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Commit 201340ca authored by Nadav Amit's avatar Nadav Amit Committed by Greg Kroah-Hartman
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hugetlbfs: flush TLBs correctly after huge_pmd_unshare 



commit a4a118f2eead1d6c49e00765de89878288d4b890 upstream.

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: 24669e58 ("hugetlb: use mmu_gather instead of a temporary linked list for accumulating pages)" # 3.6
Signed-off-by: default avatarNadav Amit <namit@vmware.com>
Reviewed-by: default avatarMike 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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent e7891b22

mm/hugetlb.c

+19 −4
Original line number Diff line number Diff line
@@ -3589,6 +3589,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, 
	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));
@@ -3617,10 +3618,8 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, 
		ptl = huge_pte_lock(h, mm, ptep);

		if (huge_pmd_unshare(mm, &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;

		}
@@ -3677,6 +3676,22 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, 
	}

	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,