Re: Windows 8 VGA Passthrough

[John Wargo <wargo.john25@gmail.com>]

On 10/27/2013 02:35 PM, Gordan Bobic wrote:
> 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
>
Gordan,

According to the xenbits page on xl.cfg, it appears the permissive will 
only work with PV guests, not HVM..

-John