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mm: move the migrate_vma_* device migration code into its own file 

Split the code used to migrate to and from ZONE_DEVICE memory from
migrate.c into a new file.

Link: https://lkml.kernel.org/r/20220210072828.2930359-14-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: "Sierra Guiza, Alejandro (Alex)" <alex.sierra@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Cc: Christian Knig <christian.koenig@amd.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
This commit is contained in:
Christoph Hellwig 2022-02-16 15:31:38 +11:00 committed by Matthew Wilcox (Oracle)
parent aaf7d70cc5
commit 76cbbead25
4 changed files with 770 additions and 753 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
mm/Kconfig
View File

@ -249,6 +249,9 @@ config MIGRATION
pages as migration can relocate pages to satisfy a huge page
allocation instead of reclaiming.
config DEVICE_MIGRATION
def_bool MIGRATION && DEVICE_PRIVATE
config ARCH_ENABLE_HUGEPAGE_MIGRATION
bool

1
mm/Makefile
View File

@ -92,6 +92,7 @@ obj-$(CONFIG_KFENCE) += kfence/
obj-$(CONFIG_FAILSLAB) += failslab.o
obj-$(CONFIG_MEMTEST) += memtest.o
obj-$(CONFIG_MIGRATION) += migrate.o
obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o
obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o
obj-$(CONFIG_PAGE_COUNTER) += page_counter.o
obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o

753
mm/migrate.c
View File

@ -38,12 +38,10 @@
#include <linux/hugetlb.h>
#include <linux/hugetlb_cgroup.h>
#include <linux/gfp.h>
#include <linux/pagewalk.h>
#include <linux/pfn_t.h>
#include <linux/memremap.h>
#include <linux/userfaultfd_k.h>
#include <linux/balloon_compaction.h>
#include <linux/mmu_notifier.h>
#include <linux/page_idle.h>
#include <linux/page_owner.h>
#include <linux/sched/mm.h>
@ -2129,757 +2127,6 @@ out:
#endif /* CONFIG_NUMA_BALANCING */
#endif /* CONFIG_NUMA */
#ifdef CONFIG_DEVICE_PRIVATE
static int migrate_vma_collect_skip(unsigned long start,
unsigned long end,
struct mm_walk *walk)
{
struct migrate_vma *migrate = walk->private;
unsigned long addr;
for (addr = start; addr < end; addr += PAGE_SIZE) {
migrate->dst[migrate->npages] = 0;
migrate->src[migrate->npages++] = 0;
}
return 0;
}
static int migrate_vma_collect_hole(unsigned long start,
unsigned long end,
__always_unused int depth,
struct mm_walk *walk)
{
struct migrate_vma *migrate = walk->private;
unsigned long addr;
/* Only allow populating anonymous memory. */
if (!vma_is_anonymous(walk->vma))
return migrate_vma_collect_skip(start, end, walk);
for (addr = start; addr < end; addr += PAGE_SIZE) {
migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
migrate->dst[migrate->npages] = 0;
migrate->npages++;
migrate->cpages++;
}
return 0;
}
static int migrate_vma_collect_pmd(pmd_t *pmdp,
unsigned long start,
unsigned long end,
struct mm_walk *walk)
{
struct migrate_vma *migrate = walk->private;
struct vm_area_struct *vma = walk->vma;
struct mm_struct *mm = vma->vm_mm;
unsigned long addr = start, unmapped = 0;
spinlock_t *ptl;
pte_t *ptep;
again:
if (pmd_none(*pmdp))
return migrate_vma_collect_hole(start, end, -1, walk);
if (pmd_trans_huge(*pmdp)) {
struct page *page;
ptl = pmd_lock(mm, pmdp);
if (unlikely(!pmd_trans_huge(*pmdp))) {
spin_unlock(ptl);
goto again;
}
page = pmd_page(*pmdp);
if (is_huge_zero_page(page)) {
spin_unlock(ptl);
split_huge_pmd(vma, pmdp, addr);
if (pmd_trans_unstable(pmdp))
return migrate_vma_collect_skip(start, end,
walk);
} else {
int ret;
get_page(page);
spin_unlock(ptl);
if (unlikely(!trylock_page(page)))
return migrate_vma_collect_skip(start, end,
walk);
ret = split_huge_page(page);
unlock_page(page);
put_page(page);
if (ret)
return migrate_vma_collect_skip(start, end,
walk);
if (pmd_none(*pmdp))
return migrate_vma_collect_hole(start, end, -1,
walk);
}
}
if (unlikely(pmd_bad(*pmdp)))
return migrate_vma_collect_skip(start, end, walk);
ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
arch_enter_lazy_mmu_mode();
for (; addr < end; addr += PAGE_SIZE, ptep++) {
unsigned long mpfn = 0, pfn;
struct page *page;
swp_entry_t entry;
pte_t pte;
pte = *ptep;
if (pte_none(pte)) {
if (vma_is_anonymous(vma)) {
mpfn = MIGRATE_PFN_MIGRATE;
migrate->cpages++;
}
goto next;
}
if (!pte_present(pte)) {
/*
* Only care about unaddressable device page special
* page table entry. Other special swap entries are not
* migratable, and we ignore regular swapped page.
