[vfio-users] Question about integrated GPU passthrough and initialization

[Alex Williamson]

On Tue, 28 May 2019 09:35:16 -0700
Micah Morton <mortonm at chromium.org> wrote:

> Ah ok thanks!
> 
> The qemu command line i was using is here: `qemu-system-x86_64
> -chardev stdio,id=seabios -device
> isa-debugcon,iobase=0x402,chardev=seabios -m 2G -smp 2 -M pc -vga none
> -usbdevice tablet -cpu host,-invpcid,-tsc-deadline,check -drive
> 'file=/path/to/image.bin,index=0,media=disk,cache=unsafe,format=raw'
> -enable-kvm -device
> vfio-pci,x-igd-opregion=on,host=00:02.0,id=hostdev0,bus=pci.0,addr=0x2,rombar=0
> -device 'virtio-net,netdev=eth0' -netdev
> 'user,id=eth0,net=10.0.2.0/27,hostfwd=tcp:127.0.0.1:9222-:22'`
> 
> It didn't work, but now at least I know why:
> [    0.316117] i915 0000:00:02.0: No more image in the PCI ROM
> [    0.316261] [drm] Failed to find VBIOS tables (VBT)
> 
> If I can expose the VBT to the VM maybe it will work :)

Hmm, looking at i915 it seems it didn't find this VBT thing in the
OpRegion so tried to look at the ROM, which comments indicate would
only be the VBT location on an older device.  QEMU should fail if
x-igd-opregion=on is specified but the host kernel didn't provide an
OpRegion at all, so we've at least done some minimal sanity checking at
the host kernel before exposing it, but maybe the OpRegion is missing
some things on this chrome device vs a standard pc?  Maybe Chrome OS
uses a modified i915 driver that doesn't depend on it so the firmware
guys stripped it?  You could write a minimal vfio driver to dump
the opregion data if you want to parse it by hand.  Thanks,

Alex