[vfio-users] Checking for EFI and general questions

[Marcel Bieberbach]

2015-11-24 18:18 GMT+01:00 Jens Zimmermann <zimmermannjens888 at gmail.com>:

>
> I am not sure I understand this correctly. Does this mean QEMU assigns a
> UEFI ROM of another 750 Ti on my card when it launches the VM?
>

Yes, it's just like flashing but without the need to flash your hardware.
The libvirt-XML line within the <hostdev> part would be:
<rom file='path-to-your.rom'/>
Techpowerup has a lot of bios versions of GPUs [1], and for your card there
seem to be two versions which, according to AW's script both have a valid
UEFI [2].


> If so, can it cause any problems because it's not the original ROM or
> because of the implementation in QEMU?
>

The unlikely danger of breaking the GPU's BIOS in the process of flashing
does of course not exist with the romfile-method. But all other dangers of
flashing the "wrong" bios do remain, like dangerous voltages, wrong fan
speeds that result in overheating etc. But: even among different
manufacturers with the same GPU model, this danger is quite low if you
watch for the clock and memory frequencies. With your model there should to
be even less to worry, as there are bios versions for your exact card. With
my older AMD card I blindly tested different BIOS versions of other
manufacturers till I found one that was stable. No permanent damages
occured, just temporary instabilities.

> You can also add an emulated GPU and install the guest drivers which
>> eliminate the need of GOP, you'll just have to boot the guest without video
>> output until the driver loads.
>>
> Is that the same as the romfile method?
>

No, you simply boot your virtual UEFI system without a compatible UEFI
card, so there's no output from it. As soon as Windows and the GPU drivers
are loaded, it doesn't matter, you just have no boot information (and miss
blue screens or problems when you try to upgrade Windows - then you just
have to replace the GPU with an emulated one for the length of this
procedure)


I'm one of the 750Ti-owners that have a working configuration. My
KFA²-model luckily came with an UEFI rom, but I believe with the available
roms on techpowerup you should get it running quite well, too. I'd
recommend using qemu-git and linux-vfio-lts from the Arch AUR (commenting
the patches you don't need) because this mostly "just works" and comes with
current versions needed to cheat the nvidia driver running on a performant
virtual machine.


[1] https://www.techpowerup.com/vgabios/index.php
[2]
https://www.techpowerup.com/vgabios/index.php?architecture=NVIDIA&manufacturer=Palit&model=GTX+750+Ti&interface=&memType=&memSize=
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