Re: [PATCH v2 2/2] KVM: nVMX: fix acknowledge interrupt on exit when APICv is in use

[Paolo Bonzini]

Il 05/08/2014 06:42, Wanpeng Li ha scritto:
> After commit 77b0f5d (KVM: nVMX: Ack and write vector info to intr_info
> if L1 asks us to), "Acknowledge interrupt on exit" behavior can be
> emulated. To do so, KVM will ask the APIC for the interrupt vector if
> during a nested vmexit if VM_EXIT_ACK_INTR_ON_EXIT is set.  With APICv,
> kvm_get_apic_interrupt would return -1 and give the following WARNING:
> 
> Call Trace:
>  [<ffffffff81493563>] dump_stack+0x49/0x5e
>  [<ffffffff8103f0eb>] warn_slowpath_common+0x7c/0x96
>  [<ffffffffa059709a>] ? nested_vmx_vmexit+0xa4/0x233 [kvm_intel]
>  [<ffffffff8103f11a>] warn_slowpath_null+0x15/0x17
>  [<ffffffffa059709a>] nested_vmx_vmexit+0xa4/0x233 [kvm_intel]
>  [<ffffffffa0594295>] ? nested_vmx_exit_handled+0x6a/0x39e [kvm_intel]
>  [<ffffffffa0537931>] ? kvm_apic_has_interrupt+0x80/0xd5 [kvm]
>  [<ffffffffa05972ec>] vmx_check_nested_events+0xc3/0xd3 [kvm_intel]
>  [<ffffffffa051ebe9>] inject_pending_event+0xd0/0x16e [kvm]
>  [<ffffffffa051efa0>] vcpu_enter_guest+0x319/0x704 [kvm]
> 
> If enabling APIC-v, all interrupts to L1 are delivered through APIC-v.
> But when L2 is running, external interrupt will casue L1 vmexit with
> reason external interrupt. Then L1 will pick up the interrupt through
> vmcs12. when L1 ack the interrupt, since the APIC-v is enabled when
> L1 is running, so APIC-v hardware still will do vEOI updating. The problem
> is that the interrupt is delivered not through APIC-v hardware, this means
> SVI/RVI/vPPR are not setting, but hardware required them when doing vEOI
> updating. The solution is that, when L1 tried to pick up the interrupt
> from vmcs12, then hypervisor will help to update the SVI/RVI/vPPR to make
> sure the following vEOI updating and vPPR updating corrently.
>     
> Also, since interrupt is delivered through vmcs12, so APIC-v hardware will
> not cleare vIRR and hypervisor need to clear it before L1 running.
> 
> Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Suggested-by: "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>
> Tested-by: Liu, RongrongX <rongrongx.liu@xxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
> ---
> v1 -> v2:
>  * reusing kvm_get_apic_interrupt here (by modifying kvm_cpu_get_interrupt, 
>    apic_set_isr and apic_clear_irr)
> 
>  arch/x86/kvm/irq.c   |  2 +-
>  arch/x86/kvm/lapic.c | 52 +++++++++++++++++++++++++++++++++++++++-------------
>  2 files changed, 40 insertions(+), 14 deletions(-)
> 
> 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 */
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 3855103..08e8a89 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -352,25 +352,46 @@ static inline int apic_find_highest_irr(struct kvm_lapic *apic)
>  
>  static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)
>  {
> -	apic->irr_pending = false;
> +	struct kvm_vcpu *vcpu;
> +
> +	vcpu = apic->vcpu;
> +
>  	apic_clear_vector(vec, apic->regs + APIC_IRR);
> -	if (apic_search_irr(apic) != -1)
> -		apic->irr_pending = true;
> +	if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
> +		/* try to update RVI */
> +		kvm_make_request(KVM_REQ_EVENT, vcpu);
> +	else {
> +		vec = apic_search_irr(apic);
> +		apic->irr_pending = (vec != -1);
> +	}
>  }
>  
>  static inline void apic_set_isr(int vec, struct kvm_lapic *apic)
>  {
> -	/* Note that we never get here with APIC virtualization enabled.  */
> +	struct kvm_vcpu *vcpu;
> +
> +	if (__apic_test_and_set_vector(vec, apic->regs + APIC_ISR))
> +		return;
> +
> +	vcpu = apic->vcpu;
>  
> -	if (!__apic_test_and_set_vector(vec, apic->regs + APIC_ISR))
> -		++apic->isr_count;
> -	BUG_ON(apic->isr_count > MAX_APIC_VECTOR);
>  	/*
> -	 * ISR (in service register) bit is set when injecting an interrupt.
> -	 * The highest vector is injected. Thus the latest bit set matches
> -	 * the highest bit in ISR.
> +	 * With APIC virtualization enabled, all caching is disabled
> +	 * because the processor can modify ISR under the hood.  Instead
> +	 * just set SVI.
>  	 */
> -	apic->highest_isr_cache = vec;
> +	if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
> +		kvm_x86_ops->hwapic_isr_update(vcpu->kvm, vec);
> +	else {
> +		++apic->isr_count;
> +		BUG_ON(apic->isr_count > MAX_APIC_VECTOR);
> +		/*
> +		 * ISR (in service register) bit is set when injecting an interrupt.
> +		 * The highest vector is injected. Thus the latest bit set matches
> +		 * the highest bit in ISR.
> +		 */
> +		apic->highest_isr_cache = vec;
> +	}
>  }
>  
>  static inline int apic_find_highest_isr(struct kvm_lapic *apic)
> @@ -1627,11 +1648,16 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
>  	int vector = kvm_apic_has_interrupt(vcpu);
>  	struct kvm_lapic *apic = vcpu->arch.apic;
>  
> -	/* Note that we never get here with APIC virtualization enabled.  */
> -
>  	if (vector == -1)
>  		return -1;
>  
> +	/*
> +	 * We get here even with APIC virtualization enabled, if doing
> +	 * nested virtualization and L1 runs with the "acknowledge interrupt
> +	 * on exit" mode.  Then we cannot inject the interrupt via RVI,
> +	 * because the process would deliver it through the IDT.
> +	 */
> +
>  	apic_set_isr(vector, apic);
>  	apic_update_ppr(apic);
>  	apic_clear_irr(vector, apic);
> 

Thanks, this looks good.  Felipe, can you test this patch together with
http://article.gmane.org/gmane.linux.kernel/1762356/raw please?

Paolo
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