tools/testing/selftests: explicitly test split multi VMA mremap move

Check that moving a range of VMAs where we are offset into the first and
last VMAs works correctly.

This results in the VMAs being split at these points at which we are offset
into VMAs.

We explicitly test both the ordinary MREMAP_FIXED multi VMA move case and
the MREMAP_DONTUNMAP multi VMA move case.

Link: https://lkml.kernel.org/r/b04920bb6c09dc86c207c251eab8ec670fbbcaef.1753119043.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: lorenzo-stoakes

tools/testing/selftests/mm/mremap_test.c

@@ -610,6 +610,129 @@ static void mremap_shrink_multiple_vmas(unsigned long page_size,
 				      inplace ? " [inplace]" : "");
 }
 
+static void mremap_move_multiple_vmas_split(unsigned int pattern_seed,
+					    unsigned long page_size,
+					    bool dont_unmap)
+{
+	char *test_name = "mremap move multiple vmas split";
+	int mremap_flags = MREMAP_FIXED | MREMAP_MAYMOVE;
+	const size_t size = 10 * page_size;
+	bool success = true;
+	char *ptr, *tgt_ptr;
+	int i;
+
+	if (dont_unmap)
+		mremap_flags |= MREMAP_DONTUNMAP;
+
+	ptr = mmap(NULL, size, PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (ptr == MAP_FAILED) {
+		perror("mmap");
+		success = false;
+		goto out;
+	}
+
+	tgt_ptr = mmap(NULL, size, PROT_READ | PROT_WRITE,
+		       MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (tgt_ptr == MAP_FAILED) {
+		perror("mmap");
+		success = false;
+		goto out;
+	}
+	if (munmap(tgt_ptr, size)) {
+		perror("munmap");
+		success = false;
+		goto out_unmap;
+	}
+
+	/*
+	 * Unmap so we end up with:
+	 *
+	 *  0 1 2 3 4 5 6 7 8 9 10 offset in buffer
+	 * |**********| |*******|
+	 * |**********| |*******|
+	 *  0 1 2 3 4   5 6 7 8 9  pattern offset
+	 */
+	if (munmap(&ptr[5 * page_size], page_size)) {
+		perror("munmap");
+		success = false;
+		goto out_unmap;
+	}
+
+	/* Set up random patterns. */
+	srand(pattern_seed);
+	for (i = 0; i < 10; i++) {
+		int j;
+		char *buf = &ptr[i * page_size];
+
+		if (i == 5)
+			continue;
+
+		for (j = 0; j < page_size; j++)
+			buf[j] = rand();
+	}
+
+	/*
+	 * Move the below:
+	 *
+	 *      <------------->
+	 *  0 1 2 3 4 5 6 7 8 9 10 offset in buffer
+	 * |**********| |*******|
+	 * |**********| |*******|
+	 *  0 1 2 3 4   5 6 7 8 9  pattern offset
+	 *
+	 * Into:
+	 *
+	 * 0 1 2 3 4 5 6 7 offset in buffer
+	 * |*****| |*****|
+	 * |*****| |*****|
+	 * 2 3 4   5 6 7   pattern offset
+	 */
+	if (mremap(&ptr[2 * page_size], size - 3 * page_size, size - 3 * page_size,
+		   mremap_flags, tgt_ptr) == MAP_FAILED) {
+		perror("mremap");
+		success = false;
+		goto out_unmap;
+	}
+
+	/* Offset into random pattern. */
+	srand(pattern_seed);
+	for (i = 0; i < 2 * page_size; i++)
+		rand();
+
+	/* Check pattern. */
+	for (i = 0; i < 7; i++) {
+		int j;
+		char *buf = &tgt_ptr[i * page_size];
+
+		if (i == 3)
+			continue;
+
+		for (j = 0; j < page_size; j++) {
+			char chr = rand();
+
+			if (chr != buf[j]) {
+				ksft_print_msg("page %d offset %d corrupted, expected %d got %d\n",
+					       i, j, chr, buf[j]);
+				goto out_unmap;
+			}
+		}
+	}
+
+out_unmap:
+	if (munmap(tgt_ptr, size))
+		perror("munmap tgt");
+	if (munmap(ptr, size))
+		perror("munmap src");
+out:
+	if (success)
+		ksft_test_result_pass("%s%s\n", test_name,
+				      dont_unmap ? " [dontunnmap]" : "");
+	else
+		ksft_test_result_fail("%s%s\n", test_name,
+				      dont_unmap ? " [dontunnmap]" : "");
+}
+
 /* Returns the time taken for the remap on success else returns -1. */
 static long long remap_region(struct config c, unsigned int threshold_mb,
 			      char *rand_addr)
@@ -951,7 +1074,7 @@ int main(int argc, char **argv)
 	char *rand_addr;
 	size_t rand_size;
 	int num_expand_tests = 2;
-	int num_misc_tests = 6;
+	int num_misc_tests = 8;
 	struct test test_cases[MAX_TEST] = {};
 	struct test perf_test_cases[MAX_PERF_TEST];
 	int page_size;
@@ -1082,6 +1205,8 @@ int main(int argc, char **argv)
 	mremap_shrink_multiple_vmas(page_size, /* inplace= */false);
 	mremap_move_multiple_vmas(pattern_seed, page_size, /* dontunmap= */ false);
 	mremap_move_multiple_vmas(pattern_seed, page_size, /* dontunmap= */ true);
+	mremap_move_multiple_vmas_split(pattern_seed, page_size, /* dontunmap= */ false);
+	mremap_move_multiple_vmas_split(pattern_seed, page_size, /* dontunmap= */ true);
 
 	if (run_perf_tests) {
 		ksft_print_msg("\n%s\n",