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Tue, 24 Jun 2025 20:47:02 -0400 X-MC-Unique: RtPIR-3xNLaq7N9N4sbElg-1 X-Mimecast-MFC-AGG-ID: RtPIR-3xNLaq7N9N4sbElg_1750812420 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 739E6180028D; Wed, 25 Jun 2025 00:46:59 +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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E8D5C19560A3; Wed, 25 Jun 2025 00:46:50 +0000 (UTC) From: Li Wang To: akpm@linux-foundation.org, david@redhat.com, peterx@redhat.com, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Nadav Amit , Aruna Ramakrishna , Bagas Sanjaya , Catalin Marinas , Dave Hansen , Joey Gouly , Johannes Weiner , Keith Lucas , Ryan Roberts , Shuah Khan Subject: [PATCH v3] selftests/mm: Fix UFFDIO_API usage with proper two-step feature negotiation Date: Wed, 25 Jun 2025 08:46:45 +0800 Message-ID: <20250625004645.400520-1-liwang@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 X-Stat-Signature: qnwr35knchpik636pd6jkybbmxbd7p9m X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A8CCBC0006 X-Rspam-User: X-HE-Tag: 1750812426-875423 X-HE-Meta: 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 WPfMkqhW 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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: Peter Xu Cc: Nadav Amit 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 Acked-by: David Hildenbrand --- .../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..d8bd1911dfc0 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"); -- 2.49.0