*/
entry = pte_to_swp_entry(pte);
if (!is_device_private_entry(entry))
goto next;
page = pfn_swap_entry_to_page(entry);
if (!(migrate->flags &
MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
page->pgmap->owner != migrate->pgmap_owner)
goto next;
mpfn = migrate_pfn(page_to_pfn(page)) |
MIGRATE_PFN_MIGRATE;
if (is_writable_device_private_entry(entry))
mpfn |= MIGRATE_PFN_WRITE;
} else {
if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
goto next;
pfn = pte_pfn(pte);
if (is_zero_pfn(pfn)) {
mpfn = MIGRATE_PFN_MIGRATE;
migrate->cpages++;
goto next;
}
page = vm_normal_page(migrate->vma, addr, pte);
mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
}
/* FIXME support THP */
if (!page || !page->mapping || PageTransCompound(page)) {
mpfn = 0;
goto next;
}
/*
* By getting a reference on the page we pin it and that blocks
* any kind of migration. Side effect is that it "freezes" the
* pte.
*
* We drop this reference after isolating the page from the lru
* for non device page (device page are not on the lru and thus
* can't be dropped from it).
*/
get_page(page);
/*
* Optimize for the common case where page is only mapped once
* in one process. If we can lock the page, then we can safely
* set up a special migration page table entry now.
*/
if (trylock_page(page)) {
pte_t swp_pte;
migrate->cpages++;
ptep_get_and_clear(mm, addr, ptep);
/* Setup special migration page table entry */
if (mpfn & MIGRATE_PFN_WRITE)
entry = make_writable_migration_entry(
page_to_pfn(page));
else
entry = make_readable_migration_entry(
page_to_pfn(page));
swp_pte = swp_entry_to_pte(entry);
if (pte_present(pte)) {
if (pte_soft_dirty(pte))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_uffd_wp(pte))
swp_pte = pte_swp_mkuffd_wp(swp_pte);
} else {
if (pte_swp_soft_dirty(pte))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_swp_uffd_wp(pte))
swp_pte = pte_swp_mkuffd_wp(swp_pte);
}
set_pte_at(mm, addr, ptep, swp_pte);
/*
* This is like regular unmap: we remove the rmap and
* drop page refcount. Page won't be freed, as we took
* a reference just above.
*/
page_remove_rmap(page, vma, false);
put_page(page);
if (pte_present(pte))
unmapped++;
} else {
put_page(page);
mpfn = 0;
}
next:
migrate->dst[migrate->npages] = 0;
migrate->src[migrate->npages++] = mpfn;
}
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(ptep - 1, ptl);
/* Only flush the TLB if we actually modified any entries */
if (unmapped)
flush_tlb_range(walk->vma, start, end);
return 0;
}
static const struct mm_walk_ops migrate_vma_walk_ops = {
.pmd_entry = migrate_vma_collect_pmd,
.pte_hole = migrate_vma_collect_hole,
};
/*
* migrate_vma_collect() - collect pages over a range of virtual addresses
* @migrate: migrate struct containing all migration information
*
* This will walk the CPU page table. For each virtual address backed by a
* valid page, it updates the src array and takes a reference on the page, in
* order to pin the page until we lock it and unmap it.
*/
static void migrate_vma_collect(struct migrate_vma *migrate)
{
struct mmu_notifier_range range;
/*
* Note that the pgmap_owner is passed to the mmu notifier callback so
* that the registered device driver can skip invalidating device
* private page mappings that won't be migrated.
*/
mmu_notifier_range_init_owner(&range, MMU_NOTIFY_MIGRATE, 0,
migrate->vma, migrate->vma->vm_mm, migrate->start, migrate->end,
migrate->pgmap_owner);
mmu_notifier_invalidate_range_start(&range);
walk_page_range(migrate->vma->vm_mm, migrate->start, migrate->end,
&migrate_vma_walk_ops, migrate);
mmu_notifier_invalidate_range_end(&range);
migrate->end = migrate->start + (migrate->npages << PAGE_SHIFT);
}
/*
* migrate_vma_check_page() - check if page is pinned or not
* @page: struct page to check
*
* Pinned pages cannot be migrated. This is the same test as in
* folio_migrate_mapping(), except that here we allow migration of a
* ZONE_DEVICE page.
*/
static bool migrate_vma_check_page(struct page *page)
{
/*
* One extra ref because caller holds an extra reference, either from
* isolate_lru_page() for a regular page, or migrate_vma_collect() for
* a device page.
*/
int extra = 1;
/*
* FIXME support THP (transparent huge page), it is bit more complex to
* check them than regular pages, because they can be mapped with a pmd
* or with a pte (split pte mapping).
*/
if (PageCompound(page))
return false;
/* Page from ZONE_DEVICE have one extra reference */
if (is_zone_device_page(page))
extra++;
/* For file back page */
if (page_mapping(page))
extra += 1 + page_has_private(page);
if ((page_count(page) - extra) > page_mapcount(page))
return false;
return true;
}
/*
* migrate_vma_unmap() - replace page mapping with special migration pte entry
* @migrate: migrate struct containing all migration information
*
* Isolate pages from the LRU and replace mappings (CPU page table pte) with a
* special migration pte entry and check if it has been pinned. Pinned pages are
* restored because we cannot migrate them.
*
* This is the last step before we call the device driver callback to allocate
* destination memory and copy contents of original page over to new page.
