Re: BUG: libxenlight fails to grant permission to access Intel IGD Opregion

[Chuck Zmudzinski <brchuckz@xxxxxxxxxxxx>]

On 3/11/22 8:47 AM, Chuck Zmudzinski wrote:
> On 3/11/2022 3:09 AM, Jan Beulich wrote:
>>
>> Thanks for this analysis. It looks quite plausible (but the question
>> of 2 vs 3 pages of course needs resolving).
>>
>>
>>
>
> After resolving the question of two vs. three pages, I will follow
> the process for submitting a patch against the latest staging.
>
> Qubes OS has a patch that uses three pages, and the
> igd.c pci file in Qemu's hw/vfio directory also specifies
> three pages, but if two is enough, that seems to be safer.
> I haven't checked yet to see if there is an official specification
> from Intel. I will start by looking in the Linux kernel i915
> driver code which might give a clue.

It looks like both in Xen and Qemu, it is agreed we need 3 pages

In Xen, we have:

From: Keir Fraser <keir@xxxxxxx>
Date: Thu, 10 Jan 2013 17:26:24 +0000 (+0000)
Subject: hvmloader: Allocate 3 pages for Intel GPU OpRegion passthrough.
X-Git-Tag: 4.3.0-rc1~546
X-Git-Url:
https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff_plain;h=408a9e56343b006c9e58a334f0b97dd2deedf9ac

hvmloader: Allocate 3 pages for Intel GPU OpRegion passthrough.

The 8kB region may not be page aligned, hence requiring 3 pages to
be mapped through.

Signed-off-by: Keir Fraser <keir@xxxxxxx>

Also Qemu upstream defines it as 3 pages:

https://xenbits.xen.org/gitweb/?p=qemu-xen.git;a=blob;f=hw/xen/xen_pt_graphics.c;h=a3bc7e39214b3d71c32c8386758fdef6ced5c0df;hb=a68d6d311c2d1fd9d2fa9a0768ea2353e8a79b42#l242

In Keir's commit, the OpRegion size was increased from 2 to
3 pages, so I think it is correct to use 3 pages in a proposed
patch.

In tools/firmware/hvmloader, there are header files that have
macros setting the address and size of the Intel IGD opregion.

So my only question is:

Is it proper to include header files from tools/firmware/hvmloader in
tools/libs/light/libxl_pci.c ?

Chuck