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Re: [Xen-devel] Fwd: Re: Xen 4.3 / 4.4 - concurrent APIs, VGA Passthru

On 07/28/2014 03:10 PM, Georg Bege wrote:

Thanks for your response, I can imagine hundred of people asked the same
questions already -
but as said it was hard to get an up to date documentation about this.
However I did experiment more with it, my graphics card is an GeForce
I came to the conclusion that passthru works great with XP (both 32bit
and 64bit) but giving me issue's whenever Im trying on Windows 7 64bit.

Unless something major has changed very recently, an unmodified GTX470 won't work passed through to a domU using unmodified drivers.

I am using Xen 4.3.0, and am using a pair of 780Ti cards at the moment, but this is a relatively recent upgrade from 470/480 cards.

GTX470 can be modified into a Quadro 5000 using a small BIOS change (google it, I'm sure you'll find information about it), after which it will work just fine passed through to a domU.

Having said that - it has recently been reported that various QEMU patches have neutered various ways the Nvidia driver uses to check whether it is running in a VM. Including things as lame as looking for QEMU's CPU model name/number override. Unsurprisingly, once you prevent the driver from detecting it is running in a VM, the card works fine.

One thing you might want to try is an older Nvidia driver. There has been a lot of cat-and-mouse game going on with QEMU getting patched to neuter checks for whether the stack is running virtualized, and Nvidia introducing new checks for it to attempt to continue making the GeForce cards not work virtualized.

But if you are not afraid of flipping a few bits on your GTX470 to turn it into a Quadro 5000, that is probably the easiest option that debugging the issue. IIRC was using my modified GTX470 and 480 cards with 320.xx and 331.xx drivers without problems.

It seems that vga passthru doesnt work for the newer qemu-xen model
(using Qemu 2.0.0), so Im using
qemu-xen-traditional along with the old bundled qemu-dm which works fine
for XP.

I am using qemu traditional on my system. I have two VMs running all the time, one running XP64, the other running 64-bit Windows. I have observed no issues at all with either guest OS.

So any idea why this is not working right for Win7?
Win7 also seems to be a lot slower with qemu-xen-traditional, is that a
bug in the old model?

It could be something in Xen 4.4. I am using 4.3 with no problems in a similar setup. The machine runs 24/7 and the VMs are always running as they are different "workstations". Everything works exactly as expected, including VM rebooting, and performance is close enough to native to not impede gaming (Crysis 3 at 2560x1600, Borderlands 2 at 3840x2400).


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