perform hardware broadcast of TLB invalidations. It is based heavily on the PowerPC implementation by Nick Piggin. [akpm@linux-foundation.org: various comment fixes] Signed-off-by: Steve Capper <steve.capper@linaro.org> Tested-by: Dann Frazier <dann.frazier@canonical.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Will Deacon <will.deacon@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-10 06:29:14 +08:00
}
mm/gup: reorganize internal_get_user_pages_fast() Patch series "Add a seqcount between gup_fast and copy_page_range()", v4. As discussed and suggested by Linus use a seqcount to close the small race between gup_fast and copy_page_range(). Ahmed confirms that raw_write_seqcount_begin() is the correct API to use in this case and it doesn't trigger any lockdeps. I was able to test it using two threads, one forking and the other using ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep made the window large enough to reliably hit to test the logic. This patch (of 2): The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Link: https://lkml.kernel.org/r/0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-12-15 11:05:41 +08:00
mm/gup.c: convert to use get_user_{page|pages}_fast_only() API __get_user_pages_fast() renamed to get_user_pages_fast_only() to align with pin_user_pages_fast_only(). As part of this we will get rid of write parameter. Instead caller will pass FOLL_WRITE to get_user_pages_fast_only(). This will not change any existing functionality of the API. All the callers are changed to pass FOLL_WRITE. Also introduce get_user_page_fast_only(), and use it in a few places that hard-code nr_pages to 1. Updated the documentation of the API. Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Paul Mackerras <paulus@ozlabs.org> [arch/powerpc/kvm] Cc: Matthew Wilcox <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Suchanek <msuchanek@suse.de> Link: http://lkml.kernel.org/r/1590396812-31277-1-git-send-email-jrdr.linux@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-08 12:40:55 +08:00
/**
* get_user_pages_fast_only() - pin user pages in memory
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying pin behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long.
*
mm/gup: move __get_user_pages_fast() down a few lines in gup.c Patch series "mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()", v2. In order to convert the drm/i915 driver from get_user_pages() to pin_user_pages(), a FOLL_PIN equivalent of __get_user_pages_fast() was required. That led to refactoring __get_user_pages_fast(), with the following goals: 1) As above: provide a pin_user_pages*() routine for drm/i915 to call, in place of __get_user_pages_fast(), 2) Get rid of the gup.c duplicate code for walking page tables with interrupts disabled. This duplicate code is a minor maintenance problem anyway. 3) Make it easy for an upcoming patch from Souptick, which aims to convert __get_user_pages_fast() to use a gup_flags argument, instead of a bool writeable arg. Also, if this series looks good, we can ask Souptick to change the name as well, to whatever the consensus is. My initial recommendation is: get_user_pages_fast_only(), to match the new pin_user_pages_only(). This patch (of 4): This is in order to avoid a forward declaration of internal_get_user_pages_fast(), in the next patch. This is code movement only--all generated code should be identical. Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Souptick Joarder <jrdr.linux@gmail.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://lkml.kernel.org/r/20200522051931.54191-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-2-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-04 06:56:27 +08:00
* Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
* the regular GUP.
*
* If the architecture does not support this function, simply return with no
* pages pinned.
*
* Careful, careful! COW breaking can go either way, so a non-write
* access can get ambiguous page results. If you call this function without
* 'write' set, you'd better be sure that you're ok with that ambiguity.
