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    Subject[PATCHv2 12/41] thp: handle write-protection faults for file THP
    Date
    For filesystems that wants to be write-notified (has mkwrite), we will
    encount write-protection faults for huge PMDs in shared mappings.

    The easiest way to handle them is to clear the PMD and let it refault as
    wriable.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    mm/memory.c | 11 ++++++++++-
    1 file changed, 10 insertions(+), 1 deletion(-)

    diff --git a/mm/memory.c b/mm/memory.c
    index 4425b6059339..5b7f0ce44a27 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -3448,8 +3448,17 @@ static int wp_huge_pmd(struct fault_env *fe, pmd_t orig_pmd)
    return fe->vma->vm_ops->pmd_fault(fe->vma, fe->address, fe->pmd,
    fe->flags);

    + if (fe->vma->vm_flags & VM_SHARED) {
    + /* Clear PMD */
    + zap_page_range_single(fe->vma, fe->address,
    + HPAGE_PMD_SIZE, NULL);
    + VM_BUG_ON(!pmd_none(*fe->pmd));
    +
    + /* Refault to establish writable PMD */
    + return 0;
    + }
    +
    /* COW handled on pte level: split pmd */
    - VM_BUG_ON_VMA(fe->vma->vm_flags & VM_SHARED, fe->vma);
    split_huge_pmd(fe->vma, fe->pmd, fe->address);

    return VM_FAULT_FALLBACK;
    --
    2.8.1
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