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 09:13:56 +0000
From:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Jan Kiszka <jan.kiszka@...mens.com>
CC:	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

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.

> Paolo


Best regards,
Yang


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