On 9/2/26 20:00, Lorenzo Stoakes (ARM) wrote:
> Assert that MAP_PRIVATE-mapped /dev/zero mappings behave like they are
> anonymous.
>
> We test both unfaulted and faulted/unfaulted merges - each with the regions
> having page offset of 0, which would not merge if the mappings were treated
> as if they were file-backed.
>
> With the recent change that makes them behave as pure anonymous mappings,
> the merges should succeed as their page offsets are equal to their
> anonymous page offsets.
>
> Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
> ---
> tools/testing/selftests/mm/merge.c | 104
> +++++++++++++++++++++++++++++++++++++
> 1 file changed, 104 insertions(+)
>
> diff --git a/tools/testing/selftests/mm/merge.c
> b/tools/testing/selftests/mm/merge.c
> index 52b8727b6628..7c528d470404 100644
> --- a/tools/testing/selftests/mm/merge.c
> +++ b/tools/testing/selftests/mm/merge.c
> @@ -1362,6 +1362,110 @@ TEST_F(merge, anon_and_page_offset_mismatch_memfd)
> ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 5 * page_size);
> }
>
> +TEST_F(merge, merge_map_private_dev_zero_unfaulted)
> +{
> + struct procmap_fd *procmap = &self->procmap;
> + unsigned int page_size = self->page_size;
> + char *carveout = self->carveout;
> + char *ptr, *ptr2;
> + int fd_zero;
> +
> + if (access("/dev/zero", F_OK))
> + SKIP(return, "No /dev/zero.");
> + fd_zero = open("/dev/zero", O_RDWR);
> + ASSERT_NE(fd_zero, -1);
> +
> + /*
> + * Map two MAP_PRIVATE-/dev/zero VMAs next to one another with offset 0
> + * each.
> + *
> + * With these being made truly anonymous upon mapping, they will
> + * merge. If they were file-backed VMAs the page offsets would prevent
> + * merge:
Nit: "the" merge? You're the native speaker, so I don't know if what you have is
just correct :)
> + *
> + * |-----||------| |-------------|
> + * | ptr || ptr2 | -> | ptr |
> + * |-----||------| |-------------|
> + */
> + ptr = mmap(carveout, 5 * page_size, PROT_READ | PROT_WRITE,
> + MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
> + if (ptr == MAP_FAILED) {
> + close(fd_zero);
> + ASSERT_TRUE(false);
> + }
> + ptr2 = mmap(&carveout[5 * page_size], 5 * page_size,
> + PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
> + if (ptr2 == MAP_FAILED) {
> + close(fd_zero);
Is the close() really required before the ASSERT? After all, you're also not
munmap'ing, so I wonder to which degree we have to clean up.
So maybe this could just become a
ASSERT_NE(ptr2, MAP_FAILED);
Same for ptr above.
You could likely also do
ptr = mmap()
ptr2 = mmap()
close(fd_zero);
ASSERT_NE(ptr, MAP_FAILED);
ASSERT_NE(ptr2, MAP_FAILED);
> + ASSERT_TRUE(false);
> + }
> + close(fd_zero);
> +
> + /* Assert that they merged. */
> + 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 + 10 * page_size);
> +}
> +
> +TEST_F(merge, merge_map_private_dev_zero_faulted_unfaulted)
> +{
> + struct procmap_fd *procmap = &self->procmap;
> + unsigned int page_size = self->page_size;
> + char *carveout = self->carveout;
> + char *ptr, *ptr2;
> + int fd_zero;
> +
> + if (access("/dev/zero", F_OK))
> + SKIP(return, "No /dev/zero.");
> + fd_zero = open("/dev/zero", O_RDWR);
> + ASSERT_NE(fd_zero, -1);
> +
> + /*
> + * Map a MAP_PRIVATE mapping of /dev/zero with page offset 0, then fault
> + * it in:
> + *
> + * |-------------------------------|
> + * | faulted |
> + * |-------------------------------|
> + */
> + ptr = mmap(carveout, 15 * page_size, PROT_READ | PROT_WRITE,
> + MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
> + if (ptr == MAP_FAILED) {
> + close(fd_zero);
> + ASSERT_TRUE(false);
Same question regarding cleanup requirements. The ASSERT_TRUE(false) looks a bit
odd.
--
Cheers,
David
