Guest display resolution cannot be changed when using certain graphics/interface combinations

[johannes]

Guest display resolution cannot be changed with certain virtual graphics card (-vga) and interface (-display) combinations.

For example, resolution changing doesn't work with the following QEMU start commands, it resets to the default resolution immediately:

QXL with SDL interface:
qemu-system-x86_64 -enable-kvm -m 6G -cpu host -smp 3 -cdrom ./linux/kubuntu-20.04-desktop-amd64.iso -boot d -vga qxl -soundhw hda -display sdl

QXL with GTK interface:
qemu-system-x86_64 -enable-kvm -m 6G -cpu host -smp 3 -cdrom ./linux/kubuntu-20.04-desktop-amd64.iso -boot d -vga qxl -soundhw hda -display gtk

QXL with "remote" SPICE interface via unix socket:
qemu-system-x86_64 -enable-kvm -m 6G -cpu host -smp 3 -cdrom ./linux/kubuntu-20.04-desktop-amd64.iso -boot d -soundhw hda -vga qxl -device virtio-serial-pci -device virtserialport,chardev=spicechannel0,name=com.redhat.spice.0 -chardev spicevmc,id=spicechannel0,name=vdagent -spice unix,addr=/tmp/vm_spice.socket,disable-ticketing

for "remote" access:
remote-viewer spice+unix:///tmp/vm_spice.socket

Other tested combinations:
-- virtio + SDL (GL on): works!
-- virtio + GTK (GL on): does not work properly. The resolution is changed but window size is not so the guest screen will look like garbage.
-- vmware: The initial Kubuntu setup screen is visible but booting does not progress to the desktop
-- std + GTK: works!
-- std + SDL: works!

QEMU version: 5.1.0
Guest: Kubuntu 20.04 64-bit (live) with 5.4.0-26 kernel; may occur with other guests as well
Host: Arch Linux, with KDE desktop

[Thomas Huth (th-huth)]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting the bug state to "Incomplete" now.

If the bug has already been fixed in the latest upstream version of QEMU,
then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here is still
valid, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

    https://gitlab.com/qemu-project/qemu/-/issues

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" or "Confirmed" within the next 60 days (other-
wise it will get closed as "Expired"). We will then eventually migrate
the ticket automatically to the new system (but you won't be the reporter
of the bug in the new system and thus you won't get notified on changes
anymore).

Thank you and sorry for the inconvenience.

[Launchpad Janitor (janitor)]

[Expired for QEMU because there has been no activity for 60 days.]