RE: [PATCH] KVM: x86: emulate wait-for-SIPI and SIPI-VMExit

[Qi, Yadong]

> There is a problem in this patch, in that this change is incorrect:
> 
> >
> > @@ -2847,7 +2847,8 @@ void kvm_apic_accept_events(struct kvm_vcpu
> *vcpu)
> >  	 */
> >  	if (kvm_vcpu_latch_init(vcpu)) {
> >  		WARN_ON_ONCE(vcpu->arch.mp_state ==
> KVM_MP_STATE_INIT_RECEIVED);
> > -		if (test_bit(KVM_APIC_SIPI, &apic->pending_events))
> > +		if (test_bit(KVM_APIC_SIPI, &apic->pending_events) &&
> > +		    !is_guest_mode(vcpu))
> >  			clear_bit(KVM_APIC_SIPI, &apic->pending_events);
> >  		return;
> >  	}
> 
> Here you're not trying to process a latched INIT; you just want to delay the
> processing of the SIPI until check_nested_events.
> 
> The change does have a correct part in it.  In particular,
> vmx_apic_init_signal_blocked should have been
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index
> 47b8357b9751..64339121a4f0 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7558,7 +7558,7 @@ static void enable_smi_window(struct kvm_vcpu
> *vcpu)
> 
>   static bool vmx_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
>   {
> -	return to_vmx(vcpu)->nested.vmxon;
> +	return to_vmx(vcpu)->nested.vmxon && !is_guest_mode(vcpu);
>   }
> 
>   static void vmx_migrate_timers(struct kvm_vcpu *vcpu)
> 
> to only latch INIT signals in root mode.  However, SIPI must be cleared
> unconditionally on SVM; the "!is_guest_mode" test in that case is incorrect.
> 
> The right way to do it is to call check_nested_events from
> kvm_apic_accept_events.  This will cause an INIT or SIPI vmexit, as required.
> There is some extra complication to read pending_events
> *before* kvm_apic_accept_events and not steal from the guest any INIT or SIPI
> that is sent after kvm_apic_accept_events returns.
> 
> Thanks to your test case, I will test a patch and send it.
> 
Thanks very much, Paolo.
BTW, I noticed another issue in sync_vmcs02_to_vmcs12():
vmcs12->guest_activity_state is not set properly when mp_state is INIT_RECEIVED.
I will correct it and send v2 of Patch 2/2.