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

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

[Lance Yang]

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_is_supported() into vm_util.c/h to ensure
tests are properly skipped when the feature is not enabled.

Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Lance Yang <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       | 28 ++++++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h       |  1 +
 4 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/tools/testing/selftests/mm/madv_populate.c b/tools/testing/selftests/mm/madv_populate.c
index b6fabd5c27ed..43dac7783004 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_is_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_is_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..98e42d2ac32a 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_is_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..3173335df775 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -449,6 +449,34 @@ bool check_vmflag_pfnmap(void *addr)
 	return check_vmflag(addr, "pf");
 }
 
+bool softdirty_is_supported(void)
+{
+	char *addr;
+	int ret = 0;
+	size_t pagesize;
+
+	/* We know for sure that arm64 does not support soft-dirty. */
+#if defined(__aarch64__)
+	return ret;
+#endif
+	pagesize = getpagesize();
+	/*
+	 * __mmap_complete() always sets VM_SOFTDIRTY for new VMAs, so we
+	 * just mmap a small region and check its VmFlags in /proc/self/smaps
+	 * for the "sd" flag.
+	 */
+	addr = mmap(0, pagesize, PROT_READ | PROT_WRITE,
+		    MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
+	if (!addr)
+		ksft_exit_fail_msg("mmap failed\n");
+
+	if (check_vmflag(addr, "sd"))
+		ret = 1;
+
+	munmap(addr, pagesize);
+	return ret;
+}
+
 /*
  * 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..87ad8e0d92c0 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_is_supported(void);
 
 static inline int open_self_procmap(struct procmap_fd *procmap_out)
 {
-- 
2.49.0

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

[David Hildenbrand]

On 17.09.25 07:59, Lance Yang wrote:
> 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_is_supported() into vm_util.c/h to ensure
> tests are properly skipped when the feature is not enabled.

I'll note that tools/testing/selftests/mm/config contains

	CONFIG_MEM_SOFT_DIRTY=y

But yes, the current arm64 handling is nasty, because some other archs 
(e.g., riscv) also don't support it yet.

LGTM, some nits below:

> 
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Lance Yang <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       | 28 ++++++++++++++++++++++
>   tools/testing/selftests/mm/vm_util.h       |  1 +
>   4 files changed, 35 insertions(+), 20 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/madv_populate.c b/tools/testing/selftests/mm/madv_populate.c
> index b6fabd5c27ed..43dac7783004 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_is_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_is_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..98e42d2ac32a 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_is_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..3173335df775 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -449,6 +449,34 @@ bool check_vmflag_pfnmap(void *addr)
>   	return check_vmflag(addr, "pf");
>   }
>   
> +bool softdirty_is_supported(void)

I'd just call it "softdirty_supported" similar to 
"pagemap_scan_supported()".

> +{
> +	char *addr;
> +	int ret = 0;

bool supported = false;

> +	size_t pagesize;
> +
> +	/* We know for sure that arm64 does not support soft-dirty. */
> +#if defined(__aarch64__)
> +	return ret;
> +#endif

Just drop this arm special case now.

> +	pagesize = getpagesize();

const size_t pagesize = getpagesize();

> +	/*
> +	 * __mmap_complete() always sets VM_SOFTDIRTY for new VMAs, so we
> +	 * just mmap a small region and check its VmFlags in /proc/self/smaps
> +	 * for the "sd" flag.
> +	 */

/* 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");
> +
> +	if (check_vmflag(addr, "sd"))
> +		ret = 1;

supported = true;

> +
> +	munmap(addr, pagesize);
> +	return ret;
> +}
> +

-- 
Cheers

David / dhildenb

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

[Lance Yang]

On 2025/9/17 18:51, David Hildenbrand wrote:
> On 17.09.25 07:59, Lance Yang wrote:
>> 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_is_supported() into vm_util.c/h to 
>> ensure
>> tests are properly skipped when the feature is not enabled.
> 
> I'll note that tools/testing/selftests/mm/config contains
> 
>      CONFIG_MEM_SOFT_DIRTY=y
> 
> But yes, the current arm64 handling is nasty, because some other archs 
> (e.g., riscv) also don't support it yet.

Yep.

> 
> LGTM, some nits below:

Thanks for taking time to review!

> 
>>
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: Lance Yang <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       | 28 ++++++++++++++++++++++
>>   tools/testing/selftests/mm/vm_util.h       |  1 +
>>   4 files changed, 35 insertions(+), 20 deletions(-)
>>
>> diff --git a/tools/testing/selftests/mm/madv_populate.c b/tools/ 
>> testing/selftests/mm/madv_populate.c
>> index b6fabd5c27ed..43dac7783004 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_is_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_is_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..98e42d2ac32a 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_is_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..3173335df775 100644
>> --- a/tools/testing/selftests/mm/vm_util.c
>> +++ b/tools/testing/selftests/mm/vm_util.c
>> @@ -449,6 +449,34 @@ bool check_vmflag_pfnmap(void *addr)
>>       return check_vmflag(addr, "pf");
>>   }
>> +bool softdirty_is_supported(void)
> 
> I'd just call it "softdirty_supported" similar to 
> "pagemap_scan_supported()".

Got it.

> 
>> +{
>> +    char *addr;
>> +    int ret = 0;
> 
> bool supported = false;
> 
>> +    size_t pagesize;
>> +
>> +    /* We know for sure that arm64 does not support soft-dirty. */
>> +#if defined(__aarch64__)
>> +    return ret;
>> +#endif
> 
> Just drop this arm special case now.

OK

> 
>> +    pagesize = getpagesize();
> 
> const size_t pagesize = getpagesize();
> 
>> +    /*
>> +     * __mmap_complete() always sets VM_SOFTDIRTY for new VMAs, so we
>> +     * just mmap a small region and check its VmFlags in /proc/self/ 
>> smaps
>> +     * for the "sd" flag.
>> +     */
> 
> /* New mappings are expected to be marked with VM_SOFTDIRTY (sd). */

Cool. Much better!

> 
>> +    addr = mmap(0, pagesize, PROT_READ | PROT_WRITE,
>> +            MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
>> +    if (!addr)
>> +        ksft_exit_fail_msg("mmap failed\n");
>> +
>> +    if (check_vmflag(addr, "sd"))
>> +        ret = 1;
> 
> supported = true;

I'll adjust as you suggested ;)

> 
>> +
>> +    munmap(addr, pagesize);
>> +    return ret;
>> +}
>> +
> 

Cheers,
Lance