[PATCH v3 1/1] selftests/mm: skip soft-dirty tests when CONFIG_MEM_SOFT_DIRTY is disabled

Lance Yang
2025-09-17T13:33:56Z

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.

Acked-by: David Hildenbrand <david@redhat.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Lance Yang <lance.yang@linux.dev>
---
v2 -> v3:
- Optimize softdirty_supported() by directly assigning check_vmflag()
result (per David)
- Pick AB from David - thanks!
- https://lore.kernel.org/lkml/20250917122750.36608-1-lance.yang@linux.dev

v1 -> v2:
- Rename softdirty_is_supported() to softdirty_supported() (per David)
- Drop aarch64 specific handling (per David)
- https://lore.kernel.org/lkml/20250917055913.49759-1-lance.yang@linux.dev

tools/testing/selftests/mm/madv_populate.c | 21 ++-------------------
tools/testing/selftests/mm/soft-dirty.c | 5 ++++-
tools/testing/selftests/mm/vm_util.c | 17 +++++++++++++++++
tools/testing/selftests/mm/vm_util.h | 1 +
4 files changed, 24 insertions(+), 20 deletions(-)

diff --git a/tools/testing/selftests/mm/madv_populate.c b/tools/testing/selftests/mm/madv_populate.c
index b6fabd5c27ed..d8d11bc67ddc 100644
--- a/tools/testing/selftests/mm/madv_populate.c
+++ b/tools/testing/selftests/mm/madv_populate.c
@@ -264,23 +264,6 @@ static void test_softdirty(void)
munmap(addr, SIZE);
}

-static int system_has_softdirty(void)
-{
- /*
- * There is no way to check if the kernel supports soft-dirty, other
- * than by writing to a page and seeing if the bit was set. But the
- * tests are intended to check that the bit gets set when it should, so
- * doing that check would turn a potentially legitimate fail into a
- * skip. Fortunately, we know for sure that arm64 does not support
- * soft-dirty. So for now, let's just use the arch as a corse guide.
- */
-#if defined(__aarch64__)
- return 0;
-#else
- return 1;
-#endif
-}
-
int main(int argc, char **argv)
{
int nr_tests = 16;
@@ -288,7 +271,7 @@ int main(int argc, char **argv)

pagesize = getpagesize();

- if (system_has_softdirty())
+ if (softdirty_supported())
nr_tests += 5;

ksft_print_header();
@@ -300,7 +283,7 @@ int main(int argc, char **argv)
test_holes();
test_populate_read();
test_populate_write();
- if (system_has_softdirty())
+ if (softdirty_supported())
test_softdirty();

err = ksft_get_fail_cnt();
diff --git a/tools/testing/selftests/mm/soft-dirty.c b/tools/testing/selftests/mm/soft-dirty.c
index 8a3f2b4b2186..4ee4db3750c1 100644
--- a/tools/testing/selftests/mm/soft-dirty.c
+++ b/tools/testing/selftests/mm/soft-dirty.c
@@ -200,8 +200,11 @@ 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/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 56e9bd541edd..e33cda301dad 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -449,6 +449,23 @@ bool check_vmflag_pfnmap(void *addr)
return check_vmflag(addr, "pf");
}

+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;
+}
+
/*
* Open an fd at /proc/$pid/maps and configure procmap_out ready for
* PROCMAP_QUERY query. Returns 0 on success, or an error code otherwise.
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 07c4acfd84b6..26c30fdc0241 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -104,6 +104,7 @@ bool find_vma_procmap(struct procmap_fd *procmap, void *address);
int close_procmap(struct procmap_fd *procmap);
int write_sysfs(const char *file_path, unsigned long val);
int read_sysfs(const char *file_path, unsigned long *val);
+bool softdirty_supported(void);

static inline int open_self_procmap(struct procmap_fd *procmap_out)
{
--
2.49.0