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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id 2sm121866qtt.24.2021.01.19.15.35.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Jan 2021 15:35:22 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1l20Wv-003v6u-K8; Tue, 19 Jan 2021 19:35:21 -0400 Date: Tue, 19 Jan 2021 19:35:21 -0400 From: Jason Gunthorpe To: Pavel Tatashin Cc: LKML , linux-mm , Andrew Morton , Vlastimil Babka , Michal Hocko , David Hildenbrand , Oscar Salvador , Dan Williams , Sasha Levin , Tyler Hicks , Joonsoo Kim , mike.kravetz@oracle.com, Steven Rostedt , Ingo Molnar , Peter Zijlstra , Mel Gorman , Matthew Wilcox , David Rientjes , John Hubbard , Linux Doc Mailing List , Ira Weiny , linux-kselftest@vger.kernel.org Subject: Re: [PATCH v5 08/14] mm/gup: do not allow zero page for pinned pages Message-ID: <20210119233521.GE4605@ziepe.ca> References: <20210119043920.155044-1-pasha.tatashin@soleen.com> <20210119043920.155044-9-pasha.tatashin@soleen.com> <20210119183013.GB4605@ziepe.ca> <20210119184751.GD4605@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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, Jan 19, 2021 at 03:14:04PM -0500, Pavel Tatashin wrote: > I was thinking about a use case where userland would pin an address > without FOLL_WRITE, because the PTE for that address is not going to > be writable, but some device via DMA will write to it. That would be a serious bug in the get_user_pages caller to write to a page without using FOLL_WRITE Jason