[vfio-users] i915 vgaarb patch not work as expect, always get "[drm:intel_uncore_check_errors [i915]] *ERROR* Unclaimed register before interrupt"

[Cong Zhang]

Hi all,

  I manual apply the i915 patch( https://lkml.org/lkml/2014/5/9/517) to
linux 4.1.6 debian kernel, but it does not work as expect!
  I can make vm with OVMF vga passthrough work proper, but for vm in legacy
bios mode with smbios, it always failed.

  I add some log to i915 module, and I am  sure  VGA memory was disable on
Intel HD as *i915_disable_vga_mem* was called*(is just call once ok?)*!

  1. when I do vga passthrough with out ovmf, i got some drm error from
dmesg
*[  907.640484] [drm:intel_uncore_check_errors [i915]] *ERROR* Unclaimed
register before interrupt *
  2. when i boot vm without -vga none from command line,
*  my host graphics are corrupted and if I switch to text console by
ctrl-alt-f1, and switch back with ctrl-alt-f7, it will recover.*
*  it's very similar like question 3 in
http://vfio.blogspot.com/2014/08/vfiovga-faq.html
<http://vfio.blogspot.com/2014/08/vfiovga-faq.html> , but I already apply
the patch with some part confuse as code struct was changed(I do
some adjust, to make it work, as the patch is straight forward, so it
should work as AW expect!?)*
   3. kvm crash some time with callstack in the attatch

*  S*ome ext information*:*
*  my host is **IGD**+Nvidia, and boot from uefi mode with no csm support,
 I need boot with intel_iommu=on,igfx_off to make IGD works*
*  Any help will be very appreciate.*

Thanks,
Cong
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