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Fri, 28 Apr 2023 08:15:11 -0700 (PDT) Received: from [192.168.1.94] ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id x7-20020a92dc47000000b0032f493364c1sm697858ilq.52.2023.04.28.08.15.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Apr 2023 08:15:10 -0700 (PDT) Message-ID: <447d0270-9c0e-23f4-3c62-33c3eff325af@kernel.dk> Date: Fri, 28 Apr 2023 09:15:08 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings by default Content-Language: en-US To: David Hildenbrand , Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jason Gunthorpe , 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 , David Howells , Christoph Hellwig References: <6b73e692c2929dc4613af711bdf92e2ec1956a66.1682638385.git.lstoakes@gmail.com> From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 70BEF18002F X-Stat-Signature: hn7s6yp1jc5i9m9bpj5x4dixi47djp11 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1682694912-553403 X-HE-Meta: U2FsdGVkX1/30kqNlt3ueEyn99Crc6xTsHsr+vf6Z5jYgdeJHxXkCdpiUGIfZ7jErc4wlgbuNMf7EF6BeYudWKKPbFqVrGn2PsrJgI2UsVedtzma7kbLbdMgYmNeeAwZSqzgMtBo/WoxmnKxg8picVBkkmvPrauyRGep6JgHcQAw1kn/XIgO4nzAam461s+cQm19axn1SkPUXE6Zl4CkzAgsTqjoFs1XRfUkSM7RaYm9KaPeekEZUZCCCFKtP5s/EDQFJy96tblYwqn2oTMw/rBiXC7ny9xBbfbEmC8dNN+StxRidHgEg6XKfwWNfDnuLqL76K0ZT1nOY1qE7sco7Gl/hAYil/vKcOGh4x5jSL54JiwrxLhJvVYPe8xY1OUet5h5/ckhvhldHjGdYjD/VYevVaH5i8ppajwxJg8Csn7EyWC3QksmD6tdTp0ExjXjZW8tUToDI0C0GCh/hs3CDrmCvDU5dDWGXLUKxZdqLKH53FNixw3ZnlgZd+1mVWJ2VfCu7ejKvidem7PzNBhlbNbyOgcBYThISpp/jj4CDqPVXvl55crHjAwtaqYFSlfsZa2PFdwxZJ8gjyyNQTj52ujJzqKokHZg+5rr9L2SdlID0YgJBxCg5HKd94xBl+v8HQbEvVnqxJ2dHxMUoRAJF3EvKvmp8VQOpunC81HJ//tWHhySmy7qKnFszdze8Dh4Un5kgi+6VpQYlrn3dKeE7yBTPTD8uFfNJalLYUerD+IUXvAPr1CsAoWCUHCKBedPFsk8g86YczfUDwSK0HtgOd+goIXycRicPHCzhPF5uuVtzH+9ZGWV2UP/60XxB9E0986QZ0vUmU0udJTIXvvOVU+Qqn+UxQKAJ6kH52a4tvFYfr+cFuJe9qNJ5FclguS8Z/zgiMD60MHoQ4N6tPbip2VHY/4M3N0SsHR8VJ6zdFXIfvE6grHMT5RhmIRnF4AjWfq1hXKWpePxP0RhJbK +SqmfXgG 1ycHLvQ7/LviaY3EHlesWI/iiYgaVhgu33zMqIQeKJQxEgizziUXTteoffk6lkPKEJAd75g307z1HX6jQdDFkqNFk6iNgLiZqaE5pBfnQYAb0XwvN7SdsETHBQ4iq1RewX2CldyGLssh5UUG7+/gLGiBPDV3JvtCQtd//Z8ckoSG/ZC0WAFQDNa9PYSZHXaPMQTk/MVZewV4Q9NLsv6khkGUHKBH//uFTSX5/wzuju3jj2A4OS0gMH2hY8jbyfQQ/aErCDTZUN+nxToZdYaaivs1z+D+qU5qhslbvsbeX7gVIgze80hYRI0B1LI+AY/OTQvQ7FXD+YqlnZrGVlF4sHgf92h4wow1ufaL6khDzmPv3hb/uhot7Icn3mRtRmuC080jj1dd3ajW7LwXgG4ydbWsLpROiSoElzgKSllx5Emf7VKC0Cn7YuTJ07fuHpshGQUylXk/0bF8Sj/E= 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: On 4/28/23 9:13?AM, David Hildenbrand wrote: >>> I know, Jason und John will disagree, but I don't think we want to be very >>> careful with changing the default. >>> >>> Sure, we could warn, or convert individual users using a flag (io_uring). >>> But maybe we should invest more energy on a fix? >> >> This is proactively blocking a cleanup (eliminating vmas) that I believe >> will be useful in moving things forward. I am not against an opt-in option >> (I have been responding to community feedback in adapting my approach), >> which is the way I implemented it all the way back then :) > > There are alternatives: just use a flag as Jason initially suggested > and use that in io_uring code. Then, you can also bail out on the > GUP-fast path as "cannot support it right now, never do GUP-fast". Since I've seen this brougth up a few times, what's the issue on the io_uring side? We already dropped the special vma checking, it's in -git right. Hence I don't believe there are any special cases left for io_uring at all, and we certainly don't allow real file backings either, never have done. -- Jens Axboe