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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id v30sm1069485qtj.52.2020.10.05.16.41.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Oct 2020 16:41:05 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kPa6K-000DCJ-94; Mon, 05 Oct 2020 20:41:04 -0300 Date: Mon, 5 Oct 2020 20:41:04 -0300 From: Jason Gunthorpe To: Daniel Vetter Cc: DRI Development , LKML , Daniel Vetter , Andrew Morton , John Hubbard , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Jan Kara , Dan Williams , Linux MM , Linux ARM , Pawel Osciak , Marek Szyprowski , Kyungmin Park , Tomasz Figa , 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: <20201005234104.GD5177@ziepe.ca> References: <20201002233118.GM9916@ziepe.ca> <20201004125059.GP9916@ziepe.ca> <20201005172854.GA5177@ziepe.ca> <20201005183704.GC5177@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, Oct 06, 2020 at 12:43:31AM +0200, Daniel Vetter wrote: > > iow I think I can outright delete the frame vector stuff. > > Ok this doesn't work, because dma_mmap always uses a remap_pfn_range, > which is a VM_IO | VM_PFNMAP vma and so even if it's cma backed and > not a carveout, we can't get the pages. If CMA memory has struct pages it probably should be mmap'd with different flags, and the lifecycle of the CMA memory needs to respect the struct page refcount? > Plus trying to move the cma pages out of cma for FOLL_LONGTERM would > be kinda bad when they've been allocated as a contig block by > dma_alloc_coherent :-) Isn't holding a long term reference to a CMA page one of those really scary use-after-free security issues I've been talking about? I know nothing about CMA, so can't say too much, sorry Jason