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Message-ID: <ff1bb8cd-896f-4c7f-a182-42112f5ac5af@lucifer.local> Date: Tue, 25 Apr 2023 00:26:25 +0100 From: Lorenzo Stoakes <lstoakes@...il.com> To: Jason Gunthorpe <jgg@...dia.com> Cc: Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, Matthew Wilcox <willy@...radead.org>, Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>, Leon Romanovsky <leon@...nel.org>, Christian Benvenuti <benve@...co.com>, Nelson Escobar <neescoba@...co.com>, Bernard Metzler <bmt@...ich.ibm.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, Bjorn Topel <bjorn@...nel.org>, Magnus Karlsson <magnus.karlsson@...el.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Jonathan Lemon <jonathan.lemon@...il.com>, "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Christian Brauner <brauner@...nel.org>, Richard Cochran <richardcochran@...il.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org, netdev@...r.kernel.org, bpf@...r.kernel.org, Oleg Nesterov <oleg@...hat.com> Subject: Re: [PATCH v2] mm/gup: disallow GUP writing to file-backed mappings by default 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
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