Re: [PATCH] KVM: vmx: restore MSR_IA32_DEBUGCTLMSR after VMEXIT

[Gleb Natapov <gleb@redhat.com>]

On Sun, Aug 12, 2012 at 04:22:59PM +0300, Avi Kivity wrote:
> On 08/12/2012 04:12 PM, Gleb Natapov wrote:
> > MSR_IA32_DEBUGCTLMSR is zeroed on VMEXIT. Restore it to the correct
> > value.
> > 
> > @@ -6222,6 +6222,7 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
> >  static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
> >  {
> >  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> > +	unsigned long debugctlmsr;
> >  
> >  	if (is_guest_mode(vcpu) && !vmx->nested.nested_run_pending) {
> >  		struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> > @@ -6261,6 +6262,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
> >  		vmx_set_interrupt_shadow(vcpu, 0);
> >  
> >  	atomic_switch_perf_msrs(vmx);
> > +	debugctlmsr = get_debugctlmsr();
> 
> How expensive is this?  We may want a follow-on patch to cache it in a
> per-cpu variable.
> 
I have patches ready. I couldn't measure any overhead of the
rdmsr(MSR_IA32_DEBUGCTLMSR).

--
			Gleb.