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Tue, 24 Jun 2025 00:24:27 -0400 X-MC-Unique: X91ThBiuNuuWH4MFPuSUfg-1 X-Mimecast-MFC-AGG-ID: X91ThBiuNuuWH4MFPuSUfg_1750739065 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2E6DA180034E; Tue, 24 Jun 2025 04:24:24 +0000 (UTC) Received: from dell-per7425-02.rhts.eng.pek2.redhat.com (dell-per7425-02.rhts.eng.pek2.redhat.com [10.73.116.18]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0084B18003FC; Tue, 24 Jun 2025 04:24:16 +0000 (UTC) From: Li Wang To: akpm@linux-foundation.org, david@redhat.com, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Aruna Ramakrishna , Bagas Sanjaya , Catalin Marinas , Dave Hansen , Joey Gouly , Johannes Weiner , Keith Lucas , Ryan Roberts , Shuah Khan Subject: [PATCH v2] selftests/mm: Fix UFFDIO_API usage with proper two-step feature negotiation Date: Tue, 24 Jun 2025 12:24:11 +0800 Message-ID: <20250624042411.395285-1-liwang@redhat.com> In-Reply-To: <20250622081035.378164-1-liwang@redhat.com> References: <20250622081035.378164-1-liwang@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Rspamd-Queue-Id: CAF494000D X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: mo9nj1ejm7uknygg1mmt4qc3miwnqffh X-HE-Tag: 1750739073-804066 X-HE-Meta: U2FsdGVkX193MdWJQhutuvqp5nZMXWaCsht/QcPyQSY7D7YljdPqv0Fsgw5rMtszAjP3n1Ogyf2jNu0h7ETN9F05IdpcHQw7pC/dN3KyMn0EuFvCesnoLI+4t3ymJZxglsoBmLRh6FINWT2nQ4ylskr07ArLisjoftthjSxj3A1hri3rEwGPBVFoMz6gLBtxQ74XLWGLtTXlkHb8AXlO4UWhUHJuPAaSSzBZRzEKEGDecUejOvjbvp07sy8gsVxfyFzXk+rikQrxKOMol1HneRnl1LPG8uITO0BzLzEmuDBw7lXIMgQL/fPdQQM1S0CaEBNHiNT5wj/d/2KEu6APRAxNfr0dKhAG6p5UpMDgGT6qIyrx2jkDN+6hcPTaPudh8ZCfPy2wsgkkaewDBIbLNXMbllb5hjMqEiBGWqxMI1yPr2GCfHIQ1kYiwz/55y/1pHX49BbEHiNL3so89iDXEMapbmd3BNp1GLYIpescjPFEhGWjsbMTWiFwMsFEQz+Hu2M6ccL57qUE0FfhvsmvGCCxAJlrp8X1/IuEVZGOUbcURbz0Av7cdL2V6/shsds2glYTNVnpBecspatkPIXWCPuCx3B7BE1JQi20sJjOR4Rxq/vRprejTM700AwT4BoTHvkU2DG6yZrVMFaC45i/D9SDhVgCAqR/ErP9p2Z/zXUDCAJxehAkHbg8dDN9fJG196w7zKcXDVarkATfSG+dFpxBH58cdcgncmqb9x+RGb83c3tNJkuR/s3phprPLQoVap8/hVeTSYQipzNKat1tlz7+pcL6KLCGp20DEBHdKLRRoBnTdvIFJD7rFKW5jzYYwexP3t+NNvx1QO4BLW3ngCZPaxHxWB+juyB6xGStDnQDvGnRZKp3BATKwqe6smbrMjmbu2vxLC437d/k+8kIFX8APK0WLAQMjUgxkx2eFAcxNqilQ94Nxe2WIJz6vOQLQzUt7w+mhhm5ttpnost u4hSZT2S 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 Signed-off-by: Li Wang 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 --- 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"); + 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"); -- 2.49.0