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[2003:d8:2f14:2400:afc:9797:137c:a25b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e2aae3d58sm34490655e9.21.2025.09.24.05.49.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 05:49:47 -0700 (PDT) Message-ID: <8006c8c3-8e62-47c2-9d0d-9c7183dcdcf9@redhat.com> Date: Wed, 24 Sep 2025 14:49:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: mte: Do not flag the zero page as PG_mte_tagged To: Lance Yang , Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, Gergely Kovacs , Will Deacon References: <20250924123528.1536835-1-catalin.marinas@arm.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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: M_HS9jj951ZQlWzDmJGSK24HkMICsy7USlZCeyeebxA_1758718189 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: AC7B24000E X-Rspamd-Server: rspam05 X-Stat-Signature: 8a3on81mspkdzqqtsa4nkzazy1w4b5gw X-Rspam-User: X-HE-Tag: 1758718191-991904 X-HE-Meta: U2FsdGVkX18LGmiHAWjz3icPQ2ZozPPywyMzWpL2K0/W54b3Xu8enXWvjbEESqO0444pXxrwbpv4GxgeinQkff+KmQrg5faq0vSUWL0RwfJE1J3Z/rPxtouvJzNOx+TScXONpVlsm/Pyg+PiuJJNNZ+DUmem9Was9H+dsAOBLa22Ny5aauD7ANCxg+KlHL8worWTkMbHgZq2AVBrQ4+NPTFFIZveQBLbuu568OA5KXXt13NH7VD9WM4Tzpin5PXJZOGIu8+C5KWDkAnieSVgqV/vdVI8DNSsRCGSH6Ghpp2CF7ZjSI0UNuytKVSxgCOtfT0CK4tO6ECFTe3qoQPLc0LXmfVJHckqbxr/HDO5Dq5e9864dwk1X/KJoYjItTKZtigeC9/CmK4Yx7uUZuH6sEmrHsmj4asKPU6zloCzy1gr7Y0ZHvpXU5uzqfUBNseqSORYz9UvPlU7m7WJnTQeA3Cmz3UxBIdpqBh90e/bg0iWr0z3HiFfEtUCBX73VBJNgzka6bmLwrAUvaZWnZVlrm90OoMpoyJYmJoL8xuRK2RpyazN/5PiIqk7qyWd/+epvAJxQzZdxOjYJ9IB2cP4dkqRHxUs5YYqibk4Bw72cXTBxH3nKtU3o2rz6E/y6Q10zvopVw7EDlc1wb5akQ0pbF6wuU98o7K+G87M7mKVO4RUcGTwknd99ldlDeZRJbsMC7/fZk4qjm/d5jNUnqRo97IAkeH5hNI19zMcXlacTYVhU3F+T+ILPb/uJofzyXZBvGfC2v+JifB7ClAmaHQqZRGYTqKrcPQ5z//byUwu1nYZJ7jCP5sR4CstCZr3mRgRquhyFPPQrcyflI5reqH8FduC6teMtDiuhkhIUPeNb6SIDeqDaQ82x11aJxOrZvdvkfiPWzBprd6AdwxoBdjKNN7MjYTVZ5BGvTSYnC8cWhKRAtf9Rpk37tOTUYFkYR4vmZdsyI8HAv++N+RtRu4 IRFd6FMZ 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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 24.09.25 14:48, Lance Yang wrote: > > > On 2025/9/24 20:31, Catalin Marinas wrote: >> Commit 68d54ceeec0e ("arm64: mte: Allow PTRACE_PEEKMTETAGS access to the >> zero page") attempted to fix ptrace() reading of tags from the zero page >> by marking it as PG_mte_tagged during cpu_enable_mte(). The same commit >> also changed the ptrace() tag access permission check to the VM_MTE vma >> flag while turning the page flag test into a WARN_ON_ONCE(). >> >> Attempting to set the PG_mte_tagged flag early with >> CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled may either hang (after commit >> d77e59a8fccd "arm64: mte: Lock a page for MTE tag initialisation") or >> have the flags cleared later during page_alloc_init_late(). In addition, >> pages_identical() -> memcmp_pages() will reject any comparison with the >> zero page as it is marked as tagged. >> >> Partially revert the above commit to avoid setting PG_mte_tagged on the >> zero page. Update the __access_remote_tags() warning on untagged pages >> to ignore the zero page since it is known to have the tags initialised. >> >> Note that all user mapping of the zero page are marked as pte_special(). >> The arm64 set_pte_at() will not call mte_sync_tags() on such pages, so >> PG_mte_tagged will remain cleared. >> >> Signed-off-by: Catalin Marinas >> Fixes: 68d54ceeec0e ("arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page") >> Reported-by: Gergely Kovacs >> Cc: # 5.10.x >> Cc: Will Deacon >> Cc: David Hildenbrand >> Cc: Lance Yang >> --- >> >> For reference, discussion on page merging here: >> >> https://lore.kernel.org/r/aNKJ5glToE4hMhWA@arm.com > > Cool. LGTM. > Acked-by: Lance Yang Likely you can provide even a Tested-by? Just saying :) -- Cheers David / dhildenb