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[2003:d8:2f42:b000:db8b:7655:f60f:812b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e760711bb9sm1533593f8f.0.2025.09.11.01.12.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Sep 2025 01:12:49 -0700 (PDT) Message-ID: Date: Thu, 11 Sep 2025 10:12:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: avoid poison consumption when splitting THP To: Andrew Zaborowski , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Andrew Morton , Lorenzo Stoakes , Miaohe Lin References: <20250911021401.734817-1-balrogg+code@gmail.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: <20250911021401.734817-1-balrogg+code@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: pPMK7pw5qk6IzKI5ZwI8hCrvU0K497UJMIxdcsXjIgs_1757578371 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 00CFD40003 X-Rspamd-Server: rspam05 X-Stat-Signature: 7tbugsi5385nx66rhdsz8hdbnptnb8dn X-Rspam-User: X-HE-Tag: 1757578373-105907 X-HE-Meta: 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 5vBluxfc 7itJvs8tA2Pof1KLdaYCbY0rC6QBp46QN5ZLIxIywo78vYlwSMQflIGu90tUHVk2+VSD1n/rDDrOyOM4opKTjdWIpkXO0ihx2+/0Y/HM1rX7jj4wmWSEX5h1CKSG46M4OBj9IPjHYaskIChN2rrUHnR+NNiRyqMtIEOGgXbqxa8tHmeMd1v1yZjcewizkuD731hIz6cPEduc2bshEriHMbcS0Lhg5NofoyZYJr4VfAD5AJ64h7nNbE5sww7pghwp7A1mssNfvv+WvLfS01BgN3qQ1eHvzIr6hPZ7tUuIrFAPl7zTw3tdChR1h7V056w9HA237/AyM+SdNLZfItjJIActZfC42m3gtHw4OElkNtZyhgq/9wuXpyKV8HzMpjjmAvwgPkgck5DVh0FLMX86ox/kZ2fy1f7RS0GK0ZzFjPAqvgAiEE+POIlNLR0CeMSJQghdx 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 11.09.25 04:14, Andrew Zaborowski wrote: > Handling a memory failure pointing inside a huge page requires splitting > the page. The splitting logic uses a mechanism, implemented in > migrate.c:try_to_map_unused_to_zeropage(), that inspects contents of > individual pages to find zero-filled pages. The read access to the > contents may cause a new, synchronous exception like an x86 Machine > Check, delivered before the initial memory_failure() finishes, ending > in a crash. > > Luckily memory_failure() already sets the has_hwpoisoned flag on the > folio right before try_to_split_thp_page(). Don't enable the shared > zeropage mechanism (RMP_USE_SHARED_ZEROPAGE flag) down in > __split_unmapped_folio() when the original folio has has_hwpoisoned. > > Note: we're disabling a potentially useful feature, some of the > individual pages that aren't poisoned might be zero-filled. One > argument for not trying to add a mechanism to maybe re-scan them later, > apart from code cost, is that the owning process is likely being > killed and the memory released. > > Signed-off-by: Andrew Zaborowski > --- I would suggest just checking whether the page (PageHWPoison()) is poisoned before doing the check for zero. If set, just treat it as non-zero. No need to stop the split. You'll have to do that in two locations. No need to mess with RMP_USE_SHARED_ZEROPAGE -- Cheers David / dhildenb