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[2003:cb:c707:3900:757e:83f8:a99d:41ae]) by smtp.gmail.com with ESMTPSA id l8-20020a1c7908000000b003f506e6ff83sm1421875wme.22.2023.05.17.01.30.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 May 2023 01:30:21 -0700 (PDT) Message-ID: Date: Wed, 17 May 2023 10:30:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH 1/3] mm: Move arch_do_swap_page() call to before swap_free() 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 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-Rspam-User: X-Stat-Signature: 3w8nrsjo9rkm6pckbyg8cxysk3zrfmw3 X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5D57F4001E X-HE-Tag: 1684312227-23514 X-HE-Meta: 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 ctBkA5c/ uEEqMlkgOO8hNUGuqVIdWFa+FAhgLZx9G2v+7QlHHhzWEJrXi0MPfPSy22lxFDyysVvKYdWIayjdGaoYpMcoqbcBiM1EUL31dFk6Q60/+CFP3KLoNwpmXdm9rjzxQMgZ75VJw8RESHlebitpvtLcFkL+9JVxYfvWF4g1mdDLXh9aONQZevkcQV5LPevBXE3l0UsvcWH4JefQFhVDzwkYKwIaob2vNUiicE2tPoLXYZLrz6KfUgTD/RnLOOZOA+Gm3PAlRbwMtuevs18krX/aZ4t5BOqtzMY0irdQQc+NjTPNfXql80R6pbTIJHXTDnDOGGl4OD3aoEFQwA8bLe52ok74kyksUu4Pz9BvyfwTQ0cZS7fRoDJvDxxfkK/CMLYpT5N0LGWvAMly9mZpvwCOwCVVRYTkg5GgMwiXbxAMmHsn44bROLwB42vm5370WtloWQekouidy/Mst2p+K9WXISJF2wg== 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: >> Would the idea be to fail swap_readpage() on the one that comes last, >> simply retrying to lookup the page? > > The idea would be that T2's arch_swap_readpage() could potentially not > find tags if it ran after swap_free(), so T2 would produce a page > without restored tags. But that wouldn't matter, because T1 reaching > swap_free() means that T2 will follow the goto at [1] after waiting > for T1 to unlock at [2], and T2's page will be discarded. Ah, right. > >> This might be a naive question, but how does MTE play along with shared >> anonymous pages? > > It should work fine. shmem_writepage() calls swap_writepage() which > calls arch_prepare_to_swap() to write the tags. And > shmem_swapin_folio() has a call to arch_swap_restore() to restore > them. 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. -- Thanks, David / dhildenb