Re: Nvidia GPU passthrough and Device IDs

[Gordan Bobic <gordan@bobich.net>]

 On Thu, 28 Nov 2013 11:27:09 +0000, Andrew Cooper 
 <andrew.cooper3@citrix.com> 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