Created attachment 131340 [details]
dmesg dump (complete)

I experience random (relatively low occurrence ~ twice a week) graphic lockups.
Video is not updated, mouse is moving but no interaction is possible either
with mouse or keyboard.

System is somewhat alive and I can login via ssh.

I attach a complete dmesg dump taken via ssh.

Attempting to kill xorg to restart it resulted in a complete lockup (ssh timed
out) and I had to brutally power-cycle the machine.

System is an up-to-date debian testing (stretch).

At the time of freeze I had one VirtualBox client (Win7) open but inactive
(window minimized).

I will be available to give further info, if required.