q: incorrect register emulation mask for Xen PCI passthrough?

[Michael Tokarev <mjt@xxxxxxxxxx>]

There's a debian bugreport open - now against qemu - 
https://bugs.debian.org/988333 -
which initially said VGA Intel IGD Passthrough to Debian Xen HVM DomUs not 
working
but worked okay with windows DomUs.

The most interesting comment in there is the last one, 
https://bugs.debian.org/988333#146 ,
which sums it all up and provides a patch for the issue, at
https://github.com/QubesOS/qubes-vmm-xen-stubdom-linux/pull/3/commits/ab2b4c2ad02827a73c52ba561e9a921cc4bb227c
which is from 2017 (!).

I wonder if we should apply this one upstream, or if it is somehow incorrect
fix, should fix this particular issue the right way.  It's 5 years old already
and people are still suffering... :)

Thanks,

/mjt