Re: [PATCH v5 6/7] selftests: mm: Add a test for remapping within a range

On Tue, Aug 22, 2023 at 01:54:59AM +0000, Joel Fernandes (Google) wrote:

Move a block of memory within a memory range. Any alignment optimization on the source address may cause corruption. Verify using kselftest that it works. I have also verified with tracing that such optimization does not happen due to this check in can_align_down():

if (!for_stack && vma->vm_start <= addr_masked) return false;

Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org

tools/testing/selftests/mm/mremap_test.c | 79 +++++++++++++++++++++++- 1 file changed, 78 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/mremap_test.c b/tools/testing/selftests/mm/mremap_test.c index d7366074e2a8..f45d1abedc9c 100644 --- a/tools/testing/selftests/mm/mremap_test.c +++ b/tools/testing/selftests/mm/mremap_test.c @@ -23,6 +23,7 @@ #define VALIDATION_NO_THRESHOLD 0 /* Verify the entire region */

#define MIN(X, Y) ((X) < (Y) ? (X) : (Y)) +#define SIZE_MB(m) ((size_t)m * (1024 * 1024))

Nit in this instance since you always just use an integer, but generally for good practice's sake - shouldn't we place m in parens e.g. (size_t)(m) to avoid broken macro expansion?

struct config { unsigned long long src_alignment; @@ -226,6 +227,79 @@ static void mremap_expand_merge_offset(FILE *maps_fp, unsigned long page_size) ksft_test_result_fail("%s\n", test_name); }

+/*

• • Verify that an mremap within a range does not cause corruption
• • of unrelated part of range.
• • Consider the following range which is 2MB aligned and is
• • a part of a larger 10MB range which is not shown. Each
• • character is 256KB below making the source and destination
• • 2MB each. The lower case letters are moved (s to d) and the
• • upper case letters are not moved. The below test verifies
• • that the upper case S letters are not corrupted by the
• • adjacent mremap.
• • |DDDDddddSSSSssss|
• */

+static void mremap_move_within_range(char pattern_seed) +{

• char *test_name = "mremap mremap move within range";
• void *src, *dest;
• int i, success = 1;
• size_t size = SIZE_MB(20);
• void *ptr = mmap(NULL, size, PROT_READ | PROT_WRITE,

• 	 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  

• if (ptr == MAP_FAILED) {

• perror("mmap");
  

• success = 0;
  

• goto out;
  

• }
• memset(ptr, 0, size);
• src = ptr + SIZE_MB(6);
• src = (void *)((unsigned long)src & ~(SIZE_MB(2) - 1));

It's nitty I know for a test (sorry!) but it'd be nice to place a bitwise alignment trick like this into a helper function or macro if it isn't otherwise avialable.

• /* Set byte pattern for source block. */
• srand(pattern_seed);
• for (i = 0; i < SIZE_MB(2); i++) {

• ((char *)src)[i] = (char) rand();
  

• }
• dest = src - SIZE_MB(2);
• void *new_ptr = mremap(src + SIZE_MB(1), SIZE_MB(1), SIZE_MB(1),

• 				   MREMAP_MAYMOVE | MREMAP_FIXED, dest + SIZE_MB(1));
  

• if (new_ptr == MAP_FAILED) {

• perror("mremap");
  

• success = 0;
  

• goto out;
  

• }
• /* Verify byte pattern after remapping */
• srand(pattern_seed);
• for (i = 0; i < SIZE_MB(1); i++) {

• char c = (char) rand();
  

• if (((char *)src)[i] != c) {
  

• 	ksft_print_msg("Data at src at %d got corrupted due to unrelated mremap\n",
  

• 		       i);
  

• 	ksft_print_msg("Expected: %#x\t Got: %#x\n", c & 0xff,
  

• 			((char *) src)[i] & 0xff);
  

• 	success = 0;
  

• }
  

• }

+out:

• if (munmap(ptr, size) == -1)

• perror("munmap");
  

• if (success)

• ksft_test_result_pass("%s\n", test_name);
  

• else

• ksft_test_result_fail("%s\n", test_name);
  

+}

/*

• Returns the start address of the mapping on success, else returns
• NULL on failure.

@@ -491,6 +565,7 @@ int main(int argc, char **argv) unsigned int threshold_mb = VALIDATION_DEFAULT_THRESHOLD; unsigned int pattern_seed; int num_expand_tests = 2;

• int num_misc_tests = 1; struct test test_cases[MAX_TEST] = {}; struct test perf_test_cases[MAX_PERF_TEST]; int page_size;

@@ -572,7 +647,7 @@ int main(int argc, char **argv) (threshold_mb * _1MB >= _1GB);

ksft_set_plan(ARRAY_SIZE(test_cases) + (run_perf_tests ?

•       ARRAY_SIZE(perf_test_cases) : 0) + num_expand_tests);
  

•       ARRAY_SIZE(perf_test_cases) : 0) + num_expand_tests + num_misc_tests);
  
  

  for (i = 0; i < ARRAY_SIZE(test_cases); i++) run_mremap_test_case(test_cases[i], &failures, threshold_mb,

@@ -590,6 +665,8 @@ int main(int argc, char **argv)

fclose(maps_fp);

• mremap_move_within_range(pattern_seed);
• if (run_perf_tests) { ksft_print_msg("\n%s\n", "mremap HAVE_MOVE_PMD/PUD optimization time comparison for 1GB region:");

-- 2.42.0.rc1.204.g551eb34607-goog

I drew a little diagram for myself and was thereby convinced this was a good test, therefore,

Reviewed-by: Lorenzo Stoakes lstoakes@gmail.com