*/
mm/gup.c: convert to use get_user_{page|pages}_fast_only() API __get_user_pages_fast() renamed to get_user_pages_fast_only() to align with pin_user_pages_fast_only(). As part of this we will get rid of write parameter. Instead caller will pass FOLL_WRITE to get_user_pages_fast_only(). This will not change any existing functionality of the API. All the callers are changed to pass FOLL_WRITE. Also introduce get_user_page_fast_only(), and use it in a few places that hard-code nr_pages to 1. Updated the documentation of the API. Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Paul Mackerras <paulus@ozlabs.org> [arch/powerpc/kvm] Cc: Matthew Wilcox <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Suchanek <msuchanek@suse.de> Link: http://lkml.kernel.org/r/1590396812-31277-1-git-send-email-jrdr.linux@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-08 12:40:55 +08:00
int get_user_pages_fast_only(unsigned long start, int nr_pages,
unsigned int gup_flags, struct page **pages)
mm/gup: move __get_user_pages_fast() down a few lines in gup.c Patch series "mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()", v2. In order to convert the drm/i915 driver from get_user_pages() to pin_user_pages(), a FOLL_PIN equivalent of __get_user_pages_fast() was required. That led to refactoring __get_user_pages_fast(), with the following goals: 1) As above: provide a pin_user_pages*() routine for drm/i915 to call, in place of __get_user_pages_fast(), 2) Get rid of the gup.c duplicate code for walking page tables with interrupts disabled. This duplicate code is a minor maintenance problem anyway. 3) Make it easy for an upcoming patch from Souptick, which aims to convert __get_user_pages_fast() to use a gup_flags argument, instead of a bool writeable arg. Also, if this series looks good, we can ask Souptick to change the name as well, to whatever the consensus is. My initial recommendation is: get_user_pages_fast_only(), to match the new pin_user_pages_only(). This patch (of 4): This is in order to avoid a forward declaration of internal_get_user_pages_fast(), in the next patch. This is code movement only--all generated code should be identical. Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Souptick Joarder <jrdr.linux@gmail.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://lkml.kernel.org/r/20200522051931.54191-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-2-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-04 06:56:27 +08:00
{
/*
* Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
* because gup fast is always a "pin with a +1 page refcount" request.
mm/gup: refactor and de-duplicate gup_fast() code There were two nearly identical sets of code for gup_fast() style of walking the page tables with interrupts disabled. This has lead to the usual maintenance problems that arise from having duplicated code. There is already a core internal routine in gup.c for gup_fast(), so just enhance it very slightly: allow skipping the fall-back to "slow" (regular) get_user_pages(), via the new FOLL_FAST_ONLY flag. Then, just call internal_get_user_pages_fast() from __get_user_pages_fast(), and adjust the API to match pre-existing API behavior. There is a change in behavior from this refactoring: the nested form of interrupt disabling is used in all gup_fast() variants now. That's because there is only one place that interrupt disabling for page walking is done, and so the safer form is required. This should, if anything, eliminate possible (rare) bugs, because the non-nested form of enabling interrupts was fragile at best. [jhubbard@nvidia.com: fixup] Link: http://lkml.kernel.org/r/20200521233841.1279742-1-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Souptick Joarder <jrdr.linux@gmail.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://lkml.kernel.org/r/20200519002124.2025955-3-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-04 06:56:30 +08:00
*
* FOLL_FAST_ONLY is required in order to match the API description of
* this routine: no fall back to regular ("slow") GUP.
