I have two KVM servers where I'm doing GPU passthrough to a VM. Both are running linux 4.6.4. We're using an NVIDIA GPU which means I have to hide KVM (kvm=off, or <kvm><hidden state='on'/></kvm>). As a result, current_clocksource is tsc. ntpd shows a drift of ~0. So in seems that the tsc values the VM is getting are adjusted. On the same server, non-GPU VMs do get an unadjusted kvm-clock.