linux-kernel - Re: [PATCH 2/3] KVM: nVMX: Fix fail to get nested ack intr's vector during nested vmexit

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Date:	Thu, 17 Jul 2014 18:01:30 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
Cc:	Jan Kiszka <jan.kiszka@...mens.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, Bandan Das <bsd@...hat.com>,
	"Hu, Robert" <robert.hu@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] KVM: nVMX: Fix fail to get nested ack intr's vector
 during nested vmexit

On Thu, Jul 17, 2014 at 09:13:56AM +0000, Zhang, Yang Z wrote:
>Paolo Bonzini wrote on 2014-07-17:
>> Il 17/07/2014 06:56, Wanpeng Li ha scritto:
>>>  	    && nested_exit_intr_ack_set(vcpu)) {
>>>  		int irq = kvm_cpu_get_interrupt(vcpu);
>>> +
>>> +		if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
>>> +			irq = kvm_get_apic_interrupt(vcpu);
>> 
>> There's something weird in this patch.  If you "inline"
>> kvm_cpu_get_interrupt, what you get is this:
>> 
>>          int irq;
>> 	/* Beginning of kvm_cpu_get_interrupt... */
>>          if (!irqchip_in_kernel(v->kvm))
>>                  irq = v->arch.interrupt.nr;
>> 	else {
>> 	        irq = kvm_cpu_get_extint(v); /* PIC */
>> 	        if (!kvm_apic_vid_enabled(v->kvm) && irq == -1)
>> 			irq = kvm_get_apic_interrupt(v); /* APIC */
>> 	}
>> 
>> 	/* kvm_cpu_get_interrupt done. */
>> 	if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
>> 		irq = kvm_get_apic_interrupt(vcpu);
>> 
>> There are just two callers of kvm_cpu_get_interrupt, and the other is
>> protected by kvm_cpu_has_injectable_intr so it won't be executed if
>> virtual interrupt delivery is enabled.  So you patch is effectively the same as this:
>> 
>> diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c index
>> bd0da43..a1ec6a5 100644 --- a/arch/x86/kvm/irq.c +++
>> b/arch/x86/kvm/irq.c @@ -108,7 +108,7 @@ int
>> kvm_cpu_get_interrupt(struct kvm_vcpu *v)
>> 
>>   	vector = kvm_cpu_get_extint(v);
>> -	if (kvm_apic_vid_enabled(v->kvm) || vector != -1)
>> +	if (vector != -1)
>>   		return vector;			/* PIC */
>>   
>>   	return kvm_get_apic_interrupt(v);	/* APIC */
>> But in kvm_get_apic_interrupt I have just added this comment:
>> 
>>          /* Note that we never get here with APIC virtualization
>> 	 * enabled.  */
>> 
>> because kvm_get_apic_interrupt calls apic_set_isr, and apic_set_isr
>> must never be called with APIC virtualization enabled either.  With
>> APIC virtualization enabled, isr_count is always 1, and
>> highest_isr_cache is always -1, and apic_set_isr breaks both of these invariants.
>> 
>
>You are right. kvm_lapic_find_highest_irr should be the right one.

That is my original proposal solution of this bug. However, what I concern 
after more think is since kvm_lapic_find_highest_irr will not clear
irr, if the intr will be injected by kvm_86_ops->hwapic_irr_update(vcpu, 
kvm_lapic_find_highest_irr(vcpu)) which called by vcpu_enter_guest() again? 

Any idea, Paolo?

Regards,
Wanpeng Li 

>
>> Paolo
>
>
>Best regards,
>Yang
>

View attachment "0001-fix-warning.patch" of type "text/x-diff" (3429 bytes)