I've continued experimenting with GTX 980 passthrough with Arch Linux. I
noticed that the xf86-video-nouveau does NOT in fact have Maxwell support. One
would think otherwise looking at their Feature Matrix here:
https://nouveau.freedesktop.org/wiki/FeatureMatrix/
NV110 is the Maxwell family (GTX 980 including). But the mode-setting driver
can be used instead, so *I finally got GTX 980 PT working in Arch Linux*:
Add this file to /etc/X11/xorg.conf.d/20-nouveau.conf
```
Section "Device"
Identifier "NVidia Card"
Driver "modesetting"
BusID "PCI:0:5:0"
EndSection
```
Note that the PCI address is the address that the GPU has inside the VM (use
lspci IN the vm to find out that). Also "pci_msitranslate=0" has to be set in
VM configuration, otherwise VM will hang when X is started.
This is tested with Arch linux (up to date 8.7.2016), with Linux 4.6.3-1-ARCH,
modesetting and X versions 1.18.3.
-----
Ok, now that it's proven that newer Nvidia cards CAN in fact be passed through
in Xen, I tried the official NVidia binary driver, but it failed with error
message "The NVIDIA GPU at PCI:0:5:0 is not supported by the 367.27 NVIDIA
driver".
I think that's the proprietary driver refusing to work when it detects that
it's running under hypervisor (the Code 43 issue in Windows). Since KVM has for
a while supported hiding both the "KVMKVMKVMKVM" signature (with "-cpu kvm=off"
flag) as well as the Viridian hypervisor signature ("-cpu hv_vendor_id="..."
flag), and currently there's no such functionality in Xen, I patched it in
quite similar way to what Alex Willimson did to KVM.
Attached is a patch for Xen 4.6.1 that spoofs Xen signature ("XenVMMXenVMM" to
"ZenZenZenZen") and Viridian signature ("Microsoft Hv" to "Wetware Labs") when
"spoof_xen=1" and "spoof_viridian=1" are added VM configuration file.
The signatures are currently hard-coded, and currently there's no way to modify
them (beyond re-compiling Xen), since HVMLoader also uses a hard-coded string
to detect Xen and there's no API (understandably) to change that signature in
real-time.
WARNING! In case you try the patch, you MUST re-compile and install also
core-libvirt (in addition to vmm-xen) packages. Otherwise starting all DomUs
will fail! You have been warned :)
-----------------
With this patch, the *NVidia binary driver (version 367.27) works also on Arch
Linux* :)
However this was not enough on Windows 7 and 8.1 VMs (driver version 368.39)
still announce Error 43 :(
I would love if others could test this as well. Maybe the Windows driver uses
some other functionality to check for hypervisor, or maybe it's not a spoofing
issue at all.
More investigation coming in..
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