*/
static void migrate_vma_unmap(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
unsigned long i, restore = 0;
bool allow_drain = true;
lru_add_drain();
for (i = 0; i < npages; i++) {
struct page *page = migrate_pfn_to_page(migrate->src[i]);
if (!page)
continue;
/* ZONE_DEVICE pages are not on LRU */
if (!is_zone_device_page(page)) {
if (!PageLRU(page) && allow_drain) {
/* Drain CPU's pagevec */
lru_add_drain_all();
allow_drain = false;
}
if (isolate_lru_page(page)) {
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
migrate->cpages--;
restore++;
continue;
}
/* Drop the reference we took in collect */
put_page(page);
}
if (page_mapped(page))
try_to_migrate(page, 0);
if (page_mapped(page) || !migrate_vma_check_page(page)) {
if (!is_zone_device_page(page)) {
get_page(page);
putback_lru_page(page);
}
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
migrate->cpages--;
restore++;
continue;
}
}
for (i = 0; i < npages && restore; i++) {
struct page *page = migrate_pfn_to_page(migrate->src[i]);
if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
continue;
remove_migration_ptes(page, page, false);
migrate->src[i] = 0;
unlock_page(page);
put_page(page);
restore--;
}
}
/**
* migrate_vma_setup() - prepare to migrate a range of memory
* @args: contains the vma, start, and pfns arrays for the migration
*
* Returns: negative errno on failures, 0 when 0 or more pages were migrated
* without an error.
*
* Prepare to migrate a range of memory virtual address range by collecting all
* the pages backing each virtual address in the range, saving them inside the
* src array. Then lock those pages and unmap them. Once the pages are locked
* and unmapped, check whether each page is pinned or not. Pages that aren't
* pinned have the MIGRATE_PFN_MIGRATE flag set (by this function) in the
* corresponding src array entry. Then restores any pages that are pinned, by
* remapping and unlocking those pages.
*
* The caller should then allocate destination memory and copy source memory to
* it for all those entries (ie with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
* flag set). Once these are allocated and copied, the caller must update each
* corresponding entry in the dst array with the pfn value of the destination
* page and with MIGRATE_PFN_VALID. Destination pages must be locked via
* lock_page().
*
* Note that the caller does not have to migrate all the pages that are marked
* with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration from
* device memory to system memory. If the caller cannot migrate a device page
* back to system memory, then it must return VM_FAULT_SIGBUS, which has severe
* consequences for the userspace process, so it must be avoided if at all
* possible.
*
* For empty entries inside CPU page table (pte_none() or pmd_none() is true) we
* do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array thus
* allowing the caller to allocate device memory for those unbacked virtual
* addresses. For this the caller simply has to allocate device memory and
* properly set the destination entry like for regular migration. Note that
* this can still fail, and thus inside the device driver you must check if the
* migration was successful for those entries after calling migrate_vma_pages(),
* just like for regular migration.
*
* After that, the callers must call migrate_vma_pages() to go over each entry
* in the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
* set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
* then migrate_vma_pages() to migrate struct page information from the source
* struct page to the destination struct page. If it fails to migrate the
* struct page information, then it clears the MIGRATE_PFN_MIGRATE flag in the
* src array.
*
* At this point all successfully migrated pages have an entry in the src
* array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
* array entry with MIGRATE_PFN_VALID flag set.
*
* Once migrate_vma_pages() returns the caller may inspect which pages were
* successfully migrated, and which were not. Successfully migrated pages will
* have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
*
* It is safe to update device page table after migrate_vma_pages() because
* both destination and source page are still locked, and the mmap_lock is held
* in read mode (hence no one can unmap the range being migrated).
*
* Once the caller is done cleaning up things and updating its page table (if it
* chose to do so, this is not an obligation) it finally calls
* migrate_vma_finalize() to update the CPU page table to point to new pages
* for successfully migrated pages or otherwise restore the CPU page table to
* point to the original source pages.
*/
int migrate_vma_setup(struct migrate_vma *args)
{
long nr_pages = (args->end - args->start) >> PAGE_SHIFT;
args->start &= PAGE_MASK;
args->end &= PAGE_MASK;
if (!args->vma || is_vm_hugetlb_page(args->vma) ||
(args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
return -EINVAL;
if (nr_pages <= 0)
return -EINVAL;
if (args->start < args->vma->vm_start ||
args->start >= args->vma->vm_end)
return -EINVAL;
if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
return -EINVAL;
if (!args->src || !args->dst)
return -EINVAL;
memset(args->src, 0, sizeof(*args->src) * nr_pages);
args->cpages = 0;
args->npages = 0;
migrate_vma_collect(args);
if (args->cpages)
migrate_vma_unmap(args);
/*
* At this point pages are locked and unmapped, and thus they have
* stable content and can safely be copied to destination memory that
* is allocated by the drivers.
*/
return 0;
}
EXPORT_SYMBOL(migrate_vma_setup);
/*
* This code closely matches the code in:
* __handle_mm_fault()
* handle_pte_fault()
* do_anonymous_page()
* to map in an anonymous zero page but the struct page will be a ZONE_DEVICE
* private page.
*/
static void migrate_vma_insert_page(struct migrate_vma *migrate,
unsigned long addr,
struct page *page,
unsigned long *src)
{
struct vm_area_struct *vma = migrate->vma;
struct mm_struct *mm = vma->vm_mm;
bool flush = false;
spinlock_t *ptl;
pte_t entry;
pgd_t *pgdp;
p4d_t *p4dp;
pud_t *pudp;
pmd_t *pmdp;
pte_t *ptep;
/* Only allow populating anonymous memory */
if (!vma_is_anonymous(vma))
goto abort;
pgdp = pgd_offset(mm, addr);
p4dp = p4d_alloc(mm, pgdp, addr);
if (!p4dp)
goto abort;
pudp = pud_alloc(mm, p4dp, addr);
if (!pudp)
goto abort;
pmdp = pmd_alloc(mm, pudp, addr);
if (!pmdp)
goto abort;
if (pmd_trans_huge(*pmdp) || pmd_devmap(*pmdp))
goto abort;
/*
* Use pte_alloc() instead of pte_alloc_map(). We can't run
* pte_offset_map() on pmds where a huge pmd might be created
* from a different thread.
