I have an Ubuntu Linux VM that I've been using at 1920x1080 resolution, but I'd like it to be 3840x2160 for full resolution on my 4K monitors. The default QXL video driver doesn't support resolutions that high. But if I change the video model type to virtio in either XML or virt-manager, I can select resolutions up to 5120x2160. The only problem is selecting 3840x2160 or higher has a bug where it scales wrong, making the screen too large and cutting off the right third of the screen. VNC will scroll up and down to access the bottom area of the cutoff screen. But it's impossible to access the horizontal portion that's cut off. It behaves the same no matter what VNC client I use.

 

Also, the mouse cursor alignment is not scaled wrong, so clicks don't line up with where the mouse cursor appears, rather with the area of the screen that should be under the mouse if scaled properly. This makes it difficult to confirm the resolution or switch it back once confirmed, except with the keyboard.

 

Has anyone else experienced this? Which part of the virtualization stack would be responsible for this bug? The virtio video driver? And could that component be upgraded hopefully with a fix?

 

1920x1080

 

3840x2160 (right side cut off)

 

Note, the "Scale" option doesn't make a difference. 100% and 200% both behave the same way. I'd like 4K resolution with 200% scaling when using on my smaller 4K laptop monitor and lower scaling on my larger 4K external display.

Edited July 20, 20232 yr by Ancalagon

This appears to only be a problem with VNC. If I switch to SPICE, it scales correctly.