FAILED: patch "[PATCH] mm/userfaultfd: compare exact registration modes before skipping" failed to apply to 6.6-stable tree

FAILED: patch "[PATCH] mm/userfaultfd: compare exact registration modes before skipping" failed to apply to 6.6-stable tree

[Sasha Levin]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 05f64f211a25f7d9771d4fde109aad97174a1cf3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261109201334-failed-6.6-05f64f211a25@kernel.org' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 05f64f211a25f7d9771d4fde109aad97174a1cf3 Mon Sep 17 00:00:00 2001
From: Gregory Price <gourry@gourry.net>
Date: Sat, 31 Oct 2026 10:39:55 +0100
Subject: [PATCH] mm/userfaultfd: compare exact registration modes before
 skipping

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: 63b2d4174c4a ("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>
---
 mm/userfaultfd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 03f1b15bfe63e..dac696bda19f0 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -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;
 
 		/*
-- 
2.53.0