[PATCHv3 12/41] thp: handle write-protection faults for file THP

Kirill A. Shutemov
2016-09-15T11:54:54Z

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 83be99d9d8a1..aad8d5c6311f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3451,8 +3451,17 @@ 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;