[vfio-users] Installing Catalyst prevents VM from booting.

[Bronek Kozicki]

On Tue, 25 Dec 2018, at 12:57 PM, Paige Thompson wrote:
> Hi,
> 
> As you probably know there is a workaround to use i440fx instead of q35 
> to get the R9 390 working with VFIO. However, I have managed to get it 
> working with Q35 by adding a PCIe bridge as well as upstream and 
> downstream ports to the configuration. You've probably noticed that the 
> R9 390 card works fine with Q35 up until the point in which you install 
> the AMD drivers and then it starts crashing. As near as I can tell the 
> driver simply doesn't like it if you attach the video card directly to 
> the root complex.
> 
> Here is a link to the configuration that I am using: 
> https://gitlab.com/snippets/1788426#note_127191397
> qemu command-line rough translation: 
> https://gitlab.com/snippets/1788426#note_127194064
> For the entire work log :  https://gitlab.com/snippets/1788426
> 
> I'd also like to point out that this also works with a Linux guest as I 
> confirmed a moment ago. I never could get Linux to work with either 
> i440fx or q35 before I tried using a pcie bridge in q35. My 
> understanding of why Windows would work with i440fx is unclear but I 
> know that pcie devices essentially speak the same as pci devices and 
> there are no pcie devices on i440fx platforms; still whatever the amd 
> drivers check for is somehow circumvented in that particular 
> configuration.
> 
> I'm surprised nobody knew to suggest this, I sort of figured this out 
> based on something I read somewhere about how it's a bad idea to allow 
> devices to talk directly as discrete devices to the root complex anyway. 
> So, I gave this a try and low and behold it worked. It won't give you 
> any performance improvements, but q35 is a more accurate emulation of a 
> modern system and may help with other aspects of troubleshooting, it 
> just requires more topology complexity to be configured correctly.
> 
> Hope that helps,


HI Paige


thanks for sharing, this is interesting. FWIW I am currently using Ubuntu Bionic with vfio GPU passthrough but I have given up on AMD cards years ago and am using nVidia Quadro now, which does not have problems with 440FX.


B.

-- 
  Bronek Kozicki
  brok at spamcop.net