[040/166] userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork

Commit Message

Andrew Morton April 7, 2020, 3:05 a.m. UTC

From: Peter Xu <[e-mail]>
Subject: userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork

UFFD_EVENT_FORK support for uffd-wp should be already there, except that
we should clean the uffd-wp bit if uffd fork event is not enabled.  Detect
that to avoid _PAGE_UFFD_WP being set even if the VMA is not being tracked
by VM_UFFD_WP.  Do this for both small PTEs and huge PMDs.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Peter Xu <[e-mail]>
Reviewed-by: Jerome Glisse <[e-mail]>
Reviewed-by: Mike Rapoport <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Bobby Powers <[e-mail]>
Cc: Brian Geffon <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Denis Plotnikov <[e-mail]>
Cc: "Dr . David Alan Gilbert" <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: "Kirill A . Shutemov" <[e-mail]>
Cc: Martin Cracauer <[e-mail]>
Cc: Marty McFadden <[e-mail]>
Cc: Maya Gokhale <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Cc: Pavel Emelyanov <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Shaohua Li <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/huge_memory.c |    8 ++++++++
 mm/memory.c      |    8 ++++++++
 2 files changed, 16 insertions(+)

Patch

--- a/mm/huge_memory.c~userfaultfd-wp-drop-_page_uffd_wp-properly-when-fork
+++ a/mm/huge_memory.c
@@ -1044,6 +1044,14 @@  int copy_huge_pmd(struct mm_struct *dst_
 	ret = -EAGAIN;
 	pmd = *src_pmd;
 
+	/*
+	 * Make sure the _PAGE_UFFD_WP bit is cleared if the new VMA
+	 * does not have the VM_UFFD_WP, which means that the uffd
+	 * fork event is not enabled.
+	 */
+	if (!(vma->vm_flags & VM_UFFD_WP))
+		pmd = pmd_clear_uffd_wp(pmd);
+
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 	if (unlikely(is_swap_pmd(pmd))) {
 		swp_entry_t entry = pmd_to_swp_entry(pmd);
--- a/mm/memory.c~userfaultfd-wp-drop-_page_uffd_wp-properly-when-fork
+++ a/mm/memory.c
@@ -785,6 +785,14 @@  copy_one_pte(struct mm_struct *dst_mm, s
 		pte = pte_mkclean(pte);
 	pte = pte_mkold(pte);
 
+	/*
+	 * Make sure the _PAGE_UFFD_WP bit is cleared if the new VMA
+	 * does not have the VM_UFFD_WP, which means that the uffd
+	 * fork event is not enabled.
+	 */
+	if (!(vm_flags & VM_UFFD_WP))
+		pte = pte_clear_uffd_wp(pte);
+
 	page = vm_normal_page(vma, addr, pte);
 	if (page) {
 		get_page(page);