*
* pte_alloc_map() is safe to use under mmap_write_lock(mm) or when
* parallel threads are excluded by other means.
*
* Here we only have mmap_read_lock(mm).
*/
if (pte_alloc(mm, pmdp))
goto abort;
/* See the comment in pte_alloc_one_map() */
if (unlikely(pmd_trans_unstable(pmdp)))
goto abort;
if (unlikely(anon_vma_prepare(vma)))
goto abort;
if (mem_cgroup_charge(page_folio(page), vma->vm_mm, GFP_KERNEL))
goto abort;
/*
* The memory barrier inside __SetPageUptodate makes sure that
* preceding stores to the page contents become visible before
* the set_pte_at() write.
*/
__SetPageUptodate(page);
if (is_device_private_page(page)) {
swp_entry_t swp_entry;
if (vma->vm_flags & VM_WRITE)
swp_entry = make_writable_device_private_entry(
page_to_pfn(page));
else
swp_entry = make_readable_device_private_entry(
page_to_pfn(page));
entry = swp_entry_to_pte(swp_entry);
} else {
/*
* For now we only support migrating to un-addressable device
* memory.
*/
if (is_zone_device_page(page)) {
pr_warn_once("Unsupported ZONE_DEVICE page type.\n");
goto abort;
}
entry = mk_pte(page, vma->vm_page_prot);
if (vma->vm_flags & VM_WRITE)
entry = pte_mkwrite(pte_mkdirty(entry));
}
ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
if (check_stable_address_space(mm))
goto unlock_abort;
if (pte_present(*ptep)) {
unsigned long pfn = pte_pfn(*ptep);
if (!is_zero_pfn(pfn))
goto unlock_abort;
flush = true;
} else if (!pte_none(*ptep))
goto unlock_abort;
/*
* Check for userfaultfd but do not deliver the fault. Instead,
* just back off.
*/
if (userfaultfd_missing(vma))
goto unlock_abort;
inc_mm_counter(mm, MM_ANONPAGES);
page_add_new_anon_rmap(page, vma, addr, false);
if (!is_zone_device_page(page))
lru_cache_add_inactive_or_unevictable(page, vma);
get_page(page);
if (flush) {
flush_cache_page(vma, addr, pte_pfn(*ptep));
ptep_clear_flush_notify(vma, addr, ptep);
set_pte_at_notify(mm, addr, ptep, entry);
update_mmu_cache(vma, addr, ptep);
} else {
/* No need to invalidate - it was non-present before */
set_pte_at(mm, addr, ptep, entry);
update_mmu_cache(vma, addr, ptep);
}
pte_unmap_unlock(ptep, ptl);
*src = MIGRATE_PFN_MIGRATE;
return;
unlock_abort:
pte_unmap_unlock(ptep, ptl);
abort:
*src &= ~MIGRATE_PFN_MIGRATE;
}
/**
* migrate_vma_pages() - migrate meta-data from src page to dst page
* @migrate: migrate struct containing all migration information
*
* This migrates struct page meta-data from source struct page to destination
* struct page. This effectively finishes the migration from source page to the
* destination page.
*/
void migrate_vma_pages(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
const unsigned long start = migrate->start;
struct mmu_notifier_range range;
unsigned long addr, i;
bool notified = false;
for (i = 0, addr = start; i < npages; addr += PAGE_SIZE, i++) {
struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
struct page *page = migrate_pfn_to_page(migrate->src[i]);
struct address_space *mapping;
int r;
if (!newpage) {
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
continue;
}
if (!page) {
if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE))
continue;
if (!notified) {
notified = true;
mmu_notifier_range_init_owner(&range,
MMU_NOTIFY_MIGRATE, 0, migrate->vma,
migrate->vma->vm_mm, addr, migrate->end,
migrate->pgmap_owner);
mmu_notifier_invalidate_range_start(&range);
}
migrate_vma_insert_page(migrate, addr, newpage,
&migrate->src[i]);
continue;
}
mapping = page_mapping(page);
if (is_device_private_page(newpage)) {
/*
* For now only support private anonymous when migrating
* to un-addressable device memory.
*/
if (mapping) {
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
continue;
}
} else if (is_zone_device_page(newpage)) {
/*
* Other types of ZONE_DEVICE page are not supported.
*/
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
continue;
}
r = migrate_page(mapping, newpage, page, MIGRATE_SYNC_NO_COPY);
if (r != MIGRATEPAGE_SUCCESS)
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
}
/*
* No need to double call mmu_notifier->invalidate_range() callback as
* the above ptep_clear_flush_notify() inside migrate_vma_insert_page()
* did already call it.
*/
if (notified)
mmu_notifier_invalidate_range_only_end(&range);
}
EXPORT_SYMBOL(migrate_vma_pages);
/**
* migrate_vma_finalize() - restore CPU page table entry
* @migrate: migrate struct containing all migration information
*
* This replaces the special migration pte entry with either a mapping to the
* new page if migration was successful for that page, or to the original page
* otherwise.
*
* This also unlocks the pages and puts them back on the lru, or drops the extra
* refcount, for device pages.
