[Xen-users] gtx 9xx passthrough

[Kuba <kuba.0000@xxxxx>]

Dear List,

I'm going to have to replace my old Quadro with a new GTX 9xx GPU. I've 
been using GPU passthrough on my workstation for quite some time, but 
now it seems I've run out of lack. I can't find any readily available 
way to pass through the latest GTX 9xx cards. Any idea would be much 
appreciated, but if there is none - maybe I should attempt to do one of 
the following?
Tweaking NVIDIA's Windows drivers is way beyond my skill set (and would 
probably violate the EULA). Hardmodding, if at all possible, is a last 
resort (btw, anyone heard of any successful attempt at hardmodding 
GTX980/980TI?). I have no problem with changing some resistors, but it 
would be probably impossible to completely cover your tracks and reverse 
the changes in an unnoticeable manner in case of RMA.
One last thing that comes to my mind is to hide Xen's CPUID vendor ID, 
just like QEMU+KVM do. Assuming that the drivers recognize Xen only by a 
simple string comparison with "XenVMMXenVMM", changing this string for a 
particular VM might do the trick.
Unfortunately, a quick search through Xen's sources shows that this 
string is hardcoded in many places - not only in the hypervisor itself, 
but also in QEMU, SeaBios, Windows PV Drivers...
If I understand this correctly, to mislead only the NVIDIA drivers, two 
things would have to be done:
 - the hypervisor should change the vendor ID string (or simply not 
change it at all) for a chosen VMs,
 - all the other software that detects Xen by vendor ID should be 
modified appropriately.
The most straightforward way that comes to my mind is to make Xen change 
the vendor ID to e.g. "HiddenXenVMM" for a chosen VM and everywhere else 
change the conditional statements from (pseudocode):
if (vendor_id == "XenVMMXenVMM")

to:

if (vendor_id == "XenVMMXenVMM" || vendor_id == "HiddenXenVMM")

I've only just took a glimpse at the source codes, so I'm not sure if I 
make any sense at all.
I'm willing to poke around a bit, but I would be very grateful if 
someone could point me in the right direction. Any guidance would be 
much appreciated.
Best regards,
Kuba

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