What does KVM do with model specific MSRs? Looks like you let the guest believe it was running on one of Sandy Bridge, Ivy Bridge, Haswell (Xeon). So, the core MCE code tried to enable extended error reporting. If there is a mode to have KVM let the guest think that it read/wrote MSR 0x17F, but actually, doesn't do it ... that would seem to be a reasonable thing to do here. -Tony