[vfio-users] vga pass-thru and different gfx cards.

[Alex Williamson]

On Thu, Sep 10, 2015 at 10:47 AM, Torbjorn Jansson <
torbjorn.jansson at mbox200.swipnet.se> wrote:

> Hello all.
>
> first of all a big thanks to alex willamsons and his blog series about
> getting a graphic card passed thru to a vm.
> without those i wouldn't have been able to get it to work (more or less)
>
> first some hw info about my linux box where i'm using vfio & kvm:
> asus p8Z77-v le with 16gb ram and at the moment i'm using a nvidia gt610
> card from asus but i have also tried a gtx570.
>
> i got it to work after a bit of reading alex blogs and a lot of testing.
> i use the built in intel gfx card for the host since that is no good for
> anything else and the gt610 is passed thru to a win7 vm.
>
> first problem i have is that vga pass-thru only works one time after a
> cold boot.
> if i try to restart the vm or just power it of and on again i get a hard
> lockup of the host.
> this is the most annoying problem.
>

It's not clear to me why there are numerous reports of reset problems on
nvidia.  AFAIK, there's no broken hardware for nvidia in this space like
there is for AMD.  So if you're having reset problems, maybe it's because
you're not binding both GPU and audio functions to vfio-pci and therefore
vfio-pci can't do a bus reset on VM reset.  Maybe your motherboard freaks
out on the bus reset.  Maybe it's a ROM issue like Blank suggests.


> the second problem is because the gt610 and gtx570 don't have any uefi
> bios i am forced to use plain vga pass-thru and i have to use the vgaarb
> patch to get it to work at all.
> the problem (well, not really a problem but more of an extra complication)
> with this is that i have to manually patch and compile a new kernel.
> it also disables vaapi/vdpau on the host and i use the hosts gfx card
> where having those still working would have been beneficial.
>
>
> my questions:
> i assume that it is the old vga pass thru and not uefi vbios (gop?) that
> contributes to the reboot problems, is that correct?
>

Hard to say, I don't know why you're having reset issues.


> at least with uefi i assume i would be able to get rid of the vgaarb patch
> fixing vaapi/vdpau support.
>

Yes.

if i bought another gfx card for vm pass-thru how would an uefi card
> improve things? (gt720 for example)
> and would for example one of the not so expensive quadro cards like k420
> fix a few more issues? like the nvidia driver check for visualization.
>
> i assume the k420 have the highest probability of just working and getting
> rid of the most issues, what is not clear is if k420 also have uefi support.
>

Unfortunately you don't get anywhere higher in the nvidia support matrix
with Quadro until you get to the K2000 series or better.  K4xx, K6xx, K1xxx
are no more supported in a VM than a GeForce.  In fact, the low-end Quadros
might be a danger zone, we don't have much exposure to them.


> one annoying thing is that my asus gt610 card is supposed to be upgradable
> to uefi via a download tool from asus, but this doesnt work.
> first issue i had was it only worked on asus mainboard, luckily my linux
> box had an asus mainboard so i had to temporarily put in a new disk and
> install windows to test the upgrade tool, but it still failed but now on
> the gfx card and just said contact support.


Hmm, none of the Asus GT 610 ROMs on techpowerup have UEFI support either
and it doesn't look promising from the other vendors.  I was going to
recommend the GT 635 as a cheap OEM card that has good UEFI support, but
they no longer seem to be available on ebay.  That's really lame that the
asus card requires an asus mb, but even more lame that it still doesn't
include UEFI.
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