From: Dan Williams <email@example.com> To: Daniel Vetter <firstname.lastname@example.org> Cc: linux-s390 <email@example.com>, linux-samsung-soc <firstname.lastname@example.org>, "Jan Kara" <email@example.com>, "Kees Cook" <firstname.lastname@example.org>, "KVM list" <email@example.com>, "Jason Gunthorpe" <firstname.lastname@example.org>, "John Hubbard" <email@example.com>, LKML <firstname.lastname@example.org>, "DRI Development" <email@example.com>, "Linux MM" <firstname.lastname@example.org>, "Jérôme Glisse" <email@example.com>, "Linux PCI" <firstname.lastname@example.org>, "Bjorn Helgaas" <email@example.com>, "Daniel Vetter" <firstname.lastname@example.org>, "Andrew Morton" <email@example.com>, "Linux ARM" <firstname.lastname@example.org>, "Linuxemail@example.com" <firstname.lastname@example.org> Subject: Re: [PATCH 10/13] PCI: revoke mappings like devmem Date: Thu, 8 Oct 2020 01:35:41 -0700 [thread overview] Message-ID: <CAPcyv4gK82tpNWqwF-CFGPWU99WU-Sd84Y79zuQxMfZh1efoMQ@mail.gmail.com> (raw) In-Reply-To: <CAKMK7uHg48-fTR1L78p7q5vxD=Kgr_fBEj1pDLaYeuvTGSSFig@mail.gmail.com> On Thu, Oct 8, 2020 at 1:13 AM Daniel Vetter <email@example.com> wrote: > > On Thu, Oct 8, 2020 at 9:50 AM Dan Williams <firstname.lastname@example.org> wrote: > > > > On Wed, Oct 7, 2020 at 4:25 PM Jason Gunthorpe <email@example.com> 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 <firstname.lastname@example.org> 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. > > btw, why are you setting inode->i_mapping? The inode is already > published, changing that looks risky. And I don't think it's needed, > vma_link() only looks at filp->f_mapping, and in our drm_open() we > only set that one. I think you're right it is unnecessary for devmem, but I don't think it's dangerous to do it from the very first open before anything is using the address space. It's copy-paste from what all the other "shared address space" implementers do. For example, block-devices in bd_acquire(). However, the rationale for block_devices to do it is so that page cache pages can be associated with the address space in the absence of an f_mapping. Without filesystem page writeback to coordinate I don't see any devmem code paths that would operate on the inode->i_mapping. _______________________________________________ dri-devel mailing list email@example.com https://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2020-10-08 8:35 UTC|newest] Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-07 16:44 [PATCH 00/13] follow_pfn and other iomap races Daniel Vetter 2020-10-07 16:44 ` [PATCH 01/13] drm/exynos: Stop using frame_vector helpers Daniel Vetter 2020-10-07 20:32 ` John Hubbard 2020-10-07 21:32 ` Daniel Vetter 2020-10-07 21:36 ` John Hubbard 2020-10-07 21:50 ` Daniel Vetter 2020-10-07 16:44 ` [PATCH 02/13] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter 2020-10-07 20:43 ` John Hubbard 2020-10-07 16:44 ` [PATCH 03/13] misc/habana: Stop using frame_vector helpers Daniel Vetter 2020-10-07 20:38 ` John Hubbard 2020-10-07 16:44 ` [PATCH 04/13] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter 2020-10-07 20:46 ` John Hubbard 2020-10-07 16:44 ` [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter 2020-10-07 16:53 ` Jason Gunthorpe 2020-10-07 17:12 ` Daniel Vetter 2020-10-07 17:33 ` Jason Gunthorpe 2020-10-07 21:13 ` John Hubbard 2020-10-07 21:30 ` Daniel Vetter 2020-10-07 16:44 ` [PATCH 06/13] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter 2020-10-07 22:18 ` John Hubbard 2020-10-07 16:44 ` [PATCH 07/13] mm: close race in generic_access_phys Daniel Vetter 2020-10-07 17:27 ` Jason Gunthorpe 2020-10-07 18:01 ` Daniel Vetter 2020-10-07 23:21 ` Jason Gunthorpe 2020-10-08 0:44 ` John Hubbard 2020-10-08 7:23 ` Daniel Vetter 2020-10-07 16:44 ` [PATCH 08/13] s390/pci: Remove races against pte updates Daniel Vetter 2020-10-08 16:44 ` Gerald Schaefer 2020-10-08 17:16 ` Daniel Vetter 2020-10-07 16:44 ` [PATCH 09/13] PCI: obey iomem restrictions for procfs mmap Daniel Vetter 2020-10-07 18:46 ` Bjorn Helgaas 2020-10-07 16:44 ` [PATCH 10/13] PCI: revoke mappings like devmem Daniel Vetter 2020-10-07 18:41 ` Bjorn Helgaas 2020-10-07 19:24 ` Daniel Vetter 2020-10-07 19:33 ` Dan Williams 2020-10-07 19:47 ` Daniel Vetter 2020-10-07 22:23 ` Dan Williams 2020-10-07 22:29 ` Dan Williams 2020-10-08 8:09 ` Daniel Vetter 2020-10-07 23:24 ` Jason Gunthorpe 2020-10-08 7:31 ` Daniel Vetter 2020-10-08 7:49 ` Dan Williams 2020-10-08 8:13 ` Daniel Vetter 2020-10-08 8:35 ` Dan Williams [this message] 2020-10-08 12:41 ` Jason Gunthorpe 2020-10-07 16:44 ` [PATCH 11/13] mm: add unsafe_follow_pfn Daniel Vetter 2020-10-07 17:36 ` Jason Gunthorpe 2020-10-07 18:10 ` Daniel Vetter 2020-10-07 19:00 ` Jason Gunthorpe 2020-10-07 19:38 ` Daniel Vetter 2020-10-07 16:44 ` [PATCH 12/13] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter 2020-10-07 16:44 ` [PATCH 13/13] vfio/type1: Mark follow_pfn " Daniel Vetter 2020-10-07 17:39 ` Jason Gunthorpe 2020-10-07 18:14 ` Daniel Vetter 2020-10-07 18:47 ` Jason Gunthorpe
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