Maxim Levitsky mlevitsk@redhat.com 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.