*/
void migrate_vma_finalize(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
unsigned long i;
for (i = 0; i < npages; i++) {
struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
struct page *page = migrate_pfn_to_page(migrate->src[i]);
if (!page) {
if (newpage) {
unlock_page(newpage);
put_page(newpage);
}
continue;
}
if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
if (newpage) {
unlock_page(newpage);
put_page(newpage);
}
newpage = page;
}
remove_migration_ptes(page, newpage, false);
unlock_page(page);
if (is_zone_device_page(page))
put_page(page);
else
putback_lru_page(page);
if (newpage != page) {
unlock_page(newpage);
if (is_zone_device_page(newpage))
put_page(newpage);
else
putback_lru_page(newpage);
}
}
}
EXPORT_SYMBOL(migrate_vma_finalize);
#endif /* CONFIG_DEVICE_PRIVATE */
/*
* node_demotion[] example:
*

766
mm/migrate_device.c Normal file
View File

@ -0,0 +1,766 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Device Memory Migration functionality.
*
* Originally written by Jérôme Glisse.
*/
#include <linux/export.h>
#include <linux/memremap.h>
#include <linux/migrate.h>
#include <linux/mm_inline.h>
#include <linux/mmu_notifier.h>
#include <linux/oom.h>
#include <linux/pagewalk.h>
#include <linux/rmap.h>
#include <linux/swapops.h>
#include <asm/tlbflush.h>
#include "internal.h"
static int migrate_vma_collect_skip(unsigned long start,
unsigned long end,
struct mm_walk *walk)
{
struct migrate_vma *migrate = walk->private;
unsigned long addr;
for (addr = start; addr < end; addr += PAGE_SIZE) {
migrate->dst[migrate->npages] = 0;
migrate->src[migrate->npages++] = 0;
}
return 0;
}
static int migrate_vma_collect_hole(unsigned long start,
unsigned long end,
__always_unused int depth,
struct mm_walk *walk)
{
struct migrate_vma *migrate = walk->private;
unsigned long addr;
/* Only allow populating anonymous memory. */
if (!vma_is_anonymous(walk->vma))
return migrate_vma_collect_skip(start, end, walk);
for (addr = start; addr < end; addr += PAGE_SIZE) {
migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
migrate->dst[migrate->npages] = 0;
migrate->npages++;
migrate->cpages++;
}
return 0;
}
static int migrate_vma_collect_pmd(pmd_t *pmdp,
unsigned long start,
unsigned long end,
struct mm_walk *walk)
{
struct migrate_vma *migrate = walk->private;
struct vm_area_struct *vma = walk->vma;
struct mm_struct *mm = vma->vm_mm;
unsigned long addr = start, unmapped = 0;
spinlock_t *ptl;
pte_t *ptep;
again:
if (pmd_none(*pmdp))
return migrate_vma_collect_hole(start, end, -1, walk);
if (pmd_trans_huge(*pmdp)) {
struct page *page;
ptl = pmd_lock(mm, pmdp);
if (unlikely(!pmd_trans_huge(*pmdp))) {
spin_unlock(ptl);
goto again;
}
page = pmd_page(*pmdp);
if (is_huge_zero_page(page)) {
spin_unlock(ptl);
split_huge_pmd(vma, pmdp, addr);
if (pmd_trans_unstable(pmdp))
return migrate_vma_collect_skip(start, end,
walk);
} else {
int ret;
get_page(page);
spin_unlock(ptl);
if (unlikely(!trylock_page(page)))
return migrate_vma_collect_skip(start, end,
walk);
ret = split_huge_page(page);
unlock_page(page);
put_page(page);
if (ret)
return migrate_vma_collect_skip(start, end,
walk);
if (pmd_none(*pmdp))
return migrate_vma_collect_hole(start, end, -1,
walk);
}
}
if (unlikely(pmd_bad(*pmdp)))
return migrate_vma_collect_skip(start, end, walk);
ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
arch_enter_lazy_mmu_mode();
for (; addr < end; addr += PAGE_SIZE, ptep++) {
unsigned long mpfn = 0, pfn;
struct page *page;
swp_entry_t entry;
pte_t pte;
pte = *ptep;
if (pte_none(pte)) {
if (vma_is_anonymous(vma)) {
mpfn = MIGRATE_PFN_MIGRATE;
migrate->cpages++;
}
goto next;
}
if (!pte_present(pte)) {
/*
* Only care about unaddressable device page special
* page table entry. Other special swap entries are not
* migratable, and we ignore regular swapped page.
*/
entry = pte_to_swp_entry(pte);
if (!is_device_private_entry(entry))
goto next;
page = pfn_swap_entry_to_page(entry);
if (!(migrate->flags &
MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
page->pgmap->owner != migrate->pgmap_owner)
goto next;
mpfn = migrate_pfn(page_to_pfn(page)) |
MIGRATE_PFN_MIGRATE;
if (is_writable_device_private_entry(entry))
mpfn |= MIGRATE_PFN_WRITE;
} else {
if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
goto next;
pfn = pte_pfn(pte);
if (is_zero_pfn(pfn)) {
mpfn = MIGRATE_PFN_MIGRATE;
migrate->cpages++;
goto next;
}
page = vm_normal_page(migrate->vma, addr, pte);
mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
}
/* FIXME support THP */
if (!page || !page->mapping || PageTransCompound(page)) {
mpfn = 0;
goto next;
}
/*
* By getting a reference on the page we pin it and that blocks
* any kind of migration. Side effect is that it "freezes" the
* pte.
