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hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization 

While looking at BUGs associated with invalid huge page map counts, it was
discovered and observed that a huge pte pointer could become 'invalid' and
point to another task's page table.  Consider the following:

A task takes a page fault on a shared hugetlbfs file and calls
huge_pte_alloc to get a ptep.  Suppose the returned ptep points to a
shared pmd.

Now, another task truncates the hugetlbfs file.  As part of truncation, it
unmaps everyone who has the file mapped.  If the range being truncated is
covered by a shared pmd, huge_pmd_unshare will be called.  For all but the
last user of the shared pmd, huge_pmd_unshare will clear the pud pointing
to the pmd.  If the task in the middle of the page fault is not the last
user, the ptep returned by huge_pte_alloc now points to another task's
page table or worse.  This leads to bad things such as incorrect page
map/reference counts or invalid memory references.

To fix, expand the use of i_mmap_rwsem as follows:

- i_mmap_rwsem is held in read mode whenever huge_pmd_share is called.
  huge_pmd_share is only called via huge_pte_alloc, so callers of
  huge_pte_alloc take i_mmap_rwsem before calling.  In addition, callers
  of huge_pte_alloc continue to hold the semaphore until finished with the
  ptep.

- i_mmap_rwsem is held in write mode whenever huge_pmd_unshare is
  called.

[mike.kravetz@oracle.com: add explicit check for mapping != null]
Link: http://lkml.kernel.org/r/20181218223557.5202-2-mike.kravetz@oracle.com
Fixes: 39dde65c99 ("shared page table for hugetlb page")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Prakash Sangappa <prakash.sangappa@oracle.com>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mike Kravetz 2018-12-28 00:39:38 -08:00 committed by Linus Torvalds
parent 1ecc07fd0a
commit b43a999005
5 changed files with 88 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

64
mm/hugetlb.c
View File

@ -3238,6 +3238,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
struct page *ptepage;
unsigned long addr;
int cow;
struct address_space *mapping = vma->vm_file->f_mapping;
struct hstate *h = hstate_vma(vma);
unsigned long sz = huge_page_size(h);
struct mmu_notifier_range range;
@ -3249,13 +3250,23 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
mmu_notifier_range_init(&range, src, vma->vm_start,
vma->vm_end);
mmu_notifier_invalidate_range_start(&range);
} else {
/*
* For shared mappings i_mmap_rwsem must be held to call
* huge_pte_alloc, otherwise the returned ptep could go
* away if part of a shared pmd and another thread calls
* huge_pmd_unshare.
*/
i_mmap_lock_read(mapping);
}
for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) {
spinlock_t *src_ptl, *dst_ptl;
src_pte = huge_pte_offset(src, addr, sz);
if (!src_pte)
continue;
dst_pte = huge_pte_alloc(dst, addr, sz);
if (!dst_pte) {
ret = -ENOMEM;
@ -3326,6 +3337,8 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
if (cow)
mmu_notifier_invalidate_range_end(&range);
else
i_mmap_unlock_read(mapping);
return ret;
}
@ -3771,14 +3784,18 @@ retry:
};
/*
* hugetlb_fault_mutex must be dropped before
* handling userfault. Reacquire after handling
* fault to make calling code simpler.
* hugetlb_fault_mutex and i_mmap_rwsem must be
* dropped before handling userfault. Reacquire
* after handling fault to make calling code simpler.
*/
hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping,
idx, haddr);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
i_mmap_unlock_read(mapping);
ret = handle_userfault(&vmf, VM_UFFD_MISSING);
i_mmap_lock_read(mapping);
mutex_lock(&hugetlb_fault_mutex_table[hash]);
goto out;
}
@ -3926,6 +3943,11 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
if (ptep) {
/*
* Since we hold no locks, ptep could be stale. That is
* OK as we are only making decisions based on content and
* not actually modifying content here.
*/
entry = huge_ptep_get(ptep);
if (unlikely(is_hugetlb_entry_migration(entry))) {
migration_entry_wait_huge(vma, mm, ptep);
@ -3933,20 +3955,31 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
return VM_FAULT_HWPOISON_LARGE |
VM_FAULT_SET_HINDEX(hstate_index(h));
} else {
ptep = huge_pte_alloc(mm, haddr, huge_page_size(h));
if (!ptep)
return VM_FAULT_OOM;
}
/*
* Acquire i_mmap_rwsem before calling huge_pte_alloc and hold
* until finished with ptep. This prevents huge_pmd_unshare from
* being called elsewhere and making the ptep no longer valid.
*
* ptep could have already be assigned via huge_pte_offset. That
* is OK, as huge_pte_alloc will return the same value unless
* something changed.
*/
mapping = vma->vm_file->f_mapping;
idx = vma_hugecache_offset(h, vma, haddr);
i_mmap_lock_read(mapping);
ptep = huge_pte_alloc(mm, haddr, huge_page_size(h));
if (!ptep) {
i_mmap_unlock_read(mapping);
return VM_FAULT_OOM;
}
/*
* Serialize hugepage allocation and instantiation, so that we don't
* get spurious allocation failures if two CPUs race to instantiate
* the same page in the page cache.
*/
idx = vma_hugecache_offset(h, vma, haddr);
hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping, idx, haddr);
mutex_lock(&hugetlb_fault_mutex_table[hash]);
@ -4034,6 +4067,7 @@ out_ptl:
}
out_mutex:
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
i_mmap_unlock_read(mapping);
/*
* Generally it's safe to hold refcount during waiting page lock. But
* here we just wait to defer the next page fault to avoid busy loop and
@ -4638,10 +4672,12 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
* Search for a shareable pmd page for hugetlb. In any case calls pmd_alloc()
* and returns the corresponding pte. While this is not necessary for the
* !shared pmd case because we can allocate the pmd later as well, it makes the
* code much cleaner. pmd allocation is essential for the shared case because
* pud has to be populated inside the same i_mmap_rwsem section - otherwise
* racing tasks could either miss the sharing (see huge_pte_offset) or select a
* bad pmd for sharing.
* code much cleaner.
*
* This routine must be called with i_mmap_rwsem held in at least read mode.
* For hugetlbfs, this prevents removal of any page table entries associated
* with the address space. This is important as we are setting up sharing
* based on existing page table entries (mappings).
*/
pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
{
@ -4658,7 +4694,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
if (!vma_shareable(vma, addr))
return (pte_t *)pmd_alloc(mm, pud, addr);
i_mmap_lock_write(mapping);
vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) {
if (svma == vma)
continue;
@ -4688,7 +4723,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
spin_unlock(ptl);
out:
pte = (pte_t *)pmd_alloc(mm, pud, addr);
i_mmap_unlock_write(mapping);
return pte;
}
@ -4699,7 +4733,7 @@ out:
* indicated by page_count > 1, unmap is achieved by clearing pud and
* decrementing the ref count. If count == 1, the pte page is not shared.
*
* called with page table lock held.
* Called with page table lock held and i_mmap_rwsem held in write mode.
*
* returns: 1 successfully unmapped a shared pte page
* 0 the underlying pte page is not shared, or it is the last user

