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[2003:cb:c722:9d00:7421:54d8:9227:a3e8]) by smtp.gmail.com with ESMTPSA id m16-20020a7bce10000000b003f435652aaesm1753343wmc.11.2023.05.19.02.21.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 19 May 2023 02:21:36 -0700 (PDT) Message-ID: <80f45fec-3e91-c7b3-7fb4-1aa9355c627a@redhat.com> Date: Fri, 19 May 2023 11:21:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 To: Peter Collingbourne Cc: Catalin Marinas , =?UTF-8?B?UXVuLXdlaSBMaW4gKOael+e+pOW0tCk=?= , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "surenb@google.com" , =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= , "kasan-dev@googlegroups.com" , =?UTF-8?B?S3Vhbi1ZaW5nIExlZSAo5p2O5Yag56mOKQ==?= , =?UTF-8?B?Q2FzcGVyIExpICjmnY7kuK3mpq4p?= , "gregkh@linuxfoundation.org" , vincenzo.frascino@arm.com, Alexandru Elisei , will@kernel.org, eugenis@google.com, Steven Price , stable@vger.kernel.org References: <20230512235755.1589034-1-pcc@google.com> <20230512235755.1589034-2-pcc@google.com> <7471013e-4afb-e445-5985-2441155fc82c@redhat.com> <851940cd-64f1-9e59-3de9-b50701a99281@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH 1/3] mm: Move arch_do_swap_page() call to before swap_free() In-Reply-To: X-Mimecast-Spam-Score: 0 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: E233040018 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: mb3o7reu33p58jnii3e85jyw3ye6ofcw X-HE-Tag: 1684488100-374374 X-HE-Meta: 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 KHFvyFcf cCZzyjENuqe5obXAUsy7n0qhaBpnl8cASBRtXlwrn8BCm0bnU0grvyT7gYhLFt4jQ+9BINJxZ1uZN9To1QbmH0M76kA2svwb+hhGr5eB14gjLKjUTSG5uAccfy0zkWSrEOdRymKdqFQRByobGIxzODqs1YAKjAK40SP3WE9h5IfU1qyKA9UDNj/p1L8E1Bvel1YQywGML6ImhQkf3EJ/zOEueUS/lLtoQfnvlzI6STkA3Lu+W1RVbjx0t3C6STcx7tb9pYeOUAn16M84Ntq/L83lpe9uWYTp86S4mQBn5+Nfyf8dUxyW8YMeMiR4zBlRufE5hJMBU2PP2codFKgEUQVByHFQY0iB8W90N8UScdld/tkHG6tQv6dNSehRtvhUJ3PC/rz//Ppji+iemsHoqsN/0njVEr9I15HliQg2O8WObrIoTIoN8fx7KX+qsRmrYogLH5rrnI4KyFGINflJeSAflWg== 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: >> Sorry, I meant actual anonymous memory pages, not shmem. Like, anonymous >> pages that are COW-shared due to fork() or KSM. >> >> How does MTE, in general, interact with that? Assume one process ends up >> modifying the tags ... and the page is COW-shared with a different >> process that should not observe these tag modifications. > > Tag modifications cause write faults if the page is read-only, so for > COW shared pages we would end up copying the page in the usual way, > which on arm64 would copy the tags as well via the copy_highpage hook > (see arch/arm64/mm/copypage.c). Oh, that makes sense, thanks for pointing that out! ... and I can spot that KSM also checks the tag when de-duplicating: pages_identical() ends up calling memcmp_pages(), which knows how to deal with tags. Interestingly, calc_checksum() does not seem to care about tags. But that simply implies that pages with the same content have same checksum, independent of the tag. And pages_identical() is the single source of truth. -- Thanks, David / dhildenb