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

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Message-ID: <56A0734E.8050508@gmail.com>
Date:	Thu, 21 Jan 2016 13:57:34 +0800
From:	Yang Zhang <yang.zhang.wz@...il.com>
To:	"Wu, Feng" <feng.wu@...el.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"rkrcmar@...hat.com" <rkrcmar@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver
 lowest-priority interrupts

On 2016/1/21 13:46, Wu, Feng wrote:
>
>
>> -----Original Message-----
>> From: Yang Zhang [mailto:yang.zhang.wz@...il.com]
>> Sent: Thursday, January 21, 2016 1:43 PM
>> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
>> rkrcmar@...hat.com
>> Cc: linux-kernel@...r.kernel.org; kvm@...r.kernel.org
>> Subject: Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-
>> priority interrupts
>>
>> On 2016/1/21 13:33, Wu, Feng wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
>>>> owner@...r.kernel.org] On Behalf Of Yang Zhang
>>>> Sent: Thursday, January 21, 2016 1:24 PM
>>>> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
>>>> rkrcmar@...hat.com
>>>> Cc: linux-kernel@...r.kernel.org; kvm@...r.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@...el.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?
>
> I don't think there are problems, here we only cover lowest-priority mode.

Does Intel SDM said those interrupts cannot be delivered on 
lowest-priority mode?

CC Jun.

Hi Jun,

Do you know whether INIT, NMI, SMI, and SIPI can be delivered through 
lowest-priority mode? I didn't find SDM says no.

-- 
best regards
yang