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mm/userfaultfd: compare exact registration modes before skipping

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Changing registration from MISSING|WP to WP returns success but leaves
MISSING enabled. The no-op check sees that WP is already set and skips
the update, so later accesses to missing pages still wait for userspace.

Skip the update only when the current and requested UFFD modes match
exactly.

Fixes: 63b2d4174c ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl")
Cc: stable@vger.kernel.org
Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
[ david: apply fixup from Lorenzo ]
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Link: https://patch.msgid.link/20261031-fixes_core-v3-26-d6437171ecc3@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
This commit is contained in:
Gregory Price 2026-10-31 10:39:55 +01:00 committed by David Hildenbrand (Arm)
parent 4eee9c389b
commit 05f64f211a
1 changed files with 2 additions and 1 deletions
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3
mm/userfaultfd.c
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@ -2291,6 +2291,7 @@ static int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
for_each_vma_range(vmi, vma, end) {
const bool any_mode_removed = vma->vm_flags & __VM_UFFD_FLAGS & ~vm_flags;
const vma_flags_t curr_vma_flags = vma_flags_and_mask(&vma->flags, __VMA_UFFD_FLAGS);
cond_resched();
@ -2304,7 +2305,7 @@ static int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
* userfaultfd and with the right tracking mode too.
*/
if (vma->vm_userfaultfd_ctx.ctx == ctx &&
vma_test_all_mask(vma, vma_flags))
vma_flags_same_pair(&curr_vma_flags, &vma_flags))
goto skip;
/*