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[2003:d8:2f4e:fd00:8e13:e3b5:90c8:1159]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453647082a2sm103293925e9.37.2025.06.23.01.33.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jun 2025 01:33:33 -0700 (PDT) Message-ID: Date: Mon, 23 Jun 2025 10:33:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/selftests: improve UFFD-WP feature detection in KSM test To: Li Wang , akpm@linux-foundation.org, 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 References: <20250622081035.378164-1-liwang@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250622081035.378164-1-liwang@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: iU3bqbaA6zh4AjmORG18F7Orrt14uJwTlsfd_YmLVtQ_1750667614 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1416740010 X-Stat-Signature: rxxiz9etzrogz5hqt1ts8r5nsb8pezbd X-HE-Tag: 1750667619-986344 X-HE-Meta: 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 BO3zUWBR 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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: On 22.06.25 10:10, 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 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 > Cc: Aruna Ramakrishna > Cc: Bagas Sanjaya > Cc: Catalin Marinas > Cc: Dave Hansen > Cc: David Hildenbrand > Cc: Joey Gouly > Cc: Johannes Weiner > Cc: Keith Lucas > Cc: Ryan Roberts > Cc: Shuah Khan > --- > 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)) { The man page (man UFFDIO_API) documents: Since Linux 4.11, applications should use the features field to perform a two-step handshake. First, UFFDIO_API is called with the features field set to zero. The kernel responds by setting all supported feature bits. Applications which do not require any specific features can begin using the userfaultfd immedi‐ ately. Applications which do need specific features should call UFFDIO_API again with a subset of the reported feature bits set to enable those features. So likely, what you want in this patch here is something like: diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c index b61803e36d1cf..5cf819ac958d0 100644 --- a/tools/testing/selftests/mm/ksm_functional_tests.c +++ b/tools/testing/selftests/mm/ksm_functional_tests.c @@ -393,7 +393,7 @@ 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"); goto close_uffd; @@ -403,6 +403,14 @@ static void test_unmerge_uffd_wp(void) goto close_uffd; } + /* 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\n"); + 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"); -- Cheers, David / dhildenb