*
* We drop this reference after isolating the page from the lru
* for non device page (device page are not on the lru and thus
* can't be dropped from it).
*/
get_page(page);
/*
* Optimize for the common case where page is only mapped once
* in one process. If we can lock the page, then we can safely
* set up a special migration page table entry now.
*/
if (trylock_page(page)) {
pte_t swp_pte;
migrate->cpages++;
ptep_get_and_clear(mm, addr, ptep);
/* Setup special migration page table entry */
if (mpfn & MIGRATE_PFN_WRITE)
entry = make_writable_migration_entry(
page_to_pfn(page));
else
entry = make_readable_migration_entry(
page_to_pfn(page));
swp_pte = swp_entry_to_pte(entry);
if (pte_present(pte)) {
if (pte_soft_dirty(pte))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_uffd_wp(pte))
swp_pte = pte_swp_mkuffd_wp(swp_pte);
} else {
if (pte_swp_soft_dirty(pte))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_swp_uffd_wp(pte))
swp_pte = pte_swp_mkuffd_wp(swp_pte);
}
set_pte_at(mm, addr, ptep, swp_pte);
/*
* This is like regular unmap: we remove the rmap and
* drop page refcount. Page won't be freed, as we took
* a reference just above.
*/
page_remove_rmap(page, vma, false);
put_page(page);
if (pte_present(pte))
unmapped++;
} else {
put_page(page);
mpfn = 0;
}
next:
migrate->dst[migrate->npages] = 0;
migrate->src[migrate->npages++] = mpfn;
}
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(ptep - 1, ptl);
/* Only flush the TLB if we actually modified any entries */
if (unmapped)
flush_tlb_range(walk->vma, start, end);
return 0;
}
static const struct mm_walk_ops migrate_vma_walk_ops = {
.pmd_entry = migrate_vma_collect_pmd,
.pte_hole = migrate_vma_collect_hole,
};
/*
* migrate_vma_collect() - collect pages over a range of virtual addresses
* @migrate: migrate struct containing all migration information
*
* This will walk the CPU page table. For each virtual address backed by a
* valid page, it updates the src array and takes a reference on the page, in
* order to pin the page until we lock it and unmap it.
*/
static void migrate_vma_collect(struct migrate_vma *migrate)
{
struct mmu_notifier_range range;
/*
* Note that the pgmap_owner is passed to the mmu notifier callback so
* that the registered device driver can skip invalidating device
* private page mappings that won't be migrated.
*/
mmu_notifier_range_init_owner(&range, MMU_NOTIFY_MIGRATE, 0,
migrate->vma, migrate->vma->vm_mm, migrate->start, migrate->end,
migrate->pgmap_owner);
mmu_notifier_invalidate_range_start(&range);
walk_page_range(migrate->vma->vm_mm, migrate->start, migrate->end,
&migrate_vma_walk_ops, migrate);
mmu_notifier_invalidate_range_end(&range);
migrate->end = migrate->start + (migrate->npages << PAGE_SHIFT);
}
/*
* migrate_vma_check_page() - check if page is pinned or not
* @page: struct page to check
*
* Pinned pages cannot be migrated. This is the same test as in
* folio_migrate_mapping(), except that here we allow migration of a
* ZONE_DEVICE page.
*/
static bool migrate_vma_check_page(struct page *page)
{
/*
* One extra ref because caller holds an extra reference, either from
* isolate_lru_page() for a regular page, or migrate_vma_collect() for
* a device page.
*/
int extra = 1;
/*
* FIXME support THP (transparent huge page), it is bit more complex to
* check them than regular pages, because they can be mapped with a pmd
* or with a pte (split pte mapping).
*/
if (PageCompound(page))
return false;
/* Page from ZONE_DEVICE have one extra reference */
if (is_zone_device_page(page))
extra++;
/* For file back page */
if (page_mapping(page))
extra += 1 + page_has_private(page);
if ((page_count(page) - extra) > page_mapcount(page))
return false;
return true;
}
/*
* migrate_vma_unmap() - replace page mapping with special migration pte entry
* @migrate: migrate struct containing all migration information
*
* Isolate pages from the LRU and replace mappings (CPU page table pte) with a
* special migration pte entry and check if it has been pinned. Pinned pages are
* restored because we cannot migrate them.
*
* This is the last step before we call the device driver callback to allocate
* destination memory and copy contents of original page over to new page.
*/
static void migrate_vma_unmap(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
unsigned long i, restore = 0;
bool allow_drain = true;
lru_add_drain();
for (i = 0; i < npages; i++) {
struct page *page = migrate_pfn_to_page(migrate->src[i]);
if (!page)
continue;
/* ZONE_DEVICE pages are not on LRU */
if (!is_zone_device_page(page)) {
if (!PageLRU(page) && allow_drain) {
/* Drain CPU's pagevec */
lru_add_drain_all();
allow_drain = false;
}
if (isolate_lru_page(page)) {
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
migrate->cpages--;
restore++;
continue;
}
/* Drop the reference we took in collect */
put_page(page);
}
if (page_mapped(page))
try_to_migrate(page, 0);
if (page_mapped(page) || !migrate_vma_check_page(page)) {
if (!is_zone_device_page(page)) {
get_page(page);
putback_lru_page(page);
}
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
migrate->cpages--;
restore++;
continue;
}
}
for (i = 0; i < npages && restore; i++) {
struct page *page = migrate_pfn_to_page(migrate->src[i]);
if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
continue;
remove_migration_ptes(page, page, false);
migrate->src[i] = 0;
unlock_page(page);
put_page(page);
restore--;
}
}
/**
* migrate_vma_setup() - prepare to migrate a range of memory
* @args: contains the vma, start, and pfns arrays for the migration
*
* Returns: negative errno on failures, 0 when 0 or more pages were migrated
* without an error.
