On 24.06.25 06:24, Li Wang wrote:
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 robustness of the UFFD-WP test (test_unmerge_uffd_wp) by correctly implementing the UFFDIO_API two-step handshake as recommended by the userfaultfd(2) man page. Key changes: 1. Use features=0 in the initial UFFDIO_API call to query supported feature bits, rather than immediately requesting WP support. 2. Skip the test gracefully if: - UFFDIO_API fails with EINVAL (e.g. unsupported API version), or - UFFD_FEATURE_PAGEFAULT_FLAG_WP is not advertised by the kernel. 3. Close the initial userfaultfd and create a new one before enabling the required feature, since UFFDIO_API can only be called once per fd. 4. Improve diagnostics by distinguishing between expected and unexpected failures, using strerror() to report errors. This ensures the test behaves correctly across a wider range of kernel versions and configurations, while preserving the intended behavior on kernels that support UFFD-WP. Suggestted-by: David Hildenbrand <da...@redhat.com> Signed-off-by: Li Wang <liw...@redhat.com> Cc: Aruna Ramakrishna <aruna.ramakris...@oracle.com> Cc: Bagas Sanjaya <bagasdo...@gmail.com> Cc: Catalin Marinas <catalin.mari...@arm.com> Cc: Dave Hansen <dave.han...@linux.intel.com> Cc: Joey Gouly <joey.go...@arm.com> Cc: Johannes Weiner <han...@cmpxchg.org> Cc: Keith Lucas <keith.lu...@oracle.com> Cc: Ryan Roberts <ryan.robe...@arm.com> Cc: Shuah Khan <sh...@kernel.org> --- Notes: v1 --> v2: * Close the original userfaultfd and open a new one before enabling features * Reworked UFFDIO_API negotiation to follow the official two-step handshake .../selftests/mm/ksm_functional_tests.c | 28 +++++++++++++++++-- 1 file changed, 26 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..19e5b741893a 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("The API version requested is not supported\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)) { @@ -403,6 +407,26 @@ static void test_unmerge_uffd_wp(void) goto close_uffd; }+ /*+ * UFFDIO_API must only be called once to enable features. + * So we close the old userfaultfd and create a new one to + * actually enable UFFD_FEATURE_PAGEFAULT_FLAG_WP. + */ + close(uffd); + uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK); + if (uffd < 0) { + ksft_test_result_skip("__NR_userfaultfd failed\n");
If it now suddenly fails (after it working above), this sure is a fail, right?
Apart from that Acked-by: David Hildenbrand <da...@redhat.com> -- Cheers, David / dhildenb
