bhyve clock problem, solved by kern.timecounter.hardware="TSC-low" in /etc/sysctl.conf

[Ryan Stone]

Using the TSC as the default timecounter in a VM is dangerous.  On some
hardware, the TSC is not synchronized across all CPU cores.  This means
that if a VM migrates from one core to another, it could see the
timecounter value go backwards.  Time jumping backwards can cause all kinds
of hilarity.

What's really needed is for bhyve to support KVM clock or a similar scheme
(brianv@ might also still need to commit the guest side of KVM clock as
well).