[vfio-users] Hotplug problem (Was: USB device passthrough regression?)

[Patrick O'Callaghan]

On Wed, 2017-11-01 at 11:03 +0000, Patrick O'Callaghan wrote:
> On Wed, 2017-11-01 at 10:01 +0100, P. Pronk wrote:
> > Ah, only just noticed its probably the same OEM card as Corey is using ;)
> > 
> > For full disclosure, this is the pci-e riser I am using:
> > https://www.ebay.com/itm/Mini-PCI-E-PCI-Express-Extension1X-Riser-Card-Power-USB-30cm-Extender-Cable-4pin/361629487578
> > 
> > I really dont recommend using those ribbon type risers for that. It
> > might fit and or work but with a double slot gpu you have to bent the
> > ribbon almost 180 degrees to pass under your gpu cooler which can cause
> > the ribbon to come of the board. And then you risk short circuiting if
> > the open ends of that ribbon touch.
> 
> Thanks, I don't think I need a riser, but I ordered this card, which
> several people claim works on Linux: https://www.amazon.co.uk/gp/produc
> t/B00B6ZCNGM/ref=od_aui_detailpages00?ie=UTF8&psc=1

I installed the above card and it's detected on Linux. Passing it
through to my Windows VM (as a PCI device) also works and I can get on
with scanning all those slides, so that's a win.

However I found that on playing a Windows game (Mass Effect 3) I would
get a hard system freeze in the middle of play. This actually brought
down my Linux system as well. Rebooting directly into Windows (no VM)
got the same freeze, so most likely it's a bug in the game (though why
that would affect the host is a mystery). Removing the PCI passthrough
fixed the problem, i.e. no further crashes.

I can live with restarting the VM between scanning and gaming, but a
more elegant solution would be to hotplug the PCI card in the VM.
Unplugging it works, but if I try to add it again I get a dialog box
saying it might take a while, after which the *entire system* freezes
and a hard reset of the host is the only resort.

Is there some special magic to make this work, or is this a known bug
in QEMU/KVM and I should just forget about it?

poc