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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id r17sm2946100qtc.22.2020.10.07.16.24.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Oct 2020 16:24:49 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kQIng-001Ing-AW; Wed, 07 Oct 2020 20:24:48 -0300 Date: Wed, 7 Oct 2020 20:24:48 -0300 From: Jason Gunthorpe To: Dan Williams Cc: Daniel Vetter , DRI Development , LKML , KVM list , Linux MM , Linux ARM , linux-samsung-soc , "Linux-media@vger.kernel.org" , linux-s390 , Daniel Vetter , Kees Cook , Andrew Morton , John Hubbard , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Jan Kara , Bjorn Helgaas , linux-pci@vger.kernel.org Subject: Re: [PATCH 10/13] PCI: revoke mappings like devmem Message-ID: <20201007232448.GC5177@ziepe.ca> References: <20201007164426.1812530-1-daniel.vetter@ffwll.ch> <20201007164426.1812530-11-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 07, 2020 at 12:33:06PM -0700, Dan Williams wrote: > On Wed, Oct 7, 2020 at 11:11 AM Daniel Vetter wrote: > > > > Since 3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims > > the region") /dev/kmem zaps ptes when the kernel requests exclusive > > acccess to an iomem region. And with CONFIG_IO_STRICT_DEVMEM, this is > > the default for all driver uses. > > > > Except there's two more ways to access pci bars: sysfs and proc mmap > > support. Let's plug that hole. > > Ooh, yes, lets. > > > > > For revoke_devmem() to work we need to link our vma into the same > > address_space, with consistent vma->vm_pgoff. ->pgoff is already > > adjusted, because that's how (io_)remap_pfn_range works, but for the > > mapping we need to adjust vma->vm_file->f_mapping. Usually that's done > > at ->open time, but that's a bit tricky here with all the entry points > > and arch code. So instead create a fake file and adjust vma->vm_file. > > I don't think you want to share the devmem inode for this, this should > be based off the sysfs inode which I believe there is already only one > instance per resource. In contrast /dev/mem can have multiple inodes > because anyone can just mknod a new character device file, the same > problem does not exist for sysfs. The inode does not come from the filesystem char/mem.c creates a singular anon inode in devmem_init_inode() Seems OK to use this more widely, but it feels a bit weird to live in char/memory.c. This is what got me thinking maybe this needs to be a bit bigger generic infrastructure - eg enter this scheme from fops mmap and everything else is in mm/user_iomem.c Jason