Re: [PATCH] i386/kvm: add NoNonArchitecturalCoreSharing Hyper-V enlightenment

[Paolo Bonzini <pbonzini@redhat.com>]

On 21/10/19 16:09, Vitaly Kuznetsov wrote:
>>> +    if (cpu->hyperv_no_nonarch_cs == ON_OFF_AUTO_ON) {
>>> +        env->features[FEAT_HV_RECOMM_EAX] |= HV_NO_NONARCH_CORESHARING;
>>> +    } else if (cpu->hyperv_no_nonarch_cs == ON_OFF_AUTO_AUTO) {
>> Do you want to make auto the default if "-cpu host,migratable=off"?  It
>> can be done on top so I started queueing this patch.
> Hm, one thing is that CPUID 0x40000004 doesn't exist if no Hyper-V
> enlightenments are passed so we'll probably have to modify your idea to
> "-cpu host,migratable=off,+any-hyperv-enlightenment" but then the
> question is how conservative are we, like if QEMU command line doesn't
> change can new CPUID flags appear or not? And we'll probably need a way
> to explicitly disable HV_NO_NONARCH_CORESHARING if needed.

I would defer to Eduardo on whether "migratable=off" would allow adding
new CPUID flags.  The follow-up question however is whether we would
benefit from a "+hyperv" option that enables all known Hyper-V
enlightenment for a given machine type.

Paolo