+ kselftest-mm-fix-potential-failure-for-merged-vma-in-guard-regions.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: kselftest: mm: fix potential failure for merged VMA in guard-regions
has been added to the -mm mm-new branch.  Its filename is
     kselftest-mm-fix-potential-failure-for-merged-vma-in-guard-regions.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kselftest-mm-fix-potential-failure-for-merged-vma-in-guard-regions.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Yeoreum Yun <yeoreum.yun@arm.com>
Subject: kselftest: mm: fix potential failure for merged VMA in guard-regions
Date: Fri, 11 Sep 2026 15:29:03 +0100

check_vmflag_guard() uses /proc/self/smaps to retrieve the VMA flags, but
this can fail if the mapping is merged with an adjacent VMA.

To avoid this potential failure, first allocate a temporary region with
extra pages at both ends, unmap it, and then map the test region within
the temporary address range, leaving an unmapped page on each side to
prevent VMA merging.

Link: https://lore.kernel.org/20260911142904.1825452-1-yeoreum.yun@arm.com
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/guard-regions.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/mm/guard-regions.c~kselftest-mm-fix-potential-failure-for-merged-vma-in-guard-regions
+++ a/tools/testing/selftests/mm/guard-regions.c
@@ -2257,8 +2257,18 @@ TEST_F(guard_regions, smaps)
 	char *ptr, *ptr2;
 	int i;
 
-	/* Map a region. */
-	ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PROT_WRITE, 0, 0);
+	/* Map then unmap placeholder to avoid adjacent merges */
+	ptr = mmap_(self, variant, NULL, 12 * page_size, PROT_NONE, 0, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+	ASSERT_EQ(munmap(ptr, 12 * page_size), 0);
+
+	/*
+	 * Map a region for the test. Since the preceding temporary mapping
+	 * succeeded, this mapping should also succeed without merging with
+	 * adjacent VMAs.
+	 */
+	ptr = mmap_(self, variant, ptr + page_size, 10 * page_size,
+		    PROT_READ | PROT_WRITE, MAP_FIXED, 0);
 	ASSERT_NE(ptr, MAP_FAILED);
 
 	/* We shouldn't yet see a guard flag. */
_

Patches currently in -mm which might be from yeoreum.yun@arm.com are

kselftest-mm-fix-potential-failure-for-merged-vma-in-guard-regions.patch