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 <[email protected]> Reviewed-by: Jan Kara <[email protected]> --- mm/memory.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index e18c57bdc75c..e8c04d1d87b8 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3452,8 +3452,17 @@ 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_MASK, + 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; -- 2.9.3
