[RFC 5/8] userfaultfd: undo write proctection in unregister

[Shaohua Li <shli@fb.com>]

After a userfaultfd unregister, make sure the range doesn't disable
write in ptes.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Shaohua Li <shli@fb.com>
---
 fs/userfaultfd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 12176b5..c79a3fd 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -953,6 +953,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 		if (vma->vm_start > start)
 			start = vma->vm_start;
 		vma_end = min(end, vma->vm_end);
+		if (userfaultfd_wp(vma))
+			change_protection(vma, start, vma_end,
+				vm_get_page_prot(vma->vm_flags), 1, 0);
 
 		new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
 		prev = vma_merge(mm, prev, start, vma_end, new_flags,
-- 
2.4.6

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