Re: [Xen-devel] Nvidia GPU passthrough and Device IDs

[Gordan Bobic <gordan@xxxxxxxxxx>]

On Thu, 28 Nov 2013 11:27:09 +0000, Andrew Cooper 
<andrew.cooper3@xxxxxxxxxx> wrote:
> On 28/11/13 11:21, Gordan Bobic wrote:
> > This has recently come to my attention:
> >
> > http://www.nvidia.com/object/user-selectable-machines.html
> >
> > along with this snippet of information:
> >
> > - Physical Function PCIid: 10ed:11bf - GK104GL [GRID K2]
> > - Virtual Function selectable from
> > PCIid: 10ed:118b - GK104 [GeForce K2 USM]
> > PCIid: 10ed:118c - GK104 [NVS K2 USM]
> > PCIid: 10ed: 11b0 - GK104GL [Quadro K2 USM]
> > PCIid: 10ed:11b1 - GK104GL [Tesla K2 USM]
> >
> > The way this reads to me is that it means that a different
> > device ID is exposed to domU than what runs on the host.
> >
> > Therefore, it must be possible to change the device ID
> > visible to domU to something other than what is visible
> > on the host.
> >
> > So, as per a question that has recently been asked, is
> > there a way to apply a software shim to expose a different
> > device ID to the domU when doing PCI passthrough? This
> > might completely avoid the need to modify the GeForce
> > cards in ways discussed here recently to make them
> > work in PCI passthrough mode by simply faking the
> > device ID exposed.
> >
> > Gordan
> All config space accesses get vetted by Qemu or pcifront.
>
> We have had one bug for a particular graphics card with PCI 
> passthrough
> which was fixed by faking up the wrong class code.  (There was a 
> windows
> XPDM/WDDM stack issue with the affected card, and the cirrus emulated
> graphics card was detected as "better" than the passed-through one)
I'll take that to be a resounding "yes" in answer to my
question. :)

Could you please point me in the rough direction of the code
and process flow that handles this?

Gordan

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