Re: AMD integrated graphics passthrough to KVM guest

[Gustav Sorenson <gu.sorenson@gmail.com>]

Hello,

> Ok, I have an X500 and I've never been able to get it to work correctly
> for passthrough.  It has additional quirks required beyond what either
> my HD5450 or HD7850 require.  Also, these old devices have a weird
> co-processor secondary function (see 01:00.1 in your lspci).  It
> probably needs to be co-assigned, but I'm not really sure what it does.
> FWIW, I don't think it's worth bothering to add support for anything
> older than a Radeon HD5xxx (I'd say HD6xxx, but I happen to have the
> HD5450 and it works, so...)

You're probably right that for old cards the demand isn't high enough
to justify the time spent. I don't plan to use the X1300 actively
anyway.

My plan was to initially buy the hardware as I have now, get VGA
passthrough of the integrated GPU to work, and then add another more
powerful (HD6xxx most probably) PCIe device, so that I could have a
headless host and two 3D-accelerated VMs.
Now that this seemingly won't work, I'd be happy if at least I could
run the IGP on the host and pass the not-yet-bought dedicated GPU to a
guest.
So, in order to not again discover that my plans won't work out after
I already bought the hardware, could you please tell me whether you
have any problems with your graphics cards in guests? Xen users seem
to suffer degraded performance after their guest systems shut
down/reboot. Is this the case with KVM and VFIO as well? Any other
issues, or models I should/should not buy?
Of course I've done some research on my own, but the VGA
virtualization topic seems to be quite volatile right now, and I find
contradicting information.

> One reason you're probably not getting any output is because the device
> doesn't have a ROM (ie. there's no video BIOS to run to get seabios to
> POST the device).  You'll either need to find a VBIOS for the device or
> use it as a secondary graphics device in the guest.  In some cases you
> can rip this out of the system ROM or ACPI tables.
>
> I don't think that using the vfio-vga-reset branches is helping you
> since it's a root complex device and we can't do a reset even if we knew
> how and if you use it as a secondary device, you might not even need the
> x-vga=on option for VFIO (ie. VFIO would handle this just like any
> regular PCI device).  Thanks,

Are you implying that I should be able to use the integrated GPU (if
it's not the primary, I suppose) as a secondary for a guest? If so, do
you expect 3D acceleration to work?

Thank you very much for your help, it's highly appreciated.