Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

[Yang Zhang <yang.zhang.wz@gmail.com>]

On 2016/1/21 13:33, Wu, Feng wrote:
>
>
>> -----Original Message-----
>> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
>> owner@vger.kernel.org] On Behalf Of Yang Zhang
>> Sent: Thursday, January 21, 2016 1:24 PM
>> To: Wu, Feng <feng.wu@intel.com>; pbonzini@redhat.com;
>> rkrcmar@redhat.com
>> Cc: linux-kernel@vger.kernel.org; kvm@vger.kernel.org
>> Subject: Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-
>> priority interrupts
>>
>> On 2016/1/20 9:42, Feng Wu wrote:
>>> Use vector-hashing to deliver lowest-priority interrupts, As an
>>> example, modern Intel CPUs in server platform use this method to
>>> handle lowest-priority interrupts.
>>>
>>> Signed-off-by: Feng Wu <feng.wu@intel.com>
>>> ---
>>>    bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic
>> *src,
>>>    		struct kvm_lapic_irq *irq, int *r, unsigned long *dest_map)
>>>    {
>>> @@ -727,21 +743,51 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm
>> *kvm, struct kvm_lapic *src,
>>>
>>>    		dst = map->logical_map[cid];
>>>
>>> -		if (kvm_lowest_prio_delivery(irq)) {
>>> +		if (!kvm_lowest_prio_delivery(irq))
>>> +			goto set_irq;
>>> +
>>> +		if (!kvm_vector_hashing_enabled()) {
>>>    			int l = -1;
>>>    			for_each_set_bit(i, &bitmap, 16) {
>>>    				if (!dst[i])
>>>    					continue;
>>>    				if (l < 0)
>>>    					l = i;
>>> -				else if (kvm_apic_compare_prio(dst[i]->vcpu,
>> dst[l]->vcpu) < 0)
>>> +				else if (kvm_apic_compare_prio(dst[i]->vcpu,
>>> +							dst[l]->vcpu) < 0)
>>>    					l = i;
>>>    			}
>>> -
>>>    			bitmap = (l >= 0) ? 1 << l : 0;
>>> +		} else {
>>> +			int idx = 0;
>>> +			unsigned int dest_vcpus = 0;
>>> +
>>> +			dest_vcpus = hweight16(bitmap);
>>> +			if (dest_vcpus == 0)
>>> +				goto out;
>>> +
>>> +			idx = kvm_vector_2_index(irq->vector,
>>> +				dest_vcpus, &bitmap, 16);
>>> +
>>> +			/*
>>> +			 * We may find a hardware disabled LAPIC here, if
>> that
>>> +			 * is the case, print out a error message once for each
>>> +			 * guest and return.
>>> +			 */
>>> +			if (!dst[idx-1] &&
>>> +				(kvm->arch.disabled_lapic_found == 0)) {
>>> +				kvm->arch.disabled_lapic_found = 1;
>>> +				printk(KERN_ERR
>>> +					"Disabled LAPIC found during irq
>> injection\n");
>>> +				goto out;
>>
>> What does "goto out" mean? Inject successfully or fail? According the
>> value of ret which is set to ture here, it means inject successfully but
>> i = -1.
>>
>
> Oh, I didn't notice 'ret' is initialized to true, I thought it was initialized
> to false like another function, I should add a "ret = false' here. We should
> failed to inject the interrupt since hardware disabled LAPIC is found.

I remember we have discussed that even the LAPIC is software disabled, 
it still can respond to some interrupts like INIT, NMI, SMI, and SIPI 
messages. Isn't current logic still problematically?

-- 
best regards
yang