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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 12:49 PM Daniel Vetter wrote: > > On Wed, Oct 7, 2020 at 9:33 PM 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. > > But then I need to find the right one, plus I also need to find the > right one for the procfs side. That gets messy, and I already have no > idea how to really test this. Shared address_space is the same trick > we're using in drm (where we have multiple things all pointing to the > same underlying resources, through different files), and it gets the > job done. So that's why I figured the shared address_space is the > cleaner solution since then unmap_mapping_range takes care of > iterating over all vma for us. I guess I could reimplement that logic > with our own locking and everything in revoke_devmem, but feels a bit > silly. But it would also solve the problem of having mutliple > different mknod of /dev/kmem with different address_space behind them. > Also because of how remap_pfn_range works, all these vma do use the > same pgoff already anyway. True, remap_pfn_range() makes sure that ->pgoff is an absolute physical address offset for all use cases. So you might be able to just point proc_bus_pci_open() at the shared devmem address space. For sysfs it's messier. I think you would need to somehow get the inode from kernfs_fop_open() to adjust its address space, but only if the bin_file will ultimately be used for PCI memory.