Re: Windows 8 VGA Passthrough

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

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