[vfio-users] VFIO + UEFI virt VS i915 arbiter patch and a few more questions

[Milos Kaurin]

Hello,

Firstly, a big thanks to everyone contributing to VFIO and other
virtualization technologies that are making my GPU pass-through dream
come true.

I currently have this:

CPU: Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz

==================================
-[0000:00]-+-00.0  Intel Corporation 4th Gen Core Processor DRAM Controller
           +-01.0-[01]--+-00.0  NVIDIA Corporation GK104 [GeForce GTX 770]
           |            \-00.1  NVIDIA Corporation GK104 HDMI Audio Controller
           +-02.0  Intel Corporation Xeon E3-1200 v3/4th Gen Core
Processor Integrated Graphics Controller
           +-03.0  Intel Corporation Xeon E3-1200 v3/4th Gen Core
Processor HD Audio Controller
           +-14.0  Intel Corporation 8 Series/C220 Series Chipset
Family USB xHCI
           +-16.0  Intel Corporation 8 Series/C220 Series Chipset
Family MEI Controller #1
           +-19.0  Intel Corporation Ethernet Connection I217-LM
           +-1b.0  Intel Corporation 8 Series/C220 Series Chipset High
Definition Audio Controller
           +-1c.0-[02]--
           +-1c.1-[03-04]----00.0-[04]--
           +-1f.0  Intel Corporation Q87 Express LPC Controller
           +-1f.2  Intel Corporation 8 Series/C220 Series Chipset
Family 6-port SATA Controller 1 [AHCI mode]
           \-1f.3  Intel Corporation 8 Series/C220 Series Chipset
Family SMBus Controller
====================================================================

To avoid pasting iommu groups, every device is now in its own separate
group due to ACS patch.

Running on FC23 with a custom Kernel:
Linux gammalinux 4.2.8-300.milos.fc23.x86_64 #1 SMP Sun Jan 3 23:38:23
GMT 2016 x86_64 x86_64 x86_64 GNU/Linux

Custom kernel:
I have applied the ACS patch because my CPU root bridge (IIRC) was
grouped with the NVIDIA GPU/audio. I have also applied the i915
arbiter patch.

My virt is UEFI based (virt-manager instructions from the blog),
Windows 10 Guest, no audio (yet)

>From what I understood from Alex's blog and some other material of his
I found online, if you want to use an integrated Intel GPU for the
host, you have to apply the arbiter patch to avoid display corruption
etc because i915 driver is a liar.

My first question is: Is this only true for BIOS-based guests or does
it also go for UEFI based guests?
I'm asking because even though I applied the i915 arbiter patch, I
disabled the entry in modprobe.d to test and see what will happen.
Nothing happens on guest/host (Ran 3dmark extreme benchmarks multiple
times now).

Second question:
I'm thinking of letting the guest have the "USB xHCI" controller(14.0
from the lspci above). Due to some warnings from Alex on ACS being
potentially dangerous, I wanted to ask you guys whether it's safe to
use vfio-pci on that device.

Please let me know if you need any more info.

Regards,
Milos