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

[Ferdinand Pöll]

Hi Patrick, 

Am Samstag, 4. November 2017, 12:58:17 CET schrieb 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?

This sounds like a common problem which occurs when you are using a GPU in a VM without Message-Signal-based-Interrupts. Please try this: 
* https://wiki.lime-technology.com/UnRAID_Manual_6#Enable_MSI_for_Interrupts_to_Fix_HDMI_Audio_Support
* https://forums.guru3d.com/threads/windows-line-based-vs-message-signaled-based-interrupts.378044/

Hope this helps

Ferdinand