mm/gup: move __get_user_pages_fast() down a few lines in gup.c Patch series "mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()", v2. In order to convert the drm/i915 driver from get_user_pages() to pin_user_pages(), a FOLL_PIN equivalent of __get_user_pages_fast() was required. That led to refactoring __get_user_pages_fast(), with the following goals: 1) As above: provide a pin_user_pages*() routine for drm/i915 to call, in place of __get_user_pages_fast(), 2) Get rid of the gup.c duplicate code for walking page tables with interrupts disabled. This duplicate code is a minor maintenance problem anyway. 3) Make it easy for an upcoming patch from Souptick, which aims to convert __get_user_pages_fast() to use a gup_flags argument, instead of a bool writeable arg. Also, if this series looks good, we can ask Souptick to change the name as well, to whatever the consensus is. My initial recommendation is: get_user_pages_fast_only(), to match the new pin_user_pages_only(). This patch (of 4): This is in order to avoid a forward declaration of internal_get_user_pages_fast(), in the next patch. This is code movement only--all generated code should be identical. Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Souptick Joarder <jrdr.linux@gmail.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://lkml.kernel.org/r/20200522051931.54191-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-2-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-04 06:56:27 +08:00
*/
if (!is_valid_gup_args(pages, NULL, NULL, &gup_flags,
FOLL_GET | FOLL_FAST_ONLY))
return -EINVAL;
mm/gup: move __get_user_pages_fast() down a few lines in gup.c Patch series "mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()", v2. In order to convert the drm/i915 driver from get_user_pages() to pin_user_pages(), a FOLL_PIN equivalent of __get_user_pages_fast() was required. That led to refactoring __get_user_pages_fast(), with the following goals: 1) As above: provide a pin_user_pages*() routine for drm/i915 to call, in place of __get_user_pages_fast(), 2) Get rid of the gup.c duplicate code for walking page tables with interrupts disabled. This duplicate code is a minor maintenance problem anyway. 3) Make it easy for an upcoming patch from Souptick, which aims to convert __get_user_pages_fast() to use a gup_flags argument, instead of a bool writeable arg. Also, if this series looks good, we can ask Souptick to change the name as well, to whatever the consensus is. My initial recommendation is: get_user_pages_fast_only(), to match the new pin_user_pages_only(). This patch (of 4): This is in order to avoid a forward declaration of internal_get_user_pages_fast(), in the next patch. This is code movement only--all generated code should be identical. Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Souptick Joarder <jrdr.linux@gmail.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://lkml.kernel.org/r/20200522051931.54191-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-2-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-04 06:56:27 +08:00
return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
mm/gup: move __get_user_pages_fast() down a few lines in gup.c Patch series "mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()", v2. In order to convert the drm/i915 driver from get_user_pages() to pin_user_pages(), a FOLL_PIN equivalent of __get_user_pages_fast() was required. That led to refactoring __get_user_pages_fast(), with the following goals: 1) As above: provide a pin_user_pages*() routine for drm/i915 to call, in place of __get_user_pages_fast(), 2) Get rid of the gup.c duplicate code for walking page tables with interrupts disabled. This duplicate code is a minor maintenance problem anyway. 3) Make it easy for an upcoming patch from Souptick, which aims to convert __get_user_pages_fast() to use a gup_flags argument, instead of a bool writeable arg. Also, if this series looks good, we can ask Souptick to change the name as well, to whatever the consensus is. My initial recommendation is: get_user_pages_fast_only(), to match the new pin_user_pages_only(). This patch (of 4): This is in order to avoid a forward declaration of internal_get_user_pages_fast(), in the next patch. This is code movement only--all generated code should be identical. Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Souptick Joarder <jrdr.linux@gmail.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://lkml.kernel.org/r/20200522051931.54191-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-2-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-04 06:56:27 +08:00
}
mm/gup.c: convert to use get_user_{page|pages}_fast_only() API __get_user_pages_fast() renamed to get_user_pages_fast_only() to align with pin_user_pages_fast_only(). As part of this we will get rid of write parameter. Instead caller will pass FOLL_WRITE to get_user_pages_fast_only(). This will not change any existing functionality of the API. All the callers are changed to pass FOLL_WRITE. Also introduce get_user_page_fast_only(), and use it in a few places that hard-code nr_pages to 1. Updated the documentation of the API. Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Paul Mackerras <paulus@ozlabs.org> [arch/powerpc/kvm] Cc: Matthew Wilcox <willy@infradead.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Michal Suchanek <msuchanek@suse.de> Link: http://lkml.kernel.org/r/1590396812-31277-1-git-send-email-jrdr.linux@gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-08 12:40:55 +08:00
EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
mm/gup: move __get_user_pages_fast() down a few lines in gup.c Patch series "mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()", v2. In order to convert the drm/i915 driver from get_user_pages() to pin_user_pages(), a FOLL_PIN equivalent of __get_user_pages_fast() was required. That led to refactoring __get_user_pages_fast(), with the following goals: 1) As above: provide a pin_user_pages*() routine for drm/i915 to call, in place of __get_user_pages_fast(), 2) Get rid of the gup.c duplicate code for walking page tables with interrupts disabled. This duplicate code is a minor maintenance problem anyway. 3) Make it easy for an upcoming patch from Souptick, which aims to convert __get_user_pages_fast() to use a gup_flags argument, instead of a bool writeable arg. Also, if this series looks good, we can ask Souptick to change the name as well, to whatever the consensus is. My initial recommendation is: get_user_pages_fast_only(), to match the new pin_user_pages_only(). This patch (of 4): This is in order to avoid a forward declaration of internal_get_user_pages_fast(), in the next patch. This is code movement only--all generated code should be identical. Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: David Airlie <airlied@linux.ie> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com> Cc: Matthew Auld <matthew.auld@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Souptick Joarder <jrdr.linux@gmail.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: http://lkml.kernel.org/r/20200522051931.54191-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-1-jhubbard@nvidia.com Link: http://lkml.kernel.org/r/20200519002124.2025955-2-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-04 06:56:27 +08:00
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
/**
* get_user_pages_fast() - pin user pages in memory
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying pin behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long.
