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

[Bronek Kozicki]

On Fri, 24 May 2019, at 7:17 PM, Micah Morton wrote:
> I’ve been working with an Intel Chrome OS device to see if integrated
> GPU passthrough works. The device is a 7th Generation (Kaby Lake)
> Intel Core i5-7Y57 with HD Graphics 615. So no discrete GPU. I think
> iGPU passthrough should work on this device.
> 
> Initializing the graphics hardware has proven to be the trickiest part
> in all of this, and I have a question I thought someone on this list
> might be able to answer:
> 
> Why does vfio enforce that I _need_ a VGA rom to be available in order
> to boot the guest in legacy passthrough mode
> (https://github.com/qemu/qemu/blob/master/hw/vfio/pci-quirks.c#L1616)?
> The Intel device I’m working with normally doesn’t initialize the GPU
> at all until the kernel is running, at which point the i915 driver
> does the initialization. So there is never actually any VGA rom
> anywhere on the system at any time for me to grab. I suppose I maybe
> could get one for this hardware from Intel or the web somewhere, but
> seems like if the device can normally initialize the GPU hardware from
> the kernel driver then it wouldn’t be too unreasonable to pass through
> the GPU and let the guest (with the same i915 driver) initialize the
> GPU without using a VGA rom. Do you think it would be reasonable for
> me to find a way to patch qemu/vfio/SeaBIOS to allow for this
> scenario?
> 
> I’ve tried commenting out some blocks in this function
> (https://github.com/qemu/qemu/blob/master/hw/vfio/pci-quirks.c#L1557)
> and patching SeaBIOS to avoid doing any kind of graphics init stuff in
> the guest, and am still working through the debugging, but was
> wondering if this is a reasonable approach? Or something that has been
> done before?
> 
> Thanks,
> Micah
> 
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>

I don't know about iGPU but for nVidia Quadro cards which I am passing through, I do not have a Rom. I use "<rom bar='off'/>" element in the device definition, and it just works, with an obvious limitation that guest doesn't show any image onscreen until the system is fully started. Perhaps it also helps that all my virtual machines are UEFI, not sure.


B.


-- 
  Bronek Kozicki
  brok at incorrekt.com