On Wed, 08 Mar 2023 07:53:46 +0000, Oliver Upton <oliver.upton@xxxxxxxxx> wrote: > > > I certainly agree that (2a) is highly desirable to get existing VMMs to > > 'do the right thing' for free. Playing devil's advocate, would this not > > also break the tracing example you've given of correlating timestamps > > between the host and guest? I wouldn't expect a userspace + VM tracing > > contraption to live migrate but restoring from a snapshot seems > > plausible. > > The problem I'm alluding to here is that the VMM will save/restore > the physical counter value and cause KVM to offset the physical counter. > Live migration is a pretty obvious example, but resuming from a snapshot > after resetting a system be similarly affected. My take on this is that if you have produced the snapshot on a pre-CNTPCT host, there will be no change in behaviour. If you've produced the snapshot on a new host, you get the new behaviour. I am willing to be accommodating to the use case, but only to a certain extent! ;-) M. -- Without deviation from the norm, progress is not possible.
