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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id d14sm1449111qtr.62.2020.10.07.06.06.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Oct 2020 06:06:10 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kQ990-000tst-7Q; Wed, 07 Oct 2020 10:06:10 -0300 Date: Wed, 7 Oct 2020 10:06:10 -0300 From: Jason Gunthorpe To: Daniel Vetter Cc: Tomasz Figa , Marek Szyprowski , DRI Development , LKML , Daniel Vetter , Andrew Morton , John Hubbard , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Jan Kara , Dan Williams , Linux MM , Linux ARM , Pawel Osciak , Kyungmin Park , Inki Dae , Joonyoung Shim , Seung-Woo Kim , linux-samsung-soc , "open list:DMA BUFFER SHARING FRAMEWORK" , Oded Gabbay Subject: Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Message-ID: <20201007130610.GP5177@ziepe.ca> References: <20201002233118.GM9916@ziepe.ca> <725819e9-4f07-3f04-08f8-b6180406b339@samsung.com> <20201007124409.GN5177@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 Wed, Oct 07, 2020 at 02:58:33PM +0200, Daniel Vetter wrote: > On Wed, Oct 7, 2020 at 2:48 PM Tomasz Figa wrote: > > > > On Wed, Oct 7, 2020 at 2:44 PM Jason Gunthorpe wrote: > > > > > > On Wed, Oct 07, 2020 at 02:33:56PM +0200, Marek Szyprowski wrote: > > > > Well, it was in vb2_get_vma() function, but now I see that it has been > > > > lost in fb639eb39154 and 6690c8c78c74 some time ago... > > > > > > There is no guarentee that holding a get on the file says anthing > > > about the VMA. This needed to check that the file was some special > > > kind of file that promised the VMA layout and file lifetime are > > > connected. > > > > > > Also, cloning a VMA outside the mm world is just really bad. That > > > would screw up many assumptions the drivers make. > > > > > > If it is all obsolete I say we hide it behind a default n config > > > symbol and taint the kernel if anything uses it. > > > > > > Add a big comment above the follow_pfn to warn others away from this > > > code. > > > > Sadly it's just verbally declared as deprecated and not formally noted > > anyway. There are a lot of userspace applications relying on user > > pointer support. > > userptr can stay, it's the userptr abuse for zerocpy buffer sharing > which doesn't work anymore. At least without major surgery (you'd need > an mmu notifier to zap mappings and recreate them, and that pretty > much breaks the v4l model of preallocating all buffers to make sure we > never underflow the buffer queue). And static mappings are not coming > back I think, we'll go ever more into the direction of dynamic > mappings and moving stuff around as needed. Right, and to be clear, the last time I saw a security flaw of this magnitude from a subsystem badly mis-designing itself, Linus's knee-jerk reaction was to propose to remove the whole subsystem. Please don't take status-quo as acceptable, V4L community has to work to resolve this, uABI breakage or not. The follow_pfn related code must be compiled out of normal distro kernel builds. Jason