Il 12/08/2014 21:29, Eduardo Habkost ha scritto: > On Tue, Aug 12, 2014 at 09:12:00PM +0200, Paolo Bonzini wrote: >> Il 12/08/2014 20:55, Eduardo Habkost ha scritto: >>> This makes the CPUID data change under the guest's feet during >>> live-migration. >>> >>> Adding compat code to ensure older machine-types keep the old behavior >>> is necessary, but in this specific case it is mostly harmless because >>> 0x0 is documented as being equivalent to 0x40000001. >>> >>> (But I don't know how guests are supposed to behave when they see >>> CPUID[KVM_CPUID_SIGNATURE_NEXT].EAX==0.) >> >> The only obvious thing to do would be to treat it as 0x40000101. > > I just want to be sure the guests really do that. If we know guests > won't do anything different with the CPUID change, I won't mind having > no compat code for this. >
Considering that only two leaves are defined for KVM, and both are mandatory I don't think current guests have any reason to look at CPUID[KVM_CPUID_SIGNATURE | kvm_base].EAX at all. Paolo
