Re: [PATCH v7 01/15] nEPT: Support LOAD_IA32_EFER entry/exit controls for L1

[Gleb Natapov <gleb@redhat.com>]

On Mon, Aug 05, 2013 at 07:48:54AM -0400, Paolo Bonzini wrote:
> > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > > index e999dc7..27efa6a 100644
> > > --- a/arch/x86/kvm/vmx.c
> > > +++ b/arch/x86/kvm/vmx.c
> > > @@ -2198,7 +2198,8 @@ static __init void nested_vmx_setup_ctls_msrs(void)
> > >  #else
> > >         nested_vmx_exit_ctls_high = 0;
> > >  #endif
> > > -       nested_vmx_exit_ctls_high |= VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR;
> > > +       nested_vmx_exit_ctls_high |= (VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
> > > +                                     VM_EXIT_LOAD_IA32_EFER);
> > 
> > Gleb, why we don't need to check whether host supports
> > VM_EXIT_LOAD_IA32_EFER here, as what you noted in my
> > VM_EXIT_LOAD_IA32_PAT patch?
> 
> The host can also emulate VM_EXIT_LOAD_IA32_EFER using the
> VM-exit MSR-load feature.  If neither EFER save/load nor
> MSR save/load are available, I believe you are right and
> the feature should not be available in nested VMX.
As far as I can tell MSR save/load is not optional.

--
			Gleb.