Re: [libvirt] Exporting kvm_max_guest_tsc_khz to userspace (was Re: [PATCH 4/4] kvm: Allow migration with invtsc)

On 08/01/2017 21:28, Eduardo Habkost wrote: >> Well just export KVM_GET_TSC_KHZ in a QMP command right? Its pretty >> easy. >> >> Let me know if you need any help coding or testing. > I just found out that KVM doesn't provide something that QEMU and > libvirt need: the value of kvm_max_guest_tsc_khz. Without it, we > have no way to know if a given VM is really migratable to a host. > > Could we add a KVM_CAP_MAX_TSC_KHZ capability for that? The ratio is really quite high, 256x the host frequency for AMD and 65536x for Intel. Anything below 2^32 Hz (above that, there would probably be other failures) is safe.