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

[Liu, RongrongX]

> -----Original Message-----
> From: kvm-owner@xxxxxxxxxxxxxxx [mailto:kvm-owner@xxxxxxxxxxxxxxx]
> On Behalf Of Wanpeng Li
> Sent: Friday, August 01, 2014 4:12 PM
> To: Paolo Bonzini; Jan Kiszka
> Cc: Marcelo Tosatti; Gleb Natapov; Bandan Das; Zhang, Yang Z;
> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Wanpeng Li
> Subject: [PATCH 2/2] KVM: nVMX: fix acknowledge interrupt on exit when
> APICv is in use
> 
> 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>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>

Tested-by:  Liu, RongrongX <rongrongx.liu@xxxxxxxxx>

> ---
>  arch/x86/kvm/lapic.c | 18 ++++++++++++++++++  arch/x86/kvm/lapic.h |  1
> +
>  arch/x86/kvm/vmx.c   | 10 ++++++++++
>  3 files changed, 29 insertions(+)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index
> 3855103..06942b9 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -534,6 +534,24 @@ static void apic_set_tpr(struct kvm_lapic *apic, u32
> tpr)
>  	apic_update_ppr(apic);
>  }
> 
> +int kvm_lapic_ack_apicv(struct kvm_vcpu *vcpu) {
> +	struct kvm_lapic *apic = vcpu->arch.apic;
> +	int vec;
> +
> +	vec = kvm_apic_has_interrupt(vcpu);
> +
> +	if (vec == -1)
> +		return vec;
> +
> +	apic_set_vector(vec, apic->regs + APIC_ISR);
> +	apic_update_ppr(apic);
> +	apic_clear_vector(vec, apic->regs + APIC_IRR);
> +
> +	return vec;
> +}
> +EXPORT_SYMBOL_GPL(kvm_lapic_ack_apicv);
> +
>  int kvm_apic_match_physical_addr(struct kvm_lapic *apic, u16 dest)  {
>  	return dest == 0xff || kvm_apic_id(apic) == dest; diff --git
> a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h index 6a11845..ead1392
> 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -169,5 +169,6 @@ static inline bool kvm_apic_has_events(struct
> kvm_vcpu *vcpu)  }
> 
>  bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector);
> +int kvm_lapic_ack_apicv(struct kvm_vcpu *vcpu);
> 
>  #endif
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index
> b8122b3..c604f3c 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8766,6 +8766,16 @@ static void nested_vmx_vmexit(struct kvm_vcpu
> *vcpu, u32 exit_reason,
>  	if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
>  	    && nested_exit_intr_ack_set(vcpu)) {
>  		int irq = kvm_cpu_get_interrupt(vcpu);
> +
> +		if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm)) {
> +			irq = kvm_lapic_ack_apicv(vcpu);
> +			if (irq >= 0) {
> +				vmx_hwapic_isr_update(vcpu->kvm, irq);
> +				/* try to update RVI */
> +				kvm_make_request(KVM_REQ_EVENT,
> vcpu);
> +			}
> +		}
> +
>  		WARN_ON(irq < 0);
>  		vmcs12->vm_exit_intr_info = irq |
>  			INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR;
> --
> 1.9.1
> 
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