VirtualBox 5 with xf86-video-ati-7.5.0,1

[Warren Block]

After the recent X update, starting VirtualBox 5 VMs triggers a system 
panic within minutes or hours.

I'm running it on FreeBSD 12-current, at r313081 from yesterday. 
However, this seems to be a problem with VirtualBox. As long as a VM is 
not started, things go fine.  (Yes, the kernel module has been updated.)

Can anyone using 11-Release or 11-Stable with the recent xorg updates 
verify whether VirtualBox 5 is still usable there?  Of particular 
interest would be systems using Radeon video cards.

If people know of an easy, preferably automatic way to convert numerous 
VirtualBox VMs for use with bhyve, that would also be interesting.