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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id 128sm13451661qki.26.2021.01.19.10.30.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Jan 2021 10:30:14 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1l1vld-003pg1-Ed; Tue, 19 Jan 2021 14:30:13 -0400 Date: Tue, 19 Jan 2021 14:30:13 -0400 From: Jason Gunthorpe To: Pavel Tatashin Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, vbabka@suse.cz, mhocko@suse.com, david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com, sashal@kernel.org, tyhicks@linux.microsoft.com, iamjoonsoo.kim@lge.com, mike.kravetz@oracle.com, rostedt@goodmis.org, mingo@redhat.com, peterz@infradead.org, mgorman@suse.de, willy@infradead.org, rientjes@google.com, jhubbard@nvidia.com, linux-doc@vger.kernel.org, ira.weiny@intel.com, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v5 08/14] mm/gup: do not allow zero page for pinned pages Message-ID: <20210119183013.GB4605@ziepe.ca> References: <20210119043920.155044-1-pasha.tatashin@soleen.com> <20210119043920.155044-9-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210119043920.155044-9-pasha.tatashin@soleen.com> 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 Mon, Jan 18, 2021 at 11:39:14PM -0500, Pavel Tatashin wrote: > Zero page should not be used for long term pinned pages. Once pages > are pinned their physical addresses cannot changed until they are unpinned. > > Guarantee to always return real pages when they are pinned by adding > FOLL_WRITE. > > Signed-off-by: Pavel Tatashin > --- > mm/gup.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) No, this will definitely break things Why does the zero page have to be movable? Jason