[Pkg-xen-devel] Bug#988333: Bug#988333: libxenmisc4.16: libxl fails to grant necessary I/O memory access for gfx_passthru of Intel IGD

[Chuck Zmudzinski]

On 3/7/22 10:39 AM, Marek Marczykowski-Górecki wrote:
>> You may be interested in this patch:
>> https://github.com/QubesOS/qubes-vmm-xen/blob/xen-4.14/patch-fix-igd-passthrough-with-linux-stubdomain.patch 
>>
>>
>> Qubes OS uses qemu-upstream in a Linux-based stubdomain, and with the
>> above patch applied, IGD passthrough works, at least to a Linux HVM.

It looks like there might also be some patches needed to Debian's Qemu, 
such as:

https://github.com/QubesOS/qubes-vmm-xen-stubdom-linux/blob/master/qemu/patches/0016-IGD-improve-legacy-vbios-handling.patch

which is not included in Debian's build of Qemu for sid/unstable. The 
necessary patches may be too aggressive for Debian's comfort, but I will 
look into it and see if I can get it working with Debian's upstream 
Qemu. It was a fairly minimal patch which required only expanding the 
I/O memory access by two pages to get this feature of Intel IGD legacy 
passthrough to Linux working with the ancient Qemu traditional device 
model, but I would much prefer Qemu upstream to the traditional device 
model, especially since Debian does not package the Qemu traditional 
device model for good reasons, given how old that code is.

Thanks, Marek, again for the tip.

Regards,

Chuck