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

[Lorenzo Stoakes (Oracle)]

On Tue, Mar 31, 2026 at 05:58:51PM -0700, Andrew Morton wrote:
> 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:

Thanks, LGTM!

Cheers, Lorenzo

>
>
> 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;
> _
>