Fedora 24 issues on VirtualBox

As of some recent upgrades to my F24 VM (running under VirtualBox), my system would not boot properly any more, getting errors like

NMI watchdog: BUG: soft lockup - CPU#0 stuck


I couldn't find any details as to why this was, other than someone having similar issues with a bad GPU card (not under a VM). I checked my display settings for the VM, which had the minimum recommended setting of 21MB. This ought to have been plenty, since I run my Linux system in a head-less mode (no display etc.). However, Linux must have changed something, cause this no longer worked, but bumping the GPU memory to 32MB seems to have fixed it. Bizarre.