[vfio-users] VM doesn't boot if I use GPU passthrough

[Nicolas Roy-Renaud]

Ok, try to remove your passthrough from your guest configuration (either 
using virsh of virt manager). That is : remove the actual gpu 
(PCI:1:0.0) but keep the associated sound card (PCI:1:0.1) in there so 
virsh knows it needs to bind with this VFIO group.
 From there, create a file (let's say ./GPU_DEVICE.xml) containing just 
the following :

     1.
        <hostdevmode='subsystem'type='pci'managed='yes'>
     2.
        <source>
     3.
        <addressdomain='0x0000'bus='0x01'slot='0x00'function='0x0'/>
     4.
        </source>
     5.
        <addresstype='pci'domain='0x0000'bus='0x00'slot='0x02'function='0x0'/>
     6.
        </hostdev>


You'll be able to use this file to tell libvirt to append your GPU to 
guest's config at runtime, which somehow gets around the invalid ROM 
issue. Just run something like this :

virsh start Win10Full && sleep 60 && virsh attach-device --live --file ./GPU_DEVICE.xml

If I guessed right, windows should detect a new GPU and get the drivers 
in place once virsh is done mounting it. If that does work, you'll gave 
to run this same command every time you start your VM too, or at least 
until that specific bug is fixed. Hopefully that should get you some 
results so you can work your way from there.

On 2016-01-28 17:03, Ryan Flagler wrote:
> I was going to recommend you use UEFI, which is why I was asking. I've 
> personally had better luck getting things to pass through properly.
>
> Is your VM down when you try to cat the rom? The GPU needs to be 
> unused by anything.
>
I had the exact same symptoms on my Asus Strix 970, looks like a 
recurring issue with Asus cards. This happenned both when trying to 
start a VM with a managed passthrough and when attempting to dump the 
ROM from sysfs. I figured it's probably an issue with vfio-pci itself, 
and I still haven't fixed it wet, but the solution I posted above is my 
current workaround.
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