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Mon, 24 Apr 2023 10:49:37 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1pr0Jj-001Vpp-HL; Mon, 24 Apr 2023 14:49:35 -0300 Date: Mon, 24 Apr 2023 14:49:35 -0300 From: Jason Gunthorpe To: Lorenzo Stoakes Cc: Dave Chinner , 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 Subject: Re: [PATCH] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: References: <20230423222941.GR447837@dread.disaster.area> <14c6f0f3-0747-4800-8718-4f109f7321ea@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <14c6f0f3-0747-4800-8718-4f109f7321ea@lucifer.local> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 41B1840016 X-Stat-Signature: c5qtiyoozkkzeqsmostheyododefb7n7 X-Rspam-User: X-HE-Tag: 1682358579-293743 X-HE-Meta: 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 WlBI6ycn lNHNS64fansaS44wf1jYfqAzZ+p2JRJss7/6qVNRAuLRdTURlsk7g8+zuKXwvMY6cNS7m/LLmnyZxeF6b0AuSnNEA9IuXRhKycqbJfMIx7UV4fDDhdip2oxfWApoH7p0VW1Vhio48Jaefih6BVqNxaM8Xex5Vte4JunCLY2SxUrYDB56Hbsd/vpHci6SlRE2SlktoKX1DfY01ItVFPOPHPWd4WaTTL4+H4SNyXPWxTXFrdBg0DqH7X4HwfJr8FNN3RcZUp+q6hugB17KynkbmZClHK5R9Q+lcBdyrmZIdu/GeHMcq78V63q30FMBRx5oJFnEQHVId4W24CxcOVXhvI5LCrzDOjkhkcQrI0WNt9O8yhQArxnjFcqO34wbVFBw6u9xCfnLRflDXTSE= 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 Sun, Apr 23, 2023 at 11:56:48PM +0100, Lorenzo Stoakes wrote: > This warned upon check should in reality not occur, because it implies the > GUP user is trying to do something broken and is _not_ explicitly telling > GUP that it knows it's doing it and can live with the consequences. And on > that basis, is worthy of a warning so we know we have to go put this flag > in that place (and know it is a source of problematic GUP usage), or fix > the caller. It is fine for debugging, but we can't merge user triggerable WARN_ONs.. Since the GUP caller has no idea if userspace might be maliciously passing in a file VMA we can't throw warnings. Jason