Re: [bugzilla-daemon@kernel.org: [Bug 219619] New: vfio-pci: screen graphics artifacts after 6.12 kernel upgrade]

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Jan 02, 2025 at 11:38:32AM -0700, Alex Williamson wrote:
> On Thu, 2 Jan 2025 10:04:02 -0700
> Alex Williamson <alex.williamson@redhat.com> wrote:
> 
> > On Thu, 2 Jan 2025 11:39:23 -0500
> > Peter Xu <peterx@redhat.com> wrote:
> > > OTOH, a pure question here is whether we should check pfn+pgoff instead of
> > > pgoff alone.  I have no idea how firmware would allocate BAR resources,
> > > especially on start address alignments.  I assume that needs to be somehow
> > > relevant to the max size of the bar, probably the start address should
> > > always be aligned to that max bar size?  If so, there should have no
> > > functional difference checking either pfn+pgoff or pgoff.  It could be a
> > > matter of readability in that case, saying that the limitation is about pfn
> > > (of pgtable) rather than directly relevant to the offset of the bar.  
> > 
> > Yes, I'm working on the proper patch now that we have a root cause and
> > I'm changing this to test alignment of pfn+pgoff.  The PCI BARs
> > themselves are required to have natural alignment, but the vma mapping
> > the BAR could be at an offset from the base of the BAR, which is
> > accounted for in our local vma_to_pfn() function.  So I agree that
> > pfn+pgoff is the more complete fix, which I'll post soon, and hope that
> > Precific can re-verify the fix.  Thanks,
> 
> The proposed fix is now posted here:
> 
> https://lore.kernel.org/all/20250102183416.1841878-1-alex.williamson@redhat.com
> 
> Please reply there with Tested-by and Reviewed-by as available.  Thanks,

#regzbot fix: 09dfc8a5f2ce ("vfio/pci: Fallback huge faults for unaligned pfn")

09dfc8a5f2ce appeared in v6.13-rc7.