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[86.156.84.164]) by smtp.gmail.com with ESMTPSA id v15-20020a05600c444f00b003f09cda253esm28758504wmn.34.2023.04.28.10.42.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Apr 2023 10:42:42 -0700 (PDT) Date: Fri, 28 Apr 2023 18:42:41 +0100 From: Lorenzo Stoakes To: Jason Gunthorpe Cc: David Hildenbrand , "Kirill A . Shutemov" , Peter Xu , 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 , John Hubbard , Jan Kara , Pavel Begunkov , Mika Penttila , David Howells , Christoph Hellwig Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: <34bc4f3c-8dfe-46ec-9f9b-358cdf4c37e3@lucifer.local> References: <62ec50da-5f73-559c-c4b3-bde4eb215e08@redhat.com> <6ddc7ac4-4091-632a-7b2c-df2005438ec4@redhat.com> <20230428160925.5medjfxkyvmzfyhq@box.shutemov.name> <39cc0f26-8fc2-79dd-2e84-62238d27fd98@redhat.com> <20230428162207.o3ejmcz7rzezpt6n@box.shutemov.name> <173337c0-14f4-3246-15ff-7fbf03861c94@redhat.com> <20230428165623.pqchgi5gtfhxd5b5@box.shutemov.name> <1039c830-acec-d99b-b315-c2a6e26c34ca@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On Fri, Apr 28, 2023 at 02:31:38PM -0300, Jason Gunthorpe wrote: > On Fri, Apr 28, 2023 at 07:02:22PM +0200, David Hildenbrand wrote: > > > > No. VMA cannot get away before PTEs are unmapped and TLB is flushed. And > > > TLB flushing is serialized against GUP_fast(). > > > > The whole CONFIG_MMU_GATHER_RCU_TABLE_FREE handling makes the situation more > > complicated. > > Yeah, you have to think of gup_fast as RCU with a hacky pre-RCU implementation > on most architectures. > > We could make page->mapping safe under RCU, for instance. > > Jason Does it really require a change though? I might be missing some details, but afaict with interrupts disabled we should be ok to deref page->mapping to check PageAnon and a_ops before handing back a page right?