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@xxxxxxxxxxxxxxx>
---
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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