Re: xen ovmf/uefi firmware does not save screen resolution

[Chuck Zmudzinski <brchuckz@xxxxxxxxxxxx>]

On 9/18/2022 11:52 PM, Chuck Zmudzinski wrote:
> On 9/15/2022 10:55 AM, mhbeyle@xxxxxxxx wrote:
> > Hello Xen users ...
> >
> > I have a problem with a hvm domU that uses ovmf/uefi firmware ans loads a 
> > windows 10 SO.
> >
> > When windows loads, screen resolution is always 800x600 mode and there is 
> > no possibility of switching to another one.
> > So I change resolution into UEFI bios (Tiano Core), save and restart with 
> > no change. Screen resolution is always the same, on boot loading and 
> > windows.
> >
> > I have tried changing several settings in the configuration file (vga, 
> > videoram) with no results.
> >
> > Screen resolution can be changed in Legacy BIOS mode.
> >
> >
> > Any idea what I need to look at? I am completely lost with this issue ..
> >
> > Dom0 is running under Debian (5.10.0-17-amd64) and xen version is 4.14.5 
> > (xen-3.0-x86_64).
> >
> > Thank you very much in advance and best regards.
> >
> > ------------------
> > MhBeyle ___
>
> I think I have heard about this problem, but I am not sure what the answer is.
> That is why I always use the Legacy BIOS mode with Xen HVM. Just speculating,
> it might be because the Xen HVM device model, Qemu, has the part that
> supports Xen HVM, but it emulates a very old type of PC, I think twenty-five
> years old or something like that. The emulation if you use Qemu with
> KVM instead of Xen is of a newer PC like only twelve years old or
> so, when the all the PCs had UEFI. Just a thought about the reason.
>
> I also don't know if Xen HVM with Qemu emulation works for a Windows
> 11 HVM. My guess is it would not, but maybe if the Xen developers fix that
> by the time support for Windows 10 ends, they might also fix this problem
> with the UEFI screen resolution because I think in Windows 11 UEFI is required
> AFAIK.
>
> The best chance might be for you to work on it and try to find a fix yourself.
> It is not easy to find the technical information to do it, but if you start
> experimenting and reading articles online about it you can learn how to do it.
> Debian is a good platform for building the packages. You probably will want to
> at least learn to build and test patches to Xen, Qemu, the Linux kernel, and 
> ovmf
> packages. It is a complicated problem because all those packages have to work
> together nicely. Start by researching the technical specifications for UEFI, 
> it
> is quite different from legacy BIOS.
>
> Best regards,
>
> Chuck
>

Just a couple of more tips on working on this problem using Debian. I would 
recommend
using Debian unstable instead of Debian stable, so that you can be working on 
the
latest versions of the upstream packages. There also was a patch set proposed 
for
Qemu and Xen to update the emulation to the same type of PC that Qemu uses
with KVM over four years ago, and it was discussed on xen-devel but never made
it into Xen and Qemu. These patches and the discussions there would probably
be helpful:

https://lists.xenproject.org/archives/html/xen-devel/2018-03/msg01176.html

I am not sure if this problem is fixed on KVM/Qemu, but I would definitely 
check and see,
and if so, the KVM solution can guide your work on patching Xen and Qemu to fix 
this.

Best regards,

Chuck