[vfio-users] vfio-pci passthrough issue after resume from suspend

[Max Ehrlich]

Hi,

I'm running into a weird issue with the vfio-pci driver

I use it on a laptop and I passthrough an external GPU connected via PCI
express. In general this works well, however if the laptop has *ever*
suspended since its last boot, then the windows guest reports an error 43
on the card and I get no output on the monitor that it is connected to.
This is really weird to me since it works fine if I boot the latop from
power-off, and hotplug the card. It's only if the laptop has ever suspended
since it's last boot that I see this issue. Even if it was suspended before
the card was ever hotplugged.

In other words:
laptop off -> boot -> hotplug GPU : works great
laptop off -> boot -> do stuff (GPU *NOT* connected) -> sleep -> resume ->
hotplug GPU: problem
laptop off -> boot -> hotplug GPU -> unplug GPU -> hotplug GPU : works great
laptop off -> boot -> hotplug GPU -> unplug GPU -> sleep -> resume ->
hotplug GPU: problem

Weird stuff...

I'm honestly not sure that vfio-pci is to blame here since there are so
many moving parts, but any guidance would be appreciated.

What I have tried is using the sysfs interface to
remove/rescan/poweroff/etc the PCI devices in questions (graphics card and
it's HDMI audio) and this also does help.

thanks,
Max
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