linux-kernel - [PATCH] mm/selftests: improve UFFD-WP feature detection in KSM test

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Message-ID: <20250622081035.378164-1-liwang@redhat.com>
Date: Sun, 22 Jun 2025 16:10:35 +0800
From: Li Wang <liwang@...hat.com>
To: akpm@...ux-foundation.org,
	linux-kselftest@...r.kernel.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>,
	Bagas Sanjaya <bagasdotme@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	Joey Gouly <joey.gouly@....com>,
	Johannes Weiner <hannes@...xchg.org>,
	Keith Lucas <keith.lucas@...cle.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Shuah Khan <shuah@...nel.org>
Subject: [PATCH] mm/selftests: improve UFFD-WP feature detection in KSM test

The current implementation of test_unmerge_uffd_wp() explicitly sets
`uffdio_api.features = UFFD_FEATURE_PAGEFAULT_FLAG_WP` before calling
UFFDIO_API. This can cause the ioctl() call to fail with EINVAL on kernels
that do not support UFFD-WP, leading the test to fail unnecessarily:

  # ------------------------------
  # running ./ksm_functional_tests
  # ------------------------------
  # TAP version 13
  # 1..9
  # # [RUN] test_unmerge
  # ok 1 Pages were unmerged
  # # [RUN] test_unmerge_zero_pages
  # ok 2 KSM zero pages were unmerged
  # # [RUN] test_unmerge_discarded
  # ok 3 Pages were unmerged
  # # [RUN] test_unmerge_uffd_wp
  # not ok 4 UFFDIO_API failed     <-----
  # # [RUN] test_prot_none
  # ok 5 Pages were unmerged
  # # [RUN] test_prctl
  # ok 6 Setting/clearing PR_SET_MEMORY_MERGE works
  # # [RUN] test_prctl_fork
  # # No pages got merged
  # # [RUN] test_prctl_fork_exec
  # ok 7 PR_SET_MEMORY_MERGE value is inherited
  # # [RUN] test_prctl_unmerge
  # ok 8 Pages were unmerged
  # Bail out! 1 out of 8 tests failed
  # # Planned tests != run tests (9 != 8)
  # # Totals: pass:7 fail:1 xfail:0 xpass:0 skip:0 error:0
  # [FAIL]

This patch improves compatibility and error handling by:

1. Changes the feature check to first query supported features (features=0)
   rather than specifically requesting WP support.

2. Gracefully skipping the test if:
   - UFFDIO_API fails with EINVAL (feature not supported), or
   - UFFD_FEATURE_PAGEFAULT_FLAG_WP is not advertised by the kernel.

3. Providing better diagnostics by distinguishing expected failures (e.g.,
   EINVAL) from unexpected ones and reporting them using strerror().

The updated logic makes the test more robust across different kernel versions
and configurations, while preserving existing behavior on systems that do
support UFFD-WP.

Signed-off-by: Li Wang <liwang@...hat.com>
Cc: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
Cc: Bagas Sanjaya <bagasdotme@...il.com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Joey Gouly <joey.gouly@....com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Keith Lucas <keith.lucas@...cle.com>
Cc: Ryan Roberts <ryan.roberts@....com>
Cc: Shuah Khan <shuah@...nel.org>
---
 tools/testing/selftests/mm/ksm_functional_tests.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index b61803e36d1c..f3db257dc555 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -393,9 +393,13 @@ static void test_unmerge_uffd_wp(void)
 
 	/* See if UFFD-WP is around. */
 	uffdio_api.api = UFFD_API;
-	uffdio_api.features = UFFD_FEATURE_PAGEFAULT_FLAG_WP;
+	uffdio_api.features = 0;
 	if (ioctl(uffd, UFFDIO_API, &uffdio_api) < 0) {
-		ksft_test_result_fail("UFFDIO_API failed\n");
+		if (errno == EINVAL)
+			ksft_test_result_skip("UFFDIO_API not supported (EINVAL)\n");
+		else
+			ksft_test_result_fail("UFFDIO_API failed: %s\n", strerror(errno));
+
 		goto close_uffd;
 	}
 	if (!(uffdio_api.features & UFFD_FEATURE_PAGEFAULT_FLAG_WP)) {
-- 
2.49.0