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

[Paolo Bonzini <pbonzini@redhat.com>]

> > 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.