From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v2 2/5] KVM: nVMX: Re-evaluate L1 pending events when
 running L2 and L1 got posted-interrupt
Date: Mon, 11 Dec 2017 23:53:51 +0100
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On 06/12/2017 19:52, Radim Krčmář wrote:
>>  		smp_mb__after_atomic();
>>  		max_irr = kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
> I think the optimization (partly livelock protection) is not worth the
> overhead of two IRR scans for non-nested guests.  Please make
> kvm_apic_update_irr() return both prev_max_irr and max_irr in one pass.

You could also return max_irr in an int*, and give the function a "bool"
return type for max_irr > prev_max_irr.  That is more efficient because
you can do the check in the "if (pir_val)" conditional of
__kvm_apic_update_irr.

Paolo

>> +
>> +		/*
>> +		 * If we are running L2 and L1 has a new pending interrupt
>> +		 * which can be injected, we should re-evaluate
>> +		 * what should be done with this new L1 interrupt.
>> +		 */
>> +		if (is_guest_mode(vcpu) && (max_irr > prev_max_irr))
>> +			kvm_make_request(KVM_REQ_EVENT, vcpu);
> We don't need anything from KVM_REQ_EVENT and only use it to abort the
> VM entry, kvm_vcpu_exiting_guest_mode() is better for that.
> 
>>  	} else {
>> -		max_irr = kvm_lapic_find_highest_irr(vcpu);
>> +		max_irr = prev_max_irr;
>>  	}
>> +
>>  	vmx_hwapic_irr_update(vcpu, max_irr);
> We also should just inject the interrupt if L2 is run without
> nested_exit_on_intr(), maybe reusing the check in vmx_hwapic_irr_update?