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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id 8sm207979qkd.47.2020.09.17.09.39.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Sep 2020 09:39:08 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kIww7-000WtZ-PQ; Thu, 17 Sep 2020 13:39:07 -0300 Date: Thu, 17 Sep 2020 13:39:07 -0300 From: Jason Gunthorpe To: Christian =?utf-8?B?S8O2bmln?= Cc: Daniel Vetter , Linux Kernel Mailing List , dri-devel , "moderated list:DMA BUFFER SHARING FRAMEWORK" , Linux MM , Andrew Morton , "open list:DMA BUFFER SHARING FRAMEWORK" Subject: Re: [Linaro-mm-sig] Changing vma->vm_file in dma_buf_mmap() Message-ID: <20200917163907.GI8409@ziepe.ca> References: <20200917113110.GE8409@ziepe.ca> <6fd74b84-959c-8b3b-c27b-e9fbf66396c7@gmail.com> <20200917121858.GF8409@ziepe.ca> <20200917143551.GG8409@ziepe.ca> <5b330920-c789-fac7-e9b1-49f3bc1097a8@gmail.com> <20200917152456.GH8409@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable 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 Thu, Sep 17, 2020 at 06:06:14PM +0200, Christian K=C3=B6nig wrote: > > > If it is already taking a page fault I'm not sure the extra functio= n > > > call indirection is going to be a big deal. Having a uniform VMA > > > sounds saner than every driver custom rolling something. > > >=20 > > > When I unwound a similar mess in RDMA all the custom VMA stuff in t= he > > > drivers turned out to be generally buggy, at least. > > >=20 > > > Is vma->vm_file->private_data universally a dma_buf pointer at leas= t? > > Nope. I think if you want this without some large scale rewrite of a > > lot of code we'd need a vmops->get_dmabuf or similar. Not pretty, but > > would get the job done. >=20 > Yeah, agree that sounds like the simplest approach. I don't think that will fly, it is clearly only papering over a mess inside DRM/dma buf :\ Jason