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

[Paige Thompson]

Hey, 

>From what I understand in general connecting devices straight to the root complex is problematic and they should be connected to a bridge. I was kind of wondering if anybody had any knowledge of this. I find the configuration really confusing. I still cant really tell how the topology works. 

Paige

Sent from my iPhone

> On Dec 25, 2018, at 5:06 AM, Bronek Kozicki <brok at spamcop.net> wrote:
> 
>> 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
> 
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