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

[Felipe Reyes <freyes@suse.com>]

Hi,

On 08/05/2014 01:04 PM, Paolo Bonzini wrote:
> 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@redhat.com>
>> Suggested-by: "Zhang, Yang Z" <yang.z.zhang@intel.com>
>> Tested-by: Liu, RongrongX <rongrongx.liu@intel.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
>> ---
>> 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
>

I checked that the bug was still there using the latest version of 
linus' kernel (8e099d1) and it is, then I applied the patches you 
indicated and the problem went away. So those 2 patches fix the problem 
for me.

Best,