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[2003:cb:c700:2400:6b79:2aa:9602:7016]) by smtp.gmail.com with ESMTPSA id n17-20020a5d4c51000000b002d6f285c0a2sm31727959wrt.42.2023.05.02.12.17.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 May 2023 12:17:55 -0700 (PDT) Message-ID: <505b7df8-bb60-7564-af28-b99875eea12a@redhat.com> Date: Tue, 2 May 2023 21:17:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH v7 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings Content-Language: en-US To: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: Jason Gunthorpe , Jens Axboe , Matthew Wilcox , Dennis Dalessandro , Leon Romanovsky , Christian Benvenuti , Nelson Escobar , Bernard Metzler , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Bjorn Topel , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Richard Cochran , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, Oleg Nesterov , Jason Gunthorpe , John Hubbard , Jan Kara , "Kirill A . Shutemov" , Pavel Begunkov , Mika Penttila , Dave Chinner , Theodore Ts'o , Peter Xu , Matthew Rosato , "Paul E . McKenney" , Christian Borntraeger References: From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org > +static bool folio_longterm_write_pin_allowed(struct folio *folio) > +{ > + struct address_space *mapping; > + > + /* > + * GUP-fast disables IRQs - this prevents IPIs from causing page tables > + * to disappear from under us, as well as preventing RCU grace periods > + * from making progress (i.e. implying rcu_read_lock()). > + * > + * This means we can rely on the folio remaining stable for all > + * architectures, both those that set CONFIG_MMU_GATHER_RCU_TABLE_FREE > + * and those that do not. > + * > + * We get the added benefit that given inodes, and thus address_space, > + * objects are RCU freed, we can rely on the mapping remaining stable > + * here with no risk of a truncation or similar race. > + */ > + lockdep_assert_irqs_disabled(); > + > + /* > + * If no mapping can be found, this implies an anonymous or otherwise > + * non-file backed folio so in this instance we permit the pin. > + * > + * shmem and hugetlb mappings do not require dirty-tracking so we > + * explicitly whitelist these. > + * > + * Other non dirty-tracked folios will be picked up on the slow path. > + */ > + mapping = folio_mapping(folio); > + return !mapping || shmem_mapping(mapping) || folio_test_hugetlb(folio); > +} BTW, try_grab_folio() is also called from follow_hugetlb_page(), which is ordinary GUP and has interrupts enabled if I am not wrong. -- Thanks, David / dhildenb