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b=akEmkLS7ZDQTu8lus8F9aGBXvZ+PK9spg1Au2o6EZRbCw2Hw9awxVv2IXe4he/g6H O0WpKNKWzEzJtVnVJK1PDdyTE5P61zauMxJfsTJvY3TUgYj+trQhakmg4bH11KFZnu FEICOjEawjwjjNk/khAhUy6+LffID6T30hh5ePDNQkbnV2LGRpbf8h2YzYDybssBBz w1jUbXibQ+pkh6m6yhH5JT++qvuHb/fxKe6Dtek/VEB+ij0Mj1/dPLSbRNLURc7MPg ZMxBOsKKOsCdx/Go6/W49CkMljZ5xb1jm6aIqhjAb2dzC9mhfjU1d8Oqe8oC2Kuev6 svSPcC3Q5p+mg== Message-ID: <4de1dfb3-b349-4916-9fe0-6b9697583ac7@kernel.org> Date: Mon, 21 Sep 2026 20:59:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] mm: selftests: Adjust the MADV_COLLAPSE uffd-minor selftests To: James Houghton , Andrew Morton Cc: Lorenzo Stoakes , Zi Yan , Baolin Wang , liam@infradead.org, Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Yang Shi , zokeefe@google.com, hughd@google.com, Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260910023411.514987-1-jthoughton@google.com> <20260910023411.514987-2-jthoughton@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260910023411.514987-2-jthoughton@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 42B69100003 X-Stat-Signature: z5bwnx8qmu1maaxiwiabsupcj483fwpa X-HE-Tag: 1790017201-675578 X-HE-Meta: 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 HfYc8bQK lHIGbhaINDdCULztZAIb9ruB4bvzrTzHKkDw6WcmwUpCzV6KXc8Gl76UCwgKk2oCmCMDSJx8I1AgIT65DD4zxFTv4odW3fBvGJj+Y2euCiSfUz785VVSXZqiWEHring8bQawkE8yv33ukBRXY+3R5W++fRHzqlK0kB8gSfvf4Loma0t2/shYAO7cvK5l/xwkBsH62O19Cxt9653XHMmQed+xw4EoSgTxwVGAJtrdlqwJPUt+piEIAO3sNQWf0ln1RDYUwueX/Lix/Pvuj34G43xFcc8Wzbsl5dROALDpEb6D93ez1ZdMaBd9JCTFLMTskbuZXf2o83N8gzNA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/10/26 04:34, James Houghton wrote: > The behavior of MADV_COLLAPSE with uffd-minor VMAs has changed: > MADV_COLLAPSE will no longer install PTEs where none existed before. Misleading: MADV_COLLAPSE installed a PMD not PTEs? > Update the selftest to demonstrate this new behavior. > > On an unpatched kernel, the test will hit "unexpected memory contents > after collapse". > > If the selftest is left unpatched but the kernel is patched, the > selftest will SKIP when it gets EINVAL back from MADV_COLLAPSE. > > Signed-off-by: James Houghton > --- > tools/testing/selftests/mm/uffd-unit-tests.c | 75 ++++++++++++++++++-- > 1 file changed, 68 insertions(+), 7 deletions(-) > > diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c > index ef9b3956bdcf..6f2360f9b75d 100644 > --- a/tools/testing/selftests/mm/uffd-unit-tests.c > +++ b/tools/testing/selftests/mm/uffd-unit-tests.c > @@ -518,19 +518,34 @@ static void uffd_wp_fork_pin_with_event_test(uffd_global_test_opts_t *gopts, uff > uffd_wp_fork_pin_test_common(gopts, args, true); > } > > -static void check_memory_contents(uffd_global_test_opts_t *gopts, char *p) > +static int __check_memory_contents(unsigned long offset, > + unsigned long nr_pages, > + uffd_global_test_opts_t *gopts, > + char *p) Two tabs look better ;) > { > unsigned long i, j; > uint8_t expected_byte; > > - for (i = 0; i < gopts->nr_pages; ++i) { > + if (nr_pages + offset < nr_pages) > + err("overflow in memory check"); > + if (nr_pages + offset > gopts->nr_pages) > + err("out of bounds memory check"); > + > + for (i = offset; i < offset + nr_pages; ++i) { > expected_byte = ~((uint8_t)(i % ((uint8_t)-1))); > for (j = 0; j < gopts->page_size; j++) { > uint8_t v = *(uint8_t *)(p + (i * gopts->page_size) + j); > if (v != expected_byte) > - err("unexpected page contents"); > + return 1; > } > } > + > + return 0; > +} > + > +static int check_memory_contents(uffd_global_test_opts_t *gopts, char *p) > +{ > + return __check_memory_contents(0, gopts->nr_pages, gopts, p); > } > > static void uffd_minor_test_common(uffd_global_test_opts_t *gopts, bool test_collapse, bool test_wp) > @@ -539,6 +554,8 @@ static void uffd_minor_test_common(uffd_global_test_opts_t *gopts, bool test_col > pthread_t uffd_mon; > char c = '\0'; > struct uffd_args args = { 0 }; > + unsigned long checked = 0; > + bool bad_contents; Through in an empty line. Or better struct uffd_args args = { .gopts = gopts }; > > /* > @@ -564,24 +581,65 @@ static void uffd_minor_test_common(uffd_global_test_opts_t *gopts, bool test_col > if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) > err("uffd_poll_thread create"); > > + if (test_collapse) { > + /* > + * Read just a single page and try collapsing. The collapse > + * should either be rejected or be a no-op. > + */ > + if (__check_memory_contents(0, 1, gopts, gopts->area_dst_alias)) > + err("unexpected memory contents before collapse"); > + > + /* MADV_COLLAPSE might return EINVAL for uffd-minor VMAs. */ > + madvise(gopts->area_dst_alias, gopts->nr_pages * gopts->page_size, > + MADV_COLLAPSE); Add an explicit check for expected errnos? > + /* > + * If the above collapse mapped pages that were not explicitly > + * CONTINUE'd, the below __check_memory_contents() will not > + * fault on some pages, resulting in incorrect contents. The > + * PTE for the first page may get retracted, so avoid checking > + * that page, as we might take a second fault, flipping the > + * contents a second time. > + */ > + checked = 1; I'm not an expert on this code. But a trivial check to see whether there is something in the page tables that shouldn't be there is through the help of pagemap_is_populated(). Maybe that would help to simplify things, not sure. -- Cheers, David