Maxim Levitsky [off-list ref] writes:

But other than that I don't mind making TSC offset global per VM thing.
Paulo, what do you think about this?

Not Paolo here but personally I'd very much prefer we go this route but
unsynchronized TSCs are, unfortunately, still a thing: I was observing
it on an AMD Epyc server just a couple years ago (cured with firmware
update). We try to catch such situation in KVM instead of blowing up but
this may still result in subtle bugs I believe. Maybe we would be better
off killing all VMs in case TSC ever gets unsynced (by default).

Another thing to this bucket is kvmclock which is currently per-cpu. If
we forbid TSC to un-synchronize (he-he), there is no point in doing
that. We can as well use e.g. Hyper-V TSC page method which is
per-VM. Creating another PV clock in KVM may be a hard sell as all
modern x86 CPUs support TSC scaling (in addition to TSC offsetting which
is there for a long time) and when it's there we don't really need a PV
clock to make migration possible.

-- 
Vitaly