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hugetlb: unshare some PMDs when splitting VMAs

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PMD sharing can only be done in PUD_SIZE-aligned pieces of VMAs; however,
it is possible that HugeTLB VMAs are split without unsharing the PMDs
first.

Without this fix, it is possible to hit the uffd-wp-related WARN_ON_ONCE
in hugetlb_change_protection [1].  The key there is that
hugetlb_unshare_all_pmds will not attempt to unshare PMDs in
non-PUD_SIZE-aligned sections of the VMA.

It might seem ideal to unshare in hugetlb_vm_op_open, but we need to
unshare in both the new and old VMAs, so unsharing in hugetlb_vm_op_split
seems natural.

[1]: https://lore.kernel.org/linux-mm/CADrL8HVeOkj0QH5VZZbRzybNE8CG-tEGFshnA+bG9nMgcWtBSg@mail.gmail.com/

Link: https://lkml.kernel.org/r/20230104231910.1464197-1-jthoughton@google.com
Fixes: 6dfeaff93b ("hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp")
Signed-off-by: James Houghton <jthoughton@google.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
James Houghton 2023-01-04 23:19:10 +00:00 committed by Andrew Morton
parent a1193de562
commit b30c14cd61
1 changed files with 35 additions and 9 deletions
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44
mm/hugetlb.c
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@ -94,6 +94,8 @@ static int hugetlb_acct_memory(struct hstate *h, long delta);
static void hugetlb_vma_lock_free(struct vm_area_struct *vma);
static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma);
static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma);
static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
unsigned long start, unsigned long end);
static inline bool subpool_is_free(struct hugepage_subpool *spool)
{
@ -4834,6 +4836,25 @@ static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
{
if (addr & ~(huge_page_mask(hstate_vma(vma))))
return -EINVAL;
/*
* PMD sharing is only possible for PUD_SIZE-aligned address ranges
* in HugeTLB VMAs. If we will lose PUD_SIZE alignment due to this
* split, unshare PMDs in the PUD_SIZE interval surrounding addr now.
*/
if (addr & ~PUD_MASK) {
/*
* hugetlb_vm_op_split is called right before we attempt to
* split the VMA. We will need to unshare PMDs in the old and
* new VMAs, so let's unshare before we split.
*/
unsigned long floor = addr & PUD_MASK;
unsigned long ceil = floor + PUD_SIZE;
if (floor >= vma->vm_start && ceil <= vma->vm_end)
hugetlb_unshare_pmds(vma, floor, ceil);
}
return 0;
}
@ -7322,26 +7343,21 @@ void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio, int re
}
}
/*
* This function will unconditionally remove all the shared pmd pgtable entries
* within the specific vma for a hugetlbfs memory range.
*/
void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
unsigned long start,
unsigned long end)
{
struct hstate *h = hstate_vma(vma);
unsigned long sz = huge_page_size(h);
struct mm_struct *mm = vma->vm_mm;
struct mmu_notifier_range range;
unsigned long address, start, end;
unsigned long address;
spinlock_t *ptl;
pte_t *ptep;
if (!(vma->vm_flags & VM_MAYSHARE))
return;
start = ALIGN(vma->vm_start, PUD_SIZE);
end = ALIGN_DOWN(vma->vm_end, PUD_SIZE);
if (start >= end)
return;
@ -7373,6 +7389,16 @@ void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
mmu_notifier_invalidate_range_end(&range);
}
/*
* This function will unconditionally remove all the shared pmd pgtable entries
* within the specific vma for a hugetlbfs memory range.
*/
void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
{
hugetlb_unshare_pmds(vma, ALIGN(vma->vm_start, PUD_SIZE),
ALIGN_DOWN(vma->vm_end, PUD_SIZE));
}
#ifdef CONFIG_CMA
static bool cma_reserve_called __initdata;