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Message-ID: <20230425101153.xxi4arpwkz7ijnvm@box.shutemov.name> Date: Tue, 25 Apr 2023 13:11:53 +0300 From: "Kirill A . Shutemov" <kirill@...temov.name> To: Lorenzo Stoakes <lstoakes@...il.com> Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Jason Gunthorpe <jgg@...pe.ca>, 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>, Jason Gunthorpe <jgg@...dia.com>, John Hubbard <jhubbard@...dia.com>, Jan Kara <jack@...e.cz>, Pavel Begunkov <asml.silence@...il.com> Subject: Re: [PATCH v3] mm/gup: disallow GUP writing to file-backed mappings by default On Tue, Apr 25, 2023 at 08:14:14AM +0100, Lorenzo Stoakes wrote: > GUP does not correctly implement write-notify semantics, nor does it > guarantee that the underlying pages are correctly dirtied, which could lead > to a kernel oops or data corruption when writing to file-backed mappings. > > This is only relevant when the mappings are file-backed and the underlying > file system requires folio dirty tracking. File systems which do not, such > as shmem or hugetlb, are not at risk and therefore can be written to > without issue. > > Unfortunately this limitation of GUP has been present for some time and > requires future rework of the GUP API in order to provide correct write > access to such mappings. > > In the meantime, we add a check for the most broken GUP case - > FOLL_LONGTERM - which really under no circumstances can safely access > dirty-tracked file mappings. > > Suggested-by: Jason Gunthorpe <jgg@...dia.com> > Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com> > --- > v3: > - Rebased on latest mm-unstable as of 24th April 2023. > - Explicitly check whether file system requires folio dirtying. Note that > vma_wants_writenotify() could not be used directly as it is very much focused > on determining if the PTE r/w should be set (e.g. assuming private mapping > does not require it as already set, soft dirty considerations). Hm. Okay. Have you considered having a common base for your case and vma_wants_writenotify()? Code duplication doesn't look good. -- Kiryl Shutsemau / Kirill A. Shutemov
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