14
mm/memory-failure.c
View File

@ -966,7 +966,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
enum ttu_flags ttu = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
struct address_space *mapping;
LIST_HEAD(tokill);
bool unmap_success;
bool unmap_success = true;
int kill = 1, forcekill;
struct page *hpage = *hpagep;
bool mlocked = PageMlocked(hpage);
@ -1028,7 +1028,19 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
if (kill)
collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
if (!PageHuge(hpage)) {
unmap_success = try_to_unmap(hpage, ttu);
} else if (mapping) {
/*
* For hugetlb pages, try_to_unmap could potentially call
* huge_pmd_unshare. Because of this, take semaphore in
* write mode here and set TTU_RMAP_LOCKED to indicate we
* have taken the lock at this higer level.
*/
i_mmap_lock_write(mapping);
unmap_success = try_to_unmap(hpage, ttu|TTU_RMAP_LOCKED);
i_mmap_unlock_write(mapping);
}
if (!unmap_success)
pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",
pfn, page_mapcount(hpage));

13
mm/migrate.c
View File

@ -1324,8 +1324,19 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
goto put_anon;
if (page_mapped(hpage)) {
struct address_space *mapping = page_mapping(hpage);
/*
* try_to_unmap could potentially call huge_pmd_unshare.
* Because of this, take semaphore in write mode here and
* set TTU_RMAP_LOCKED to let lower levels know we have
* taken the lock.
*/
i_mmap_lock_write(mapping);
try_to_unmap(hpage,
TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS|
TTU_RMAP_LOCKED);
i_mmap_unlock_write(mapping);
page_was_mapped = 1;
}

4
mm/rmap.c
View File

@ -25,6 +25,7 @@
* page->flags PG_locked (lock_page)
* hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share)
* mapping->i_mmap_rwsem
* hugetlb_fault_mutex (hugetlbfs specific page fault mutex)
* anon_vma->rwsem
* mm->page_table_lock or pte_lock
* zone_lru_lock (in mark_page_accessed, isolate_lru_page)
@ -1378,6 +1379,9 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
/*
* If sharing is possible, start and end will be adjusted
* accordingly.
*
* If called for a huge page, caller must hold i_mmap_rwsem
* in write mode as it is possible to call huge_pmd_unshare.
*/
adjust_range_if_pmd_sharing_possible(vma, &range.start,
&range.end);

11
mm/userfaultfd.c
View File

@ -267,10 +267,14 @@ retry:
VM_BUG_ON(dst_addr & ~huge_page_mask(h));
/*
* Serialize via hugetlb_fault_mutex
* Serialize via i_mmap_rwsem and hugetlb_fault_mutex.
* i_mmap_rwsem ensures the dst_pte remains valid even
* in the case of shared pmds. fault mutex prevents
* races with other faulting threads.
*/
idx = linear_page_index(dst_vma, dst_addr);
mapping = dst_vma->vm_file->f_mapping;
i_mmap_lock_read(mapping);
idx = linear_page_index(dst_vma, dst_addr);
hash = hugetlb_fault_mutex_hash(h, dst_mm, dst_vma, mapping,
idx, dst_addr);
mutex_lock(&hugetlb_fault_mutex_table[hash]);
@ -279,6 +283,7 @@ retry:
dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h));
if (!dst_pte) {
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
i_mmap_unlock_read(mapping);
goto out_unlock;
}
@ -286,6 +291,7 @@ retry:
dst_pteval = huge_ptep_get(dst_pte);
if (!huge_pte_none(dst_pteval)) {
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
i_mmap_unlock_read(mapping);
goto out_unlock;
}
@ -293,6 +299,7 @@ retry:
dst_addr, src_addr, &page);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
i_mmap_unlock_read(mapping);
vm_alloc_shared = vm_shared;
cond_resched();