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
*
* Attempt to pin user pages in memory without taking mm->mmap_lock.
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
* If not successful, it will fall back to taking the lock and
* calling get_user_pages().
*
* Returns number of pages pinned. This may be fewer than the number requested.
* If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns
* -errno.
*/
int get_user_pages_fast(unsigned long start, int nr_pages,
unsigned int gup_flags, struct page **pages)
{
/*
* The caller may or may not have explicitly set FOLL_GET; either way is
* OK. However, internally (within mm/gup.c), gup fast variants must set
* FOLL_GET, because gup fast is always a "pin with a +1 page refcount"
* request.
*/
if (!is_valid_gup_args(pages, NULL, NULL, &gup_flags, FOLL_GET))
return -EINVAL;
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
}
EXPORT_SYMBOL_GPL(get_user_pages_fast);
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
/**
* pin_user_pages_fast() - pin user pages in memory without taking locks
*
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying pin behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long.
*
* Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
* get_user_pages_fast() for documentation on the function arguments, because
* the arguments here are identical.
*
* FOLL_PIN means that the pages must be released via unpin_user_page(). Please
* see Documentation/core-api/pin_user_pages.rst for further details.
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
*/
int pin_user_pages_fast(unsigned long start, int nr_pages,
unsigned int gup_flags, struct page **pages)
{
if (!is_valid_gup_args(pages, NULL, NULL, &gup_flags, FOLL_PIN))
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
return -EINVAL;
return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
}
EXPORT_SYMBOL_GPL(pin_user_pages_fast);
/**
* pin_user_pages_remote() - pin pages of a remote process
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
*
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
* @mm: mm_struct of target mm
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying lookup behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long.
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
* @vmas: array of pointers to vmas corresponding to each page.
* Or NULL if the caller does not require them.
* @locked: pointer to lock flag indicating whether lock is held and
* subsequently whether VM_FAULT_RETRY functionality can be
* utilised. Lock must initially be held.
*
* Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See
* get_user_pages_remote() for documentation on the function arguments, because
* the arguments here are identical.
*
* FOLL_PIN means that the pages must be released via unpin_user_page(). Please
* see Documentation/core-api/pin_user_pages.rst for details.
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
*/
long pin_user_pages_remote(struct mm_struct *mm,
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas, int *locked)
{
int local_locked = 1;
if (!is_valid_gup_args(pages, vmas, locked, &gup_flags,
FOLL_PIN | FOLL_TOUCH | FOLL_REMOTE))
return 0;
return __gup_longterm_locked(mm, start, nr_pages, pages, vmas,
locked ? locked : &local_locked,
gup_flags);
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
}
EXPORT_SYMBOL(pin_user_pages_remote);
/**
* pin_user_pages() - pin user pages in memory for use by other devices
*
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying lookup behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long.
mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK). Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Suggested-by: Jan Kara <jack@suse.cz> Suggested-by: Jérôme Glisse <jglisse@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Jan Kara <jack@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 12:05:29 +08:00
* @vmas: array of pointers to vmas corresponding to each page.
