Re: [PATCH v3 7/7] selftest/mm: ksm_functional_tests: Add PROT_NONE test

On Thu, Aug 03, 2023 at 04:32:08PM +0200, David Hildenbrand wrote:

Let's test whether merging and unmerging in PROT_NONE areas works as expected.

Pass a page protection to mmap_and_merge_range(), which will trigger an mprotect() after writing to the pages, but before enabling merging.

Make sure that unsharing works as expected, by performing a ptrace write (using /proc/self/mem) and by setting MADV_UNMERGEABLE.

Note that this implicitly tests that ptrace writes in an inaccessible (PROT_NONE) mapping work as expected.

Signed-off-by: David Hildenbrand david@redhat.com

[...]

+static void test_prot_none(void) +{

• const unsigned int size = 2 * MiB;
• char *map;
• int i;
• ksft_print_msg("[RUN] %s\n", __func__);
• map = mmap_and_merge_range(0x11, size, PROT_NONE, false);
• if (map == MAP_FAILED)

• goto unmap;
  

• /* Store a unique value in each page on one half using ptrace */
• for (i = 0; i < size / 2; i += pagesize) {

• lseek(mem_fd, (uintptr_t) map + i, SEEK_SET);
  

• if (write(mem_fd, &i, sizeof(size)) != sizeof(size)) {
  

sizeof(i)? May not matter a huge lot, though..

• 	ksft_test_result_fail("ptrace write failed\n");
  

• 	goto unmap;
  

• }
  

• }

Acked-by: Peter Xu peterx@redhat.com