On Thu, Nov 10, 2016 at 06:57:21PM +0100, Paolo Bonzini wrote: > > > On 10/11/2016 12:48, Marcelo Tosatti wrote: > > Destination has to run the following logic: > > > > If (source has KVM_CAP_ADVANCE_CLOCK) > > use KVM_GET_CLOCK value > > Else > > read pvclock from guest > > > > To support migration from older QEMU versions which do not have > > KVM_CAP_ADVANCE_CLOCK (or new QEMU versions running on old > > hosts without KVM_CAP_ADVANCE_CLOCK). > > > > I don't see any clean way to give that information, except changing > > the migration format to pass "host: kvm_cap_advance_clock=true/false" > > information. > > If you make it only affect new machine types, you could transmit a dummy > clock value such as -1 if the source does not have KVM_CLOCK_TSC_STABLE. > > Paolo
Prefer a new subsection (which is fine since migration is broken anyway), because otherwise you have to deal with restoring s->clock from -1 to what was read at KVM_GET_CLOCK (in case migration fails).