* Or NULL if the caller does not require them.
*
* Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and
* FOLL_PIN is set.
*
* FOLL_PIN means that the pages must be released via unpin_user_page(). Please
* see Documentation/core-api/pin_user_pages.rst for details.
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
*/
long pin_user_pages(unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas)
{
int locked = 1;
if (!is_valid_gup_args(pages, vmas, NULL, &gup_flags, FOLL_PIN))
return 0;
return __gup_longterm_locked(current->mm, start, nr_pages,
pages, vmas, &locked, gup_flags);
mm/gup: introduce pin_user_pages*() and FOLL_PIN Introduce pin_user_pages*() variations of get_user_pages*() calls, and also pin_longterm_pages*() variations. For now, these are placeholder calls, until the various call sites are converted to use the correct get_user_pages*() or pin_user_pages*() API. These variants will eventually all set FOLL_PIN, which is also introduced, and thoroughly documented. pin_user_pages() pin_user_pages_remote() pin_user_pages_fast() All pages that are pinned via the above calls, must be unpinned via put_user_page(). The underlying rules are: * FOLL_PIN is a gup-internal flag, so the call sites should not directly set it. That behavior is enforced with assertions. * Call sites that want to indicate that they are going to do DirectIO ("DIO") or something with similar characteristics, should call a get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers will: * Start with "pin_user_pages" instead of "get_user_pages". That makes it easy to find and audit the call sites. * Set FOLL_PIN * For pages that are received via FOLL_PIN, those pages must be returned via put_user_page(). Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded upon it.) Link: http://lkml.kernel.org/r/20200107224558.2362728-12-jhubbard@nvidia.com Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> [Documentation] Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Björn Töpel <bjorn.topel@intel.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jens Axboe <axboe@kernel.dk> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Leon Romanovsky <leonro@mellanox.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-01-31 14:12:54 +08:00
}
EXPORT_SYMBOL(pin_user_pages);
/*
* pin_user_pages_unlocked() is the FOLL_PIN variant of
* get_user_pages_unlocked(). Behavior is the same, except that this one sets
* FOLL_PIN and rejects FOLL_GET.
*/
long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
struct page **pages, unsigned int gup_flags)
{
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
int locked = 0;
if (!is_valid_gup_args(pages, NULL, NULL, &gup_flags,
FOLL_PIN | FOLL_TOUCH | FOLL_UNLOCKABLE))
return 0;
mm/gup: have internal functions get the mmap_read_lock() Patch series "Simplify the external interface for GUP", v2. It is quite a maze of EXPORTED symbols leading up to the three actual worker functions of GUP. Simplify this by reorganizing some of the code so the EXPORTED symbols directly call the correct internal function with validated and consistent arguments. Consolidate all the assertions into one place at the top of the call chains. Remove some dead code. Move more things into the mm/internal.h header This patch (of 13): __get_user_pages_locked() and __gup_longterm_locked() both require the mmap lock to be held. They have a slightly unusual locked parameter that is used to allow these functions to unlock and relock the mmap lock and convey that fact to the caller. Several places wrap these functions with a simple mmap_read_lock() just so they can follow the optimized locked protocol. Consolidate this internally to the functions. Allow internal callers to set locked = 0 to cause the functions to acquire and release the lock on their own. Reorganize __gup_longterm_locked() to use the autolocking in __get_user_pages_locked(). Replace all the places obtaining the mmap_read_lock() just to call __get_user_pages_locked() with the new mechanism. Replace all the internal callers of get_user_pages_unlocked() with direct calls to __gup_longterm_locked() using the new mechanism. A following patch will add assertions ensuring the external interface continues to always pass in locked = 1. Link: https://lkml.kernel.org/r/0-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Link: https://lkml.kernel.org/r/1-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-25 04:34:22 +08:00
return __gup_longterm_locked(current->mm, start, nr_pages, pages, NULL,
&locked, gup_flags);
}
EXPORT_SYMBOL(pin_user_pages_unlocked);