[vfio-users] radeon vfio bus information issue?

[Alex Williamson]

On Mon, 24 Oct 2016 10:20:08 -0700
globalgorrilla at fastmail.fm wrote:

> Hi,
> 
> Pass-through works fine with the the same linux 4.8 VM and nouveau and a 
> Quadro K2200.
> 
> Passing-through both a R7 260X and and a R9 290 I get the same kernel 
> oops:
> 
> IP: [<ffffffffc029efd9>] drm_pcie_get_speed_cap_mask+0x39/0xf0 [drm]
> 
> More here:
> http://pastebin.com/Waysyk2e
> 
> Both the AMD cards work fine if I pass them through to a Windows VM.
> 
> I'm supposing this might likely be then an issue with Radeon.
> 
> However the oops makes me think perhaps it's breaking on unexpected PCIE 
> information?
> 
> Is it possible there some missing information in that radeon is looking 
> for that's missing? What PCIE information is passed through by vfio 
> (lspci from both host and vm also in the pastebin)?
> 
> Anybody using radeon with passthrough AMD cards and seen this?

Radeon with a Linux guest is actually one of the few cases where you
need to be running a Q35 machine with the GPU placed behind a PCIe
downstream/root port.  The code blindly assumes that an upstream PCIe
bridge is present and tries to poke registers on it.