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hugetlbfs: flush TLBs correctly after huge_pmd_unshare

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When __unmap_hugepage_range() calls to huge_pmd_unshare() succeed, a TLB
flush is missing.  This TLB flush must be performed before releasing the
i_mmap_rwsem, in order to prevent an unshared PMDs page from being
released and reused before the TLB flush took place.

Arguably, a comprehensive solution would use mmu_gather interface to
batch the TLB flushes and the PMDs page release, however it is not an
easy solution: (1) try_to_unmap_one() and try_to_migrate_one() also call
huge_pmd_unshare() and they cannot use the mmu_gather interface; and (2)
deferring the release of the page reference for the PMDs page until
after i_mmap_rwsem is dropeed can confuse huge_pmd_unshare() into
thinking PMDs are shared when they are not.

Fix __unmap_hugepage_range() by adding the missing TLB flush, and
forcing a flush when unshare is successful.

Fixes: 24669e5847 ("hugetlb: use mmu_gather instead of a temporary linked list for accumulating pages)" # 3.6
Signed-off-by: Nadav Amit <namit@vmware.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nadav Amit 2021-11-21 12:40:07 -08:00 committed by Linus Torvalds
parent 1360572566
commit a4a118f2ee
1 changed files with 19 additions and 4 deletions
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23
mm/hugetlb.c
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@ -4939,6 +4939,7 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
struct hstate *h = hstate_vma(vma);
unsigned long sz = huge_page_size(h);
struct mmu_notifier_range range;
bool force_flush = false;
WARN_ON(!is_vm_hugetlb_page(vma));
BUG_ON(start & ~huge_page_mask(h));
@ -4967,10 +4968,8 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
ptl = huge_pte_lock(h, mm, ptep);
if (huge_pmd_unshare(mm, vma, &address, ptep)) {
spin_unlock(ptl);
/*
* We just unmapped a page of PMDs by clearing a PUD.
* The caller's TLB flush range should cover this area.
*/
tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE);
force_flush = true;
continue;
}
@ -5027,6 +5026,22 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
}
mmu_notifier_invalidate_range_end(&range);
tlb_end_vma(tlb, vma);
/*
* If we unshared PMDs, the TLB flush was not recorded in mmu_gather. We
* could defer the flush until now, since by holding i_mmap_rwsem we
* guaranteed that the last refernece would not be dropped. But we must
* do the flushing before we return, as otherwise i_mmap_rwsem will be
* dropped and the last reference to the shared PMDs page might be
* dropped as well.
*
* In theory we could defer the freeing of the PMD pages as well, but
* huge_pmd_unshare() relies on the exact page_count for the PMD page to
* detect sharing, so we cannot defer the release of the page either.
* Instead, do flush now.
*/
if (force_flush)
tlb_flush_mmu_tlbonly(tlb);
}
void __unmap_hugepage_range_final(struct mmu_gather *tlb,