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charset="UTF-8" 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 7, 2020 at 4:25 PM Jason Gunthorpe wrote: > > 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() That's not quite right, An inode does come from the filesystem I just arranged for that inode's i_mapping to be set to a common instance. > Seems OK to use this more widely, but it feels a bit weird to live in > char/memory.c. Sure, now that more users have arrived it should move somewhere common. > 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 It still requires every file that can map physical memory to have its ->open fop do inode->i_mapping = devmem_inode->i_mapping; filp->f_mapping = inode->i_mapping; I don't see how you can centralize that part.