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: 24669e58477e ("hugetlb: use mmu_gather instead of a temporary linked list for accumulating pages)" # 3.6
Signed-off-by: Nadav Amit <>
Reviewed-by: Mike Kravetz <>
Cc: Aneesh Kumar K.V <>
Cc: KAMEZAWA Hiroyuki <>
Cc: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

RELEASE_NOTE=Fixed CVE-2021-4002 in linux-kernel

Change-Id: Ib544906434b7e3f58d6871cafb8b821fa8b7dd6c
Tested-by: Cusky Presubmit Bot <>
Reviewed-by: Vaibhav Rustagi <>
1 file changed