Re: IGD pass-through failures since 4.10.

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Feb 14, 2022 at 12:00:11AM -0600, Dr. Greg wrote:
> Good morning, I hope the week is starting well for everyone.
> 
> We've made extensive use of PCI based graphics pass through for many
> years, since around Xen 4.2.  In fact, we maintained a set of patches
> for ATI cards against qemu-traditional that have seen a lot of
> downloads from our FTP site.
> 
> We ended up switching to IGD based graphics a couple of years ago and
> built a stack on top of Xen 4.10 using qemu-traditional.  That
> coincided with our transition from Windows 7 to Windows 10.
> 
> We've never enjoyed anywhere near the stability with IGD/Windows-10
> that we had with the ATI/Windows-7 desktops, ie. we see fairly
> frequent crashes, lockups, reduced performance etc.  The ATI/Windows-y
> desktops were almost astonishingly reliable, ie. hundreds of
> consecutive Windows VM boot/passthrough cycles.
> 
> In order to try and address this issue we set out to upgrade our
> workstation infrastructure.  Unfortunately we haven't found anything
> that has worked post 4.10.
> 
> To be precise, 4.11 with qemu-traditional works, but upon exit from
> the virtual machine, to which the graphics adapter and USB controller
> are passed through to, both the USB controller and the graphics
> controller cannot be re-initialized and re-attached to the Dom0
> instance.
> 
> It appears to be a problem with mapping interrupts back to dom0 given
> that we see the following:
> 
> Feb 10 08:16:05 hostname kernel: xhci_hcd 0000:00:14.0: xen map irq failed 
> -19 for 32752 domain
> 
> Feb 10 08:16:05 hostname kernel: i915 0000:00:02.0: xen map irq failed -19 
> for 32752 domain
> 
> Feb 10 08:16:12 hostname kernel: xhci_hcd 0000:00:14.0: Error while assigning 
> device slot ID

Are you testing with an hypervisor with debug enabled? If not, please
build one and see if there are any messages in Xen dmesg also as a
result of the error (uisng `xl dmesg` if you don't have a serial
attached to the box). Posting full Linux and Xen dmesgs (Xen build
with debug=y) could also help.

PHYSDEVOP_map_pirq is failing but without further information it's
impossible to limit the scope of the issue (and whether the issue is
with PHYSDEVOP_map_pirq or some previous operation).

Thanks, Roger.