[vfio-users] Checking for EFI and general questions

[Jens Zimmermann]

>
> First off basically you want your GPUs directly connected to the CPU for
> best performance and not over the chipset which only has the equivalent of
> 4 PCIe-Lanes shared for everything you usually connect things to (USB,
> Sound, PCI, small PCIex1s). Secondly most Xeon E3/Core i have integrated
> graphics which are a) more powerful than a Geforce 210 and b) sport really
> good (libre) graphics drivers.
> Adding to the first point the difference between Intels small sockets
> (11xx) and big sockets (2011) ist the number of available PCIe-Lanes.
> The first only has 16 PCIe-Lanes from the CPU which are split in up to 3
> slots (and this only with higher end boards) and all other periphery/the
> chipset uses DMI for CPU-connection (4 PCIe-Lanes equivalent). PCIe-ACS ist
> not supported on the CPU port, where you put your GPU and the chipset is
> basically a field of quirks and luck I think (as an enduser) [and since you
> only have 4PCIe-Lanes (16GBit/s if I remember correctly) for all your
> periphery you don't really want to put your GPU there].
> The second has 28 to 40 Lanes from the CPU which are supported with ACS,
> so that the different physical slots get into separate IOMMU-groups and you
> can arbitrarily choose which addin-card you want to passtrough to the VM.
> For the chipset (onboard Sound, USB, SATA) the same things hold true as for
> the small platform.
>

That makes perfect sense, thank you, Felix!


>
>> 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=


Wow, then the rom file option is what I am looking for. Actually I had seen
those BIOSes, but I thought they would not work because the site says "UEFI
Supported: No". I am really glad that I don't have to buy a new graphics
card. :-D
Thanks a lot for the advice and explanation, Marcel!


I think I know all I need to know now and I have a good feeling going into
this. Thank you again for your help and support everybody! I will probably
be back in a few weeks asking for more guidance. :-P

So long,

Jens
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