[fedora-virt] Issues with VGA passthrough using KVM and VFIO

[Alex Williamson]

On Thu, 2013-12-19 at 12:41 -0500, Stewart Adam wrote:
> On 2013-12-19 10:19 AM, Alex Williamson wrote:
> > On Thu, 2013-12-19 at 01:48 -0500, Stewart Adam wrote:
> >> Hi,
> >>
> >> I am trying to get VGA passthrough working using KVM and VFIO like
> >> described on this [1] thread and ran into some issues I was hoping
> >> someone could shed some light on. I have tried various configurations,
> >> but can't seem to get it working correctly. Either I get "Code 10"
> >> device error in Windows, or I get a BSOD 0x00000116 (VIDEO_TDR_ ERROR:
> >> attempt to reset the display driver and recover from a timeout failed)
> >> when booting the machine after installing the Catalyst 3D drivers.
> >> Other users on the Arch Linux forum have also reported similar issues.
> >>
> >> <cut>
> >
> > Hi Stewart,
> >
> > The "x" in the x-vga option is for eXperimental.  It works in some
> > cases, not others.  The archlinux forum thread is the best place to
> > either get help or commiserate with others having the same problem.  The
> > advice there is largely not distribution specific.  The 0x116 BSOD is a
> > common problem with assigned Radeon graphics, we don't have a solution
> > yet.  Also note that this work is still under development, for the
> > current "state of the art" you need a 3.13-rc kernel and qemu.git, and
> > you may need to patch in some Intel graphics fixes for VGA arbitration.
> > Even then, I have no reason to suspect the 0x116 BSOD is fixed.  More
> > users seem to be having success with Nvidia cards, so if that's an
> > option for you, it may be the quickest path to results.  Thanks,
> >
> > Alex
> 
> Hi Alex,
> 
> Thanks for replying so quickly. Ironically, I normally buy nVidia and 
> purchased this Radeon card because I had read online they tend to do 
> passthrough better (with Xen at least)... I didn't have much luck when I 
> tried a Xen VM either though. I do have an nVidia card handy and will try 
> that later tonight.
> 
> Would the VGA arbitration patches relate to the Code 10 errors? Also, I will 
> try again with 3.13-rc later this week but should I use qemu-vfio.git or 
> qemu.git?

Probably not related to the Code 10, but I'm no expert in Windows error
codes.

> I realize this is all bleeding edge and thank you for all of your work on 
> it. Is there anything I can do to help you debug the 0x116 problem?

vfio has plenty of debug support for tracing accesses to the card, it
simply needs to be turned on in the source file.  The issue is
identifying the problem among all the output.  With a closed source
guest and driver, and lack of hardware documentation, it's quite a lot
of guesswork.

> Lastly, out of curiosity - is the 0x116 error dependent on particular piece 
> of hardware or it's a problem with the emulation layer + certain GPUs?

No idea.  Thanks,

Alex