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b=Ryr1uyc5yP/JYFWgvjsKT+2rhhWZifPokb2ZTKhhSwbk3itoTBEivaDIZj6NndAoR sTy6b2LkupMAxc5rFehpkbjqkfGOIK1+0VJTeO3B0xu7K7Kaktg8vpRlhKRjkMHU+I I4Ph5lYJzyqydt1ULvEPikXSD6eupUTUiKmz3i1klD3tn6GXk8iZe/ojaxL3LxA/UF RsXSRdN+MrTyWzF3a3ZMv1+ZQ+1zrZ1QNxGD/EZ6i9EgKaQ1QsuxnYbq0a+Wxld9jj 25A0ZRbn9O95WUGGaXfMfVrnugdSC0OhVzh5JfrkiN3hXzwT8sAuq6H28N7ASZ2XKi FWO//HPmJavLw== Message-ID: <67c30e4c-3576-4ded-a71f-b49075ed42e3@kernel.org> Date: Tue, 13 Oct 2026 09:39:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/mm: fix uffd move-pmd test crash on 64K base page systems To: Zenghui Yu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com References: <20261011163527.95988-1-zenghui.yu@linux.dev> 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: <20261011163527.95988-1-zenghui.yu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 8186FC0002 X-Stat-Signature: 5wfqnd673aiozuzjfw83cih8nhbmy7o4 X-HE-Tag: 1791877202-835653 X-HE-Meta: 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 x/1nuW6F aSQkeCU3sXffCA0YDg8lyrt+nEeNDtDcGUqGHr1LEU6yrOZklxopnsf82Be09VUHhuyKVQIARsn05/6uoSIau91uPRJlrtUsrJXiCuyuYPRP+227V2yLIpUosPq1+9HjnXAZMuJ+XomLn77rT6sFKlr0OJuyELn5dtF8JX0A1qzLYwx+nfIgtuSKZ7t9wUIOOQ4kscpLKxbgsgSfbveWdF0w/disZqrOrgFDenPPSEwpwavmnqMSwjZobZ7DyXYuBgU9eb4wYfxSvupZ+ljtSzEjsIql3qDynicXs Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/11/26 18:35, Zenghui Yu wrote: > From: "Zenghui Yu (Huawei)" > > uffd_move_pmd_test()/uffd_move_test_common() splits the test area into > chunks of chunk_size and moves them one by one. On arm64 with 64K base > pages the chunk_size (read_pmd_pagesize()) is 512MB, which is larger than > the whole 32MB (UFFD_TEST_MEM_SIZE) test area: > > step_count = nr_pages / (chunk_size / page_size) == 0 > > Because chunk_size > page_size, the test then aligns both areas up to > 512MB, which points far outside of the 32MB mappings, and decrements > step_count, which underflows to ULONG_MAX. The verification loop then > runs away and the first dereference of area_src faults with a SIGSEGV. > > Skip the test when a single chunk cannot fit into the test area. That leaves 64k untested, though? Why not adjust the chunk size accordingly? -- Cheers, David