Re: [Xen-devel] Windows 8 VGA Passthrough

[John Wargo <wargo.john25@xxxxxxxxx>]

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

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