Re: [PATCH v2] tools/testing/selftests: add merge test for partial msealed range

[Andrew Morton]

On Tue, 31 Mar 2026 11:08:03 +0100 "Lorenzo Stoakes (Oracle)" <ljs@xxxxxxxxxx> wrote:

> Then again, and contradicting myself elsewhere on fix-patches blah blah blah,
> since this is just test code, I checked the below and it works the same and
> triggers the regression.
> 
> So maybe we can just apply that?

Here's how the two folded together will look:


From: "Lorenzo Stoakes (Oracle)" <ljs@xxxxxxxxxx>
Subject: tools/testing/selftests: add merge test for partial msealed range
Date: Tue, 31 Mar 2026 08:36:27 +0100

Commit 2697dd8ae721 ("mm/mseal: update VMA end correctly on merge") fixed
an issue in the loop which iterates through VMAs applying mseal, which was
triggered by mseal()'ing a range of VMAs where the second was mseal()'d
and the first mergeable with it, once mseal()'d.

Add a regression test to assert that this behaviour is correct.  We place
it in the merge selftests as this is strictly an issue with merging (via a
vma_modify() invocation).

It also asserts that mseal()'d ranges are correctly merged as you'd
expect.

The test is implemented such that it is skipped if mseal() is not
available on the system.

[ljs@xxxxxxxxxx: simplifications per Pedro]
  Link: https://lkml.kernel.org/r/1c9c922d-5cb5-4cff-9273-b737cdb57ca1@lucifer.local
Link: https://lkml.kernel.org/r/20260331073627.50010-1-ljs@xxxxxxxxxx
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Liam Howlett <liam.howlett@xxxxxxxxxx>
Cc: Lorenzo Stoakes <ljs@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Pedro Falcato <pfalcato@xxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 tools/testing/selftests/mm/merge.c |   89 +++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)

--- a/tools/testing/selftests/mm/merge.c~tools-testing-selftests-add-merge-test-for-partial-msealed-range
+++ a/tools/testing/selftests/mm/merge.c
@@ -2,6 +2,7 @@
 
 #define _GNU_SOURCE
 #include "kselftest_harness.h"
+#include <asm-generic/unistd.h>
 #include <linux/prctl.h>
 #include <fcntl.h>
 #include <stdio.h>
@@ -48,6 +49,19 @@ static pid_t do_fork(struct procmap_fd *
 	return 0;
 }
 
+#ifdef __NR_mseal
+static int sys_mseal(void *ptr, size_t len, unsigned long flags)
+{
+	return syscall(__NR_mseal, (unsigned long)ptr, len, flags);
+}
+#else
+static int sys_mseal(void *ptr, size_t len, unsigned long flags)
+{
+	errno = ENOSYS;
+	return -1;
+}
+#endif
+
 FIXTURE_SETUP(merge)
 {
 	self->page_size = psize();
@@ -1217,6 +1231,81 @@ TEST_F(merge, mremap_correct_placed_faul
 	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 15 * page_size);
 }
 
+TEST_F(merge, merge_vmas_with_mseal)
+{
+	unsigned int page_size = self->page_size;
+	struct procmap_fd *procmap = &self->procmap;
+	char *ptr, *ptr2, *ptr3;
+	/* We need our own as cannot munmap() once sealed. */
+	char *carveout;
+
+	/* Invalid mseal() call to see if implemented. */
+	ASSERT_EQ(sys_mseal(NULL, 0, ~0UL), -1);
+	if (errno == ENOSYS)
+		SKIP(return, "mseal not supported, skipping.");
+
+	/* Map carveout. */
+	carveout = mmap(NULL, 5 * page_size, PROT_NONE,
+			MAP_PRIVATE | MAP_ANON, -1, 0);
+	ASSERT_NE(carveout, MAP_FAILED);
+
+	/*
+	 * Map 3 separate VMAs:
+	 *
+	 * |-----------|-----------|-----------|
+	 * |    RW     |    RWE    |    RO     |
+	 * |-----------|-----------|-----------|
+	 *      ptr         ptr2        ptr3
+	 */
+	ptr = mmap(&carveout[page_size], page_size, PROT_READ | PROT_WRITE,
+		   MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+	ptr2 = mmap(&carveout[2 * page_size], page_size,
+		    PROT_READ | PROT_WRITE | PROT_EXEC,
+		   MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+	ASSERT_NE(ptr2, MAP_FAILED);
+	ptr3 = mmap(&carveout[3 * page_size], page_size, PROT_READ,
+		   MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+	ASSERT_NE(ptr3, MAP_FAILED);
+
+	/*
+	 * mseal the second VMA:
+	 *
+	 * |-----------|-----------|-----------|
+	 * |    RW     |    RWES   |    RO     |
+	 * |-----------|-----------|-----------|
+	 *      ptr         ptr2        ptr3
+	 */
+	ASSERT_EQ(sys_mseal(ptr2, page_size, 0), 0);
+
+	/* Make first VMA mergeable upon mseal. */
+	ASSERT_EQ(mprotect(ptr, page_size,
+			   PROT_READ | PROT_WRITE | PROT_EXEC), 0);
+	/*
+	 * At this point we have:
+	 *
+	 * |-----------|-----------|-----------|
+	 * |    RWE    |    RWES   |    RO     |
+	 * |-----------|-----------|-----------|
+	 *      ptr         ptr2        ptr3
+	 *
+	 * Now mseal all of the VMAs.
+	 */
+	ASSERT_EQ(sys_mseal(ptr, 3 * page_size, 0), 0);
+
+	/*
+	 * We should end up with:
+	 *
+	 * |-----------------------|-----------|
+	 * |          RWES         |    ROS    |
+	 * |-----------------------|-----------|
+	 *            ptr               ptr3
+	 */
+	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
+	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
+	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 2 * page_size);
+}
+
 TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_prev)
 {
 	struct procmap_fd *procmap = &self->procmap;
_