Re: [PATCH 2/2] selftests/mm: test a uffd write-protect range with an unregistered page

[Mike Rapoport]

Hi Umang,

On Mon, Nov 02, 2026 at 04:06:21PM +0530, Umang Pokhriyal wrote:
> Register only the first of two pages and check that UFFDIO_WRITEPROTECT
> over both pages fails with ENOENT without changing the first page, when
> protecting and when unprotecting.

I don't think it's worth keeping the test for a regression we already
fixed.
 
> Signed-off-by: Umang Pokhriyal <umangpokhriyall@xxxxxxxxx>
> ---
>  tools/testing/selftests/mm/uffd-unit-tests.c | 56 ++++++++++++++++++++
>  1 file changed, 56 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> index 298609544..57e442fd2 100644
> --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> @@ -375,6 +375,56 @@ static void uffd_wp_unpopulated_test(uffd_global_test_opts_t *gopts, uffd_test_a
>  	uffd_test_pass();
>  }
>  
> +/*
> + * UFFDIO_WRITEPROTECT over a range whose second page is not registered must
> + * fail without changing the first page, in both directions.
> + */
> +static void uffd_wp_partial_range_test(uffd_global_test_opts_t *gopts,
> +				       uffd_test_args_t *args)
> +{
> +	struct uffdio_writeprotect prms = {
> +		.range.start = (uint64_t)gopts->area_dst,
> +		.range.len = 2 * gopts->page_size,
> +	};
> +	uint64_t value;
> +	int pagemap_fd;
> +
> +	/* Only the first page is registered; the second is a separate VMA */
> +	if (uffd_register(gopts->uffd, gopts->area_dst, gopts->page_size,
> +			  false, true, false))
> +		err("register failed");
> +
> +	pagemap_fd = pagemap_open();
> +	*gopts->area_dst = 1;
> +
> +	prms.mode = UFFDIO_WRITEPROTECT_MODE_WP;
> +	if (!ioctl(gopts->uffd, UFFDIO_WRITEPROTECT, &prms) || errno != ENOENT) {
> +		uffd_test_fail("protect over an unregistered page did not fail with ENOENT");
> +		goto out;
> +	}
> +	value = pagemap_get_entry(pagemap_fd, gopts->area_dst);
> +	if (value & PM_UFFD_WP) {
> +		uffd_test_fail("failed protect changed the first page");
> +		goto out;
> +	}
> +
> +	wp_range(gopts->uffd, (uint64_t)gopts->area_dst, gopts->page_size, true);
> +	prms.mode = 0;
> +	if (!ioctl(gopts->uffd, UFFDIO_WRITEPROTECT, &prms) || errno != ENOENT) {
> +		uffd_test_fail("unprotect over an unregistered page did not fail with ENOENT");
> +		goto out;
> +	}
> +	value = pagemap_get_entry(pagemap_fd, gopts->area_dst);
> +	if (!(value & PM_UFFD_WP)) {
> +		uffd_test_fail("failed unprotect changed the first page");
> +		goto out;
> +	}
> +
> +	uffd_test_pass();
> +out:
> +	close(pagemap_fd);
> +}
> +
>  static void uffd_wp_fork_test_common(uffd_global_test_opts_t *gopts, uffd_test_args_t *args,
>  				     bool with_event)
>  {
> @@ -2403,6 +2453,12 @@ uffd_test_case_t uffd_tests[] = {
>  		.uffd_feature_required =
>  		UFFD_FEATURE_PAGEFAULT_FLAG_WP | UFFD_FEATURE_WP_UNPOPULATED,
>  	},
> +	{
> +		.name = "wp-partial-range",
> +		.uffd_fn = uffd_wp_partial_range_test,
> +		.mem_targets = MEM_ANON,
> +		.uffd_feature_required = UFFD_FEATURE_PAGEFAULT_FLAG_WP,
> +	},
>  	{
>  		.name = "minor",
>  		.uffd_fn = uffd_minor_test,
> -- 
> 2.53.0
> 

-- 
Sincerely yours,
Mike.