From: Li Wang Date: Tue, 24 Jun 2025 04:24:11 +0000 (+0800) Subject: selftests/mm: fix UFFDIO_API usage with proper two-step feature negotiation X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=98db4b5472ed8a64e418b895054c5fb123c038bf;p=thirdparty%2Fkernel%2Flinux.git selftests/mm: fix UFFDIO_API usage with proper two-step feature negotiation 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. [liwang@redhat.com: fail the test if sys_userfaultfd() fails, per David] Link: https://lkml.kernel.org/r/20250625004645.400520-1-liwang@redhat.com Link: https://lkml.kernel.org/r/20250624042411.395285-1-liwang@redhat.com Signed-off-by: Li Wang Suggested-by: David Hildenbrand Acked-by: David Hildenbrand Cc: Aruna Ramakrishna Cc: Bagas Sanjaya Cc: Catalin Marinas Cc: Dave Hansen Cc: Joey Gouly Cc: Johannes Weiner Cc: Keith Lucas Cc: Ryan Roberts Cc: Shuah Khan Cc: Axel Rasmussen Cc: Li Wang Cc: Mike Rapoport Cc: Nadav Amit Cc: Peter Xu Signed-off-by: Andrew Morton --- diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c index b61803e36d1cf..d8bd1911dfc0a 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_fail("__NR_userfaultfd failed\n"); + goto unmap; + } + + /* Now, enable it ("two-step handshake") */ + uffdio_api.api = UFFD_API; + uffdio_api.features = UFFD_FEATURE_PAGEFAULT_FLAG_WP; + if (ioctl(uffd, UFFDIO_API, &uffdio_api) < 0) { + ksft_test_result_fail("UFFDIO_API failed: %s\n", strerror(errno)); + goto close_uffd; + } + /* Register UFFD-WP, no need for an actual handler. */ if (uffd_register(uffd, map, size, false, true, false)) { ksft_test_result_fail("UFFDIO_REGISTER_MODE_WP failed\n");