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[86.156.84.164]) by smtp.gmail.com with ESMTPSA id p13-20020a7bcc8d000000b003ee63fe5203sm13343552wma.36.2023.04.24.16.26.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Apr 2023 16:26:26 -0700 (PDT) Date: Tue, 25 Apr 2023 00:26:25 +0100 From: Lorenzo Stoakes To: Jason Gunthorpe Cc: Christoph Hellwig , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , 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 Subject: Re: [PATCH v2] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: References: <4f16b1fc-6bc5-4e41-8e94-151c336fcf69@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 2F28010001A X-Stat-Signature: 65uj8azjuqjq83j4a5wm4xbu8ee1iktg X-Rspam-User: X-HE-Tag: 1682378788-948886 X-HE-Meta: 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 GVY/k6bj mVXeQspQzNZ/XEbCLa8VBu6BSB0VNTsDaVS1OaMqiQOpigA9OOm0nRoNiApxzMThQTNzNozXm2+1s1SfeXmbeld8ooDFjF/ga3KM6u10FaoMuaf76V3gAR1zePKngzagperpa8p0rRuAplIUkahISfK+3HlO7cuS0uVxxtMc7jjuNVbQZx2z/+1BjzHJLQH68KouUmK9yGVWghMiKF2mPvc2MdMjzzwI5FLe1xinfqFB23csmoC+XVsufK9hRIBs0I/3PAFE1LIx/1MFL9449RBVEEAVKjPoHnClHIyT7nppqgboBHZGtZhlEoGKmMMu4SpDZ8mAozUI9vfoPc4mOZ5Eb/AtOEbHLetusMhHHS/DW1mfvcYc1giSFpAUGeaxUAN2LzNr/KEbe/7Fk1b3q82uCnxlzPXMQRbF5pFtcQPL+NgjGZtW2vVMIkxj5LdZChMftZoSqEIlmXOM= 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 Mon, Apr 24, 2023 at 08:17:11PM -0300, Jason Gunthorpe wrote: > On Tue, Apr 25, 2023 at 12:03:34AM +0100, Lorenzo Stoakes wrote: > > > Except you dirty a page that is mapped elsewhere that thought everything > > was cleaned and... not sure the PTLs really help you much? > > If we have a writable PTE then while the PTE's PTL is held it is impossible > for a FS to make the page clean as any cleaning action has to also > take the PTL to make the PTE non-present or non-writable. > That's a very good point! Passing things back with a spinlock held feels pretty icky though, and obviously a no-go for a FOLL_PIN. Perhaps for a FOLL_GET this would be workable. > > If we want to be more adventerous the opt-in variant could default to on > > for FOLL_LONGTERM too, but that discussion can be had over on that patch > > series. > > I think you should at least do this too to explain why io_uring code > is moving into common code.. > OK, I'll respin this as a v3 of this series then since we'll be defaulting FOLL_LONGTERM at least (for which there seems to be broad consensus), but also permit this flag to be set manually and set it for io_uring. > Jason