[PATCH 6.1.y 1/1] selftests/mm: skip soft-dirty tests when CONFIG_MEM_SOFT_DIRTY is disabled

[Lance Yang <lance.yang@linux.dev>]

From: Lance Yang <lance.yang@linux.dev>

The madv_populate and soft-dirty kselftests currently fail on systems
where CONFIG_MEM_SOFT_DIRTY is disabled.

Introduce a new helper softdirty_supported() into vm_util.c/h to ensure
tests are properly skipped when the feature is not enabled.

Link: https://lkml.kernel.org/r/20250917133137.62802-1-lance.yang@linux.dev
Fixes: 9f3265db6ae8 ("selftests: vm: add test for Soft-Dirty PTE bit")
Signed-off-by: Lance Yang <lance.yang@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Gabriel Krisman Bertazi <krisman@collabora.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 0389c305ef56cbadca4cbef44affc0ec3213ed30)
---
 tools/testing/selftests/vm/madv_populate.c |  9 ++-
 tools/testing/selftests/vm/soft-dirty.c    |  5 +-
 tools/testing/selftests/vm/vm_util.c       | 77 ++++++++++++++++++++++
 tools/testing/selftests/vm/vm_util.h       |  2 +
 4 files changed, 90 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/vm/madv_populate.c b/tools/testing/selftests/vm/madv_populate.c
index 715a42e8e2cd..f37bda59c18c 100644
--- a/tools/testing/selftests/vm/madv_populate.c
+++ b/tools/testing/selftests/vm/madv_populate.c
@@ -274,12 +274,16 @@ static void test_softdirty(void)
 
 int main(int argc, char **argv)
 {
+	int nr_tests = 16;
 	int err;
 
 	pagesize = getpagesize();
 
+	if (softdirty_supported())
+		nr_tests += 5;
+
 	ksft_print_header();
-	ksft_set_plan(21);
+	ksft_set_plan(nr_tests);
 
 	sense_support();
 	test_prot_read();
@@ -287,7 +291,8 @@ int main(int argc, char **argv)
 	test_holes();
 	test_populate_read();
 	test_populate_write();
-	test_softdirty();
+	if (softdirty_supported())
+		test_softdirty();
 
 	err = ksft_get_fail_cnt();
 	if (err)
diff --git a/tools/testing/selftests/vm/soft-dirty.c b/tools/testing/selftests/vm/soft-dirty.c
index 21d8830c5f24..615ab2d204ef 100644
--- a/tools/testing/selftests/vm/soft-dirty.c
+++ b/tools/testing/selftests/vm/soft-dirty.c
@@ -190,8 +190,11 @@ int main(int argc, char **argv)
 	int pagesize;
 
 	ksft_print_header();
-	ksft_set_plan(15);
 
+	if (!softdirty_supported())
+		ksft_exit_skip("soft-dirty is not support\n");
+
+	ksft_set_plan(15);
 	pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
 	if (pagemap_fd < 0)
 		ksft_exit_fail_msg("Failed to open %s\n", PAGEMAP_FILE_PATH);
diff --git a/tools/testing/selftests/vm/vm_util.c b/tools/testing/selftests/vm/vm_util.c
index f11f8adda521..fc5743bc1283 100644
--- a/tools/testing/selftests/vm/vm_util.c
+++ b/tools/testing/selftests/vm/vm_util.c
@@ -72,6 +72,42 @@ uint64_t read_pmd_pagesize(void)
 	return strtoul(buf, NULL, 10);
 }
 
+char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
+{
+	int ret;
+	FILE *fp;
+	char *entry = NULL;
+	char addr_pattern[MAX_LINE_LENGTH];
+
+	ret = snprintf(addr_pattern, MAX_LINE_LENGTH, "%08lx-",
+		       (unsigned long)addr);
+	if (ret >= MAX_LINE_LENGTH)
+		ksft_exit_fail_msg("%s: Pattern is too long\n", __func__);
+
+	fp = fopen(SMAP_FILE_PATH, "r");
+	if (!fp)
+		ksft_exit_fail_msg("%s: Failed to open file %s\n", __func__,
+				   SMAP_FILE_PATH);
+
+	if (!check_for_pattern(fp, addr_pattern, buf, len))
+		goto err_out;
+
+	/* Fetch the pattern in the same block */
+	if (!check_for_pattern(fp, pattern, buf, len))
+		goto err_out;
+
+	/* Trim trailing newline */
+	entry = strchr(buf, '\n');
+	if (entry)
+		*entry = '\0';
+
+	entry = buf + strlen(pattern);
+
+err_out:
+	fclose(fp);
+	return entry;
+}
+
 bool __check_huge(void *addr, char *pattern, int nr_hpages,
 		  uint64_t hpage_size)
 {
@@ -124,3 +160,44 @@ bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size)
 {
 	return __check_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
 }
+
+static bool check_vmflag(void *addr, const char *flag)
+{
+	char buffer[MAX_LINE_LENGTH];
+	const char *flags;
+	size_t flaglen;
+
+	flags = __get_smap_entry(addr, "VmFlags:", buffer, sizeof(buffer));
+	if (!flags)
+		ksft_exit_fail_msg("%s: No VmFlags for %p\n", __func__, addr);
+
+	while (true) {
+		flags += strspn(flags, " ");
+
+		flaglen = strcspn(flags, " ");
+		if (!flaglen)
+			return false;
+
+		if (flaglen == strlen(flag) && !memcmp(flags, flag, flaglen))
+			return true;
+
+		flags += flaglen;
+	}
+}
+
+bool softdirty_supported(void)
+{
+	char *addr;
+	bool supported = false;
+	const size_t pagesize = getpagesize();
+
+	/* New mappings are expected to be marked with VM_SOFTDIRTY (sd). */
+	addr = mmap(0, pagesize, PROT_READ | PROT_WRITE,
+		    MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
+	if (!addr)
+		ksft_exit_fail_msg("mmap failed\n");
+
+	supported = check_vmflag(addr, "sd");
+	munmap(addr, pagesize);
+	return supported;
+}
diff --git a/tools/testing/selftests/vm/vm_util.h b/tools/testing/selftests/vm/vm_util.h
index 5c35de454e08..470f85fe9594 100644
--- a/tools/testing/selftests/vm/vm_util.h
+++ b/tools/testing/selftests/vm/vm_util.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #include <stdint.h>
 #include <stdbool.h>
+#include <sys/mman.h>
 
 uint64_t pagemap_get_entry(int fd, char *start);
 bool pagemap_is_softdirty(int fd, char *start);
@@ -10,3 +11,4 @@ uint64_t read_pmd_pagesize(void);
 bool check_huge_anon(void *addr, int nr_hpages, uint64_t hpage_size);
 bool check_huge_file(void *addr, int nr_hpages, uint64_t hpage_size);
 bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size);
+bool softdirty_supported(void);
-- 
2.49.0