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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id b14sm1405612qkn.123.2020.10.21.08.13.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Oct 2020 08:13:53 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kVFoG-003XHy-SZ; Wed, 21 Oct 2020 12:13:52 -0300 Date: Wed, 21 Oct 2020 12:13:52 -0300 From: Jason Gunthorpe To: Daniel Vetter Cc: DRI Development , LKML , KVM list , Linux MM , Linux ARM , linux-samsung-soc , "open list:DMA BUFFER SHARING FRAMEWORK" , linux-s390 , Daniel Vetter , Kees Cook , Dan Williams , Andrew Morton , John Hubbard , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Jan Kara , Bjorn Helgaas , Linux PCI , Daniel Vetter Subject: Re: [PATCH v3 12/16] PCI: Obey iomem restrictions for procfs mmap Message-ID: <20201021151352.GL36674@ziepe.ca> References: <20201021085655.1192025-1-daniel.vetter@ffwll.ch> <20201021085655.1192025-13-daniel.vetter@ffwll.ch> <20201021125030.GK36674@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 21, 2020 at 04:42:11PM +0200, Daniel Vetter wrote: > Uh yes. In drivers/gpu this isn't a problem because we only install > ptes from the vm_ops->fault handler. So no races. And I don't think > you can fix this otherwise through holding locks: mmap_sem we can't > hold because before vma_link we don't even know which mm_struct is > involved, so can't solve the race. Plus this would be worse that > mm_take_all_locks used by mmu notifier. And the address_space > i_mmap_lock is also no good since it's not held during the ->mmap > callback, when we write the ptes. And the resource locks is even less > useful, since we're not going to hold that at vma_link() time for > sure. > > Hence delaying the pte writes after the vma_link, which means ->fault > time, looks like the only way to close this gap. > Trouble is I have no idea how to do this cleanly ... How about add a vm_ops callback 'install_pages'/'prefault_pages' ? Call it after vm_link() - basically just move the remap_pfn, under some other lock, into there. Jason