Invariant TSC documentation mentions that "invariant TSC will run at a
constant rate in all ACPI P-, C-. and T-states".

This is not the case if migration to a host with different TSC frequency
is allowed, or if savevm is performed. So block migration/savevm.
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
[AF+mtosatti: Updated error message]
Signed-off-by: NAndreas Färber <afaerber@suse.de>