Re: Windows 8 VGA Passthrough

[Gordan Bobic <gordan@bobich.net>]

On 10/27/2013 04:21 PM, John Wargo wrote:
> On 10/27/2013 09:27 AM, John Wargo wrote:
>> On 10/27/2013 04:30 AM, Gordan Bobic wrote:
>>> On 10/26/2013 09:58 PM, John Wargo wrote:
>>>> Geniuses,
>>>>
>>>> I've been trying to get VGA pass-through working on Windows 8, however
>>>> I've been running into a few issues.
>>>> Currently I can get Windows 8 running flawlessly without VGA
>>>> pass-through, however I'm planning on using it for gaming, so this wont
>>>> work.
>>>>
>>>> When I start windows 8, I am able to get past the install portion of
>>>> the
>>>> DVD, however it hangs on "Getting devices ready.. (n%)".
>>>>
>>>> Hardware Information :
>>>> AMD Fx6300
>>>> ASUS M5a99x evo r2.0
>>>> 16GB RAM
>>>> 6670 Radeon HD - Dom0
>>>> 7850 Radeon HD - Win8
>>>
>>> I have recently (recently as in over the past 48 hours) re-tried to
>>> get ATI VGA passthrough working, and the results are... interesting.
>>>
>>> HD4850 dom0 + HD7450 domU worked fine - or as fine as ATI passthrough
>>> ever seems to work (slowdown + white lines when dragging windows
>>> after a domU reboot). I am using XP64 domU so I can't eject the GPU
>>> (it says it is being used). But shutting down the domU, doing echo 1
>>> > reset for the GPU from dom0 (I don't know how this is implemented
>>> and whether it does anything) and then starting it up again sometimes
>>> recovers it. GPU-Z runs and reports the GPU correctly.
>>>
>>> HD4850 dom0 + HD7970 domU results in the entire host locking up as
>>> soon as the driver is loaded in domU. My solution is to swap the dom0
>>> GPU for an 8800GT, and the problem now doesn't occur. If I had to
>>> guess, BIOS on the HD7970 does something bizzare, finds the HD4850 on
>>> the bus, tries to do something to it, and ends up crashing the host.
>>> This could also be exacerbated by the fact that I have to run with
>>> relaxed checking and no PCI ACS due to NF200 bridges on my
>>> motherboard. Even so, however, GPU-Z crashes the domU and it's GPU
>>> _hard_ (but not the host, thankfully). It crashes it so hard, that
>>> the only cure is to reboot the host. Reseting the GPU via /sys/
>>> doesn't seem to do anything to help.
>>>
>>> Are you using gfx_passthru=1 in your config? The way most people have
>>> this kind of thing working is with gfx_passthru=0, i.e. secondary
>>> passthru. Don't assign the PCI device in the config when installing.
>>> Once the domU install is complete, shut it down, and add the GPU you
>>> want to pass through. Then fire up domU in VNC, install the driver,
>>> and with a bit of luck it will come up with output on the external
>>> monitor.
>>>
>>> Also make sure that radeon or radeonfb kernel drivers DO NOT load
>>> before the device is assigned to xen-pciback. The exact way to ensure
>>> this will depend on what distro and dom0 kernel you are using.
>>>
>>> Gordan
>> Status update:
>>
>> The catalyst drivers appear to be working perfectly fine, device
>> manager shows no errors, and everything works great, except that when
>> I plug my monitor into the second card, I get "No Signal" on the
>> monitor, then it shuts off.
>>
>> I though that secondary passthrough meant that it would pass the
>> virtual adapter in as primary, but I could use my GPU that I passed
>> through, so where am I wrong, and how do I do that?
>>
>> -John
> I've been doing some research into my VGA passthrough, so I've gone
> through the various debugging steps, and the only thing that I've found
> out of place is with "xl dmesg" (attached).
>
> Where do I go from here?

Sounds like your IOMMU may be buggy. You may need to set permissive=1 on 
your xen-pciback module.

I cannot remember if xl uses the same configuration, but for xm you 
could try putting this in your /etc/xen/xend-config.sxp:
(pci-passthrough-strict-check no)
(pci-dev-assign-strict-check no)

Gordan