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b=Mak/MiUkd+UeBgThN5oJMu2tRhUeTEbSkzhtbgGuJ2abeIXAAhw/WSRG9RVeEr5Jy kectQVA4ZvBcEu5IfC1xcl2LwP70llm2OY6xx5vz6Xh+UlGb2Xnbt1IPCg8wtdV0eI OTXlP7aryLb2yWcL9zFI4WO/BinKkUOtJSWZ/B3OIxZLi1TjEOL1JpMvq6p42u9/EX CwE2XevGvDSUf/bj92fb58e8ppKJuHM2y36R4AVnu97jCsOLCMNT/qtwSAQIRXnJD4 /H1DH/dxGW9Xjzc3PYEpnU8f3hbg6XAdMj47rurWmWWOLfcQRax1QJ3RHZVHR5xIuP 5piDRYPkhSgIw== Message-ID: Date: Wed, 18 Feb 2026 09:01:35 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] mm/huge_memory: fix move_pages_huge_pmd() for huge zero pages To: Chris Down , Andrew Morton Cc: Matthew Wilcox , kernel-team@fb.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C4D9740009 X-Stat-Signature: icr5k97phab6tt7upiobdsacr84usaa9 X-HE-Tag: 1771401700-469899 X-HE-Meta: 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 ssXzooUm Za6QFY+42+VkgqfJ/mRPsXMGqhvVDpln7UmLPdG68nWI2Atu19Hy9dtOkBNpTDVURgiCbQL4XpF5Ezrw1YlqK7Oqd035ec9id5xFlRCvz2GdzmZTjFdW8SAaxgJrLirUphokLloT710Ss7Hs+8GVz5YXIM8HRxHbL434GLNv/pGMawentLSSFfaUiroEUrlUZJ7uszhHH81jwziNjxTOYIPCnQ1n/3NkcwKTj9Iuix2VCY33HzinGvl+XMFylRwq8YzP9e6hDk+duGyq30FcysqYiZlaaY0yMZylvPXEDfPa5OH1PVZDA2EXxWw== 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 2/18/26 04:44, Chris Down wrote: > Two fixes for the huge zero page path in move_pages_huge_pmd() > (UFFDIO_MOVE). > > Patch 1 fixes a use of NULL folio introduced by the folio_mk_pmd() > conversion in commit e3981db444a0 ("mm: add folio_mk_pmd()"). > mk_huge_pmd(src_page, ...) with folio_mk_pmd(src_folio, ...) in the huge > zero page branch where src_folio is explicitly NULL. With > SPARSEMEM_VMEMMAP this silently produces a PMD with a bogus PFN, on > other memory models it is a NULL deref. > > Patch 2 adds the missing pmd_mkspecial() call that was omitted when > commit d82d09e48219 ("mm/huge_memory: mark PMD mappings of the huge zero > folio special") marked huge zero folio PMD mappings as special. Without > it, vm_normal_page_pmd() on CONFIG_ARCH_HAS_PTE_SPECIAL architectures > does not recognise the moved huge zero page as special, incorrectly > treating it as a normal page and corrupting its refcount. Thanks for the report and fixes. This sounds like something selftests should have detected. Can we teach tools/testing/selftests/mm/uffd-unit-tests.c to trigger that behavior on the huge zero folio? We have uffd_move_pmd_test(), but it seems to focus on moving non-zero folios I suppose. -- Cheers, David