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Re: [Xen-users] [Xen-devel] VGA passthough still not working

Hi John,

I am trying to pass my secondary graphics card through to the VM. My dom0 runs with the primary card (an onboard GPU).

What happens with me is that the secondary card (GTX480) is relinquished to pciback and according to the logs, it looks like the card is passed through successfully to the domU.
What happens though is a bit puzzling (with gfx_passthru=1):
1) When I start the domU, my dom0 screen goes blank (which is using a different graphics card than is assigned to the domU)
2) The domain does not boot; i.e. the CDROM does not spin up.
3) If I connect to the domain via vnc, I see only the qemu console.

With gfx_passthru=0, the following happens:
a) The domain boots fine (the CDROM spins up).
b) I can connect to the OS in the domain via vnc.
c) The Windows OS installs fine and functions fine afterwards too.
d) I can see the GFX480 card in the device manager, but I can not use the device (even if I install the correct drivers for it)

Check out the details of my problem here. I have marked the things that concern me in red. I am obviously missing something...



On Fri, Jan 20, 2012 at 8:46 PM, John Sherwood <jrs@xxxxxx> wrote:
Most people run Xen for headless virtual machines, and VGA passthrough requires VT-d support in both the CPU and motherboard.  VGA passthrough is also somewhat dependent on the card you're using it with, so it's a hard thing to test.  If you want it to get more love, then you're the best situated person to do it :)

However, on the topic of Sandi's issue:
If your monitor goes black, that's a GOOD sign - it's indicative that the dom0 is relinquishing control of the graphics card, so at least that's working.  In my experience using graphics passthrough, this problem is related to your card not being fully supported; essentially, Xen can't pass your card through to the VM during boot.  If you leave the `gfx_passthru` option *disabled*, you'll have the emulated cirrus card (by default) and it will at least boot successfully.  Here's some step by step suggestions/instructions:

  • disable gfx_passthru in config (delete the option or set it to 0)
  • enable VNC, listening on all interfaces
  • start the VM - your screen should still go black
  • From another machine (what with your screen being black), connect in via VNC and fire up the device manager in XP.  I don't have any XP boxes left, but in Windows 7, you should see a device in an error state under 'Display adapters'.
  • Check its PCI slot under 'details' - "Location Paths" should help.  Compare that to `xm pci-list [domain name]` to see if it matches up with the graphics card.
  • Install the driver for that device
  • Reboot.  You won't see the BIOS on the monitor, but it should use it once Windows takes over.

If something in there doesn't work, hopefully I can help you debug - I went through a lot of this a while back.

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