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Tue, 25 Apr 2023 06:11:57 -0400 (EDT) Received: by box.shutemov.name (Postfix, from userid 1000) id F3F9D10BAC9; Tue, 25 Apr 2023 13:11:53 +0300 (+03) Date: Tue, 25 Apr 2023 13:11:53 +0300 From: "Kirill A . Shutemov" To: Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jason Gunthorpe , 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 , Jason Gunthorpe , John Hubbard , Jan Kara , Pavel Begunkov Subject: Re: [PATCH v3] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: <20230425101153.xxi4arpwkz7ijnvm@box.shutemov.name> References: <23c19e27ef0745f6d3125976e047ee0da62569d4.1682406295.git.lstoakes@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <23c19e27ef0745f6d3125976e047ee0da62569d4.1682406295.git.lstoakes@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: c57ukkb6esh1xzbah1gijxqxpg7hmoiu X-Rspamd-Queue-Id: 7F8E41C000C X-HE-Tag: 1682417528-79385 X-HE-Meta: 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 rE9s2l3O g6sMGbrI6CkJAppNHpVxRzESqfJ0DfqojApZAKH0Iz20kZM4N3z94UtVrSWRuuQKtgWZ/RptFxNUuo4Nd7ernhTolD7g6/a756LkLopTOqOFcoOCqlKfyOd+hzgus86uAggA01YQ6OX6WZcp3qhT9YkzYvVP4lO+yj5MSV24ZzmpU372z5ImAT4/697e96QqnIKgE9hkC6nXdnUMD6seTZpx7Jby1ddWkFjPrkfDltg12M4D9WJa0N4Lte5VlvedcX3pRuySNGAHtBnrEOC007AOAKk1VRx7gQmskYjOIz/V0/2Ix8JMwHqoZGodwQSAIUi+hQZxXluSlthRMzb1JLF1Wo+wYzwoLHmW1/ii0adl2WjXNrCSKrbEFoZ+iDJJ5U6sS9QbjQ7ShFzZvPge50ql2o/yz4iQ3ymio 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 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 > Signed-off-by: Lorenzo Stoakes > --- > 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