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

["mhbeyle@xxxxxxxx" <mhbeyle@xxxxxxxx>]

Thanks for the answers.

Chuck, I tried at the time to apply suggested patches to the software 
with no results. It is not clear that any of the current patches solve 
the problem.
I think there are two problems here: One, the virtual machine that 
creates xen uses QEMU and the UEFI bios is not able to communicate the 
resolution data to the system. Two, this kind of problem would be easily 
solved by virtualizing a more modern vga instead of the current cards 
(cirrus etc.) that are not recognized by the operating system when using 
UEFI and do not load specific drivers. For example, the problem is 
solved using qxl and a driver in Windows, but the qxl development is not 
complete and fails.
With limitations, it seems that the problem in QEMU is solved by 
changing the parameters in the BIOS and doing a warm/soft reboot. I 
don't know why, this can't be done in xen. The settings are never saved 
and the reboot, at least in windows 10, is always a cold one (xen 
destroys the virtual machine and recreates it. The soft reboot parameter 
hangs the vm).
Regards.

__________
MhBeyle ___


El 21/09/2022 a las 14:00, xen-users-request@xxxxxxxxxxxxxxxxxxxx escribió:
> Message: 1
> Date: Mon, 19 Sep 2022 19:12:57 +0200
> From: Stefan Kadow <pub@xxxxxxxx>
> To: xen-users@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: xen ovmf/uefi firmware does not save screen resolution
> Message-ID: <aea59c2c-e4d4-15d1-c328-2d3febc7639b@xxxxxxxx>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> Am 19.09.22 um 18:03 schrieb Chuck Zmudzinski:
> > 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
> I encountered this problem two years ago. I suspected a problem with
> Qemu and reported it on a mailing list, but never got a response:
>
> https://lists.nongnu.org/archive/html/qemu-discuss/2020-09/msg00010.html
>
> Best regards.
> Stefan