Bug#860946: drm problems with vram size / virt-manager display size at boot

[Daniel Pocock <daniel@pocock.pro>]

Package: libdrm2
Version: 2.4.74-1
Severity: important

This problem was observed on a virtual machine running stretch inside a
KVM environment.  The machine had been a fresh install of stretch in
January 2017, updated with apt in the last 24 hours.

Last time I used my VM, I had stretched the virt-manager window to be
quite large.  spice-vdagent is running in the VM and the screen size
adapted and it was working fine.  My physical display is a 4k monitor.

Next time I booted the VM, the gdm login didn't appear, just a dark gray
background, it appeared to be sized at one of the default resolutions
like 800x600.

I connected to the VM with ssh and found this in journalctl:

test-vm1 kernel: [drm:qxl_crtc_mode_set [qxl]] *ERROR* Mode doesn't fit
in vram size (vgamem)
test-vm1 kernel: [drm:drm_crtc_helper_set_config [drm_kms_helper]]
*ERROR* failed to set mode on [CRTC:27:crtc-0]


I shut down the VM and used "virsh edit test-vm1" to find the vram
setting and increased it from 64M to 256M.

I observed the same problem on the next boot.

Then, while the gray background was visible, I tried reducing the size
of the virt-manager window.  As the virt-manager got smaller, the gdm
login box suddenly appeared.  After logging in, I was able to expand the
virt-manager window again and it continued working fine.

It would be useful to

a) understand why this happens at boot/login time but it works fine at
this resolution after login

b) improve gdm, wayland or whatever so it shows something more
meaningful than a gray background