*
* Prepare to migrate a range of memory virtual address range by collecting all
* the pages backing each virtual address in the range, saving them inside the
* src array. Then lock those pages and unmap them. Once the pages are locked
* and unmapped, check whether each page is pinned or not. Pages that aren't
* pinned have the MIGRATE_PFN_MIGRATE flag set (by this function) in the
* corresponding src array entry. Then restores any pages that are pinned, by
* remapping and unlocking those pages.
*
* The caller should then allocate destination memory and copy source memory to
* it for all those entries (ie with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
* flag set). Once these are allocated and copied, the caller must update each
* corresponding entry in the dst array with the pfn value of the destination
* page and with MIGRATE_PFN_VALID. Destination pages must be locked via
* lock_page().
*
* Note that the caller does not have to migrate all the pages that are marked
* with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration from
* device memory to system memory. If the caller cannot migrate a device page
* back to system memory, then it must return VM_FAULT_SIGBUS, which has severe
* consequences for the userspace process, so it must be avoided if at all
* possible.
*
* For empty entries inside CPU page table (pte_none() or pmd_none() is true) we
* do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array thus
* allowing the caller to allocate device memory for those unbacked virtual
* addresses. For this the caller simply has to allocate device memory and
* properly set the destination entry like for regular migration. Note that
* this can still fail, and thus inside the device driver you must check if the
* migration was successful for those entries after calling migrate_vma_pages(),
* just like for regular migration.
*
* After that, the callers must call migrate_vma_pages() to go over each entry
* in the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
* set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
* then migrate_vma_pages() to migrate struct page information from the source
* struct page to the destination struct page. If it fails to migrate the
* struct page information, then it clears the MIGRATE_PFN_MIGRATE flag in the
* src array.
*
* At this point all successfully migrated pages have an entry in the src
* array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
* array entry with MIGRATE_PFN_VALID flag set.
*
* Once migrate_vma_pages() returns the caller may inspect which pages were
* successfully migrated, and which were not. Successfully migrated pages will
* have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
*
* It is safe to update device page table after migrate_vma_pages() because
* both destination and source page are still locked, and the mmap_lock is held
* in read mode (hence no one can unmap the range being migrated).
*
* Once the caller is done cleaning up things and updating its page table (if it
* chose to do so, this is not an obligation) it finally calls
* migrate_vma_finalize() to update the CPU page table to point to new pages
* for successfully migrated pages or otherwise restore the CPU page table to
* point to the original source pages.
*/
int migrate_vma_setup(struct migrate_vma *args)
{
long nr_pages = (args->end - args->start) >> PAGE_SHIFT;
args->start &= PAGE_MASK;
args->end &= PAGE_MASK;
if (!args->vma || is_vm_hugetlb_page(args->vma) ||
(args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
return -EINVAL;
if (nr_pages <= 0)
return -EINVAL;
if (args->start < args->vma->vm_start ||
args->start >= args->vma->vm_end)
return -EINVAL;
if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
return -EINVAL;
if (!args->src || !args->dst)
return -EINVAL;
memset(args->src, 0, sizeof(*args->src) * nr_pages);
args->cpages = 0;
args->npages = 0;
migrate_vma_collect(args);
if (args->cpages)
migrate_vma_unmap(args);
/*
* At this point pages are locked and unmapped, and thus they have
* stable content and can safely be copied to destination memory that
* is allocated by the drivers.
*/
return 0;
}
EXPORT_SYMBOL(migrate_vma_setup);
/*
* This code closely matches the code in:
* __handle_mm_fault()
* handle_pte_fault()
* do_anonymous_page()
* to map in an anonymous zero page but the struct page will be a ZONE_DEVICE
* private page.
*/
static void migrate_vma_insert_page(struct migrate_vma *migrate,
unsigned long addr,
struct page *page,
unsigned long *src)
{
struct vm_area_struct *vma = migrate->vma;
struct mm_struct *mm = vma->vm_mm;
bool flush = false;
spinlock_t *ptl;
pte_t entry;
pgd_t *pgdp;
p4d_t *p4dp;
pud_t *pudp;
pmd_t *pmdp;
pte_t *ptep;
/* Only allow populating anonymous memory */
if (!vma_is_anonymous(vma))
goto abort;
pgdp = pgd_offset(mm, addr);
p4dp = p4d_alloc(mm, pgdp, addr);
if (!p4dp)
goto abort;
pudp = pud_alloc(mm, p4dp, addr);
if (!pudp)
goto abort;
pmdp = pmd_alloc(mm, pudp, addr);
if (!pmdp)
goto abort;
if (pmd_trans_huge(*pmdp) || pmd_devmap(*pmdp))
goto abort;
/*
* Use pte_alloc() instead of pte_alloc_map(). We can't run
* pte_offset_map() on pmds where a huge pmd might be created
* from a different thread.
*
* pte_alloc_map() is safe to use under mmap_write_lock(mm) or when
* parallel threads are excluded by other means.
*
* Here we only have mmap_read_lock(mm).
*/
if (pte_alloc(mm, pmdp))
goto abort;
/* See the comment in pte_alloc_one_map() */
if (unlikely(pmd_trans_unstable(pmdp)))
goto abort;
if (unlikely(anon_vma_prepare(vma)))
goto abort;
if (mem_cgroup_charge(page_folio(page), vma->vm_mm, GFP_KERNEL))
goto abort;
/*
* The memory barrier inside __SetPageUptodate makes sure that
* preceding stores to the page contents become visible before
* the set_pte_at() write.
*/
__SetPageUptodate(page);
if (is_device_private_page(page)) {
swp_entry_t swp_entry;
if (vma->vm_flags & VM_WRITE)
swp_entry = make_writable_device_private_entry(
page_to_pfn(page));
else
swp_entry = make_readable_device_private_entry(
page_to_pfn(page));
entry = swp_entry_to_pte(swp_entry);
} else {
/*
* For now we only support migrating to un-addressable device
* memory.
*/
if (is_zone_device_page(page)) {
pr_warn_once("Unsupported ZONE_DEVICE page type.\n");
goto abort;
}
entry = mk_pte(page, vma->vm_page_prot);
if (vma->vm_flags & VM_WRITE)
entry = pte_mkwrite(pte_mkdirty(entry));
}
ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
if (check_stable_address_space(mm))
goto unlock_abort;
if (pte_present(*ptep)) {
unsigned long pfn = pte_pfn(*ptep);
if (!is_zero_pfn(pfn))
goto unlock_abort;
flush = true;
} else if (!pte_none(*ptep))
goto unlock_abort;
/*
* Check for userfaultfd but do not deliver the fault. Instead,
* just back off.
*/
if (userfaultfd_missing(vma))
goto unlock_abort;
inc_mm_counter(mm, MM_ANONPAGES);
page_add_new_anon_rmap(page, vma, addr, false);
if (!is_zone_device_page(page))
lru_cache_add_inactive_or_unevictable(page, vma);
get_page(page);
if (flush) {
flush_cache_page(vma, addr, pte_pfn(*ptep));
ptep_clear_flush_notify(vma, addr, ptep);
set_pte_at_notify(mm, addr, ptep, entry);
update_mmu_cache(vma, addr, ptep);
} else {
/* No need to invalidate - it was non-present before */
set_pte_at(mm, addr, ptep, entry);
update_mmu_cache(vma, addr, ptep);
}
pte_unmap_unlock(ptep, ptl);
*src = MIGRATE_PFN_MIGRATE;
return;
unlock_abort:
pte_unmap_unlock(ptep, ptl);
abort:
*src &= ~MIGRATE_PFN_MIGRATE;
}
/**
* migrate_vma_pages() - migrate meta-data from src page to dst page
* @migrate: migrate struct containing all migration information
*
* This migrates struct page meta-data from source struct page to destination
* struct page. This effectively finishes the migration from source page to the
* destination page.
*/
void migrate_vma_pages(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
const unsigned long start = migrate->start;
struct mmu_notifier_range range;
unsigned long addr, i;
bool notified = false;
for (i = 0, addr = start; i < npages; addr += PAGE_SIZE, i++) {
struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
struct page *page = migrate_pfn_to_page(migrate->src[i]);
struct address_space *mapping;
int r;
if (!newpage) {
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
continue;
}
if (!page) {
if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE))
continue;
if (!notified) {
notified = true;
mmu_notifier_range_init_owner(&range,
MMU_NOTIFY_MIGRATE, 0, migrate->vma,
migrate->vma->vm_mm, addr, migrate->end,
migrate->pgmap_owner);
mmu_notifier_invalidate_range_start(&range);
}
migrate_vma_insert_page(migrate, addr, newpage,
&migrate->src[i]);
continue;
}
mapping = page_mapping(page);
if (is_device_private_page(newpage)) {
/*
* For now only support private anonymous when migrating
* to un-addressable device memory.
*/
if (mapping) {
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
continue;
}
} else if (is_zone_device_page(newpage)) {
/*
* Other types of ZONE_DEVICE page are not supported.
*/
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
continue;
}
r = migrate_page(mapping, newpage, page, MIGRATE_SYNC_NO_COPY);
if (r != MIGRATEPAGE_SUCCESS)
migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
}
/*
* No need to double call mmu_notifier->invalidate_range() callback as
* the above ptep_clear_flush_notify() inside migrate_vma_insert_page()
* did already call it.
*/
if (notified)
mmu_notifier_invalidate_range_only_end(&range);
}
EXPORT_SYMBOL(migrate_vma_pages);
/**
* migrate_vma_finalize() - restore CPU page table entry
* @migrate: migrate struct containing all migration information
*
* This replaces the special migration pte entry with either a mapping to the
* new page if migration was successful for that page, or to the original page
* otherwise.
*
* This also unlocks the pages and puts them back on the lru, or drops the extra
* refcount, for device pages.
*/
void migrate_vma_finalize(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
unsigned long i;
for (i = 0; i < npages; i++) {
struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
struct page *page = migrate_pfn_to_page(migrate->src[i]);
if (!page) {
if (newpage) {
unlock_page(newpage);
put_page(newpage);
}
continue;
}
if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
if (newpage) {
unlock_page(newpage);
put_page(newpage);
}
newpage = page;
}
remove_migration_ptes(page, newpage, false);
unlock_page(page);
if (is_zone_device_page(page))
put_page(page);
else
putback_lru_page(page);
if (newpage != page) {
unlock_page(newpage);
if (is_zone_device_page(newpage))
put_page(newpage);
else
putback_lru_page(newpage);
}
}
}
EXPORT_SYMBOL(migrate_vma_finalize);