linux-kernel - Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry

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Date:   Thu, 3 Nov 2016 17:00:43 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        yang.zhang.wz@...il.com, feng.wu@...el.com, mst@...hat.com
Subject: Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry



On 03/11/2016 16:03, Radim Krčmář wrote:
> 2016-11-03 14:30+0100, Paolo Bonzini:
>> On 26/10/2016 21:59, Radim Krčmář wrote:
>>> 2016-10-14 20:21+0200, Paolo Bonzini:
>>>> Calling apic_find_highest_irr results in IRR being scanned twice,
>>>> once in vmx_sync_pir_from_irr and once in apic_search_irr.  Change
>>>> sync_pir_from_irr to do the RVI write and kvm_apic_update_irr to
>>>> compute the new RVI on the fly.
>>>>
>>>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>>>> ---
>>>
>>> Reviewed-by: Radim Krčmář <rkrcmar@...hat.com>
>>
>> Nope, this breaks nested VMX exit on external interrupt.  For now I'm
>> testing only patch 1 and will push that one only to kvm/next.
> 
> Hm, does it also happen with this change?

Probably not but I wanted to understand why. :)

Paolo

> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4b20f7304b9c..6be110e53e9e 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -941,7 +941,7 @@ struct kvm_x86_ops {
>  	void (*set_virtual_x2apic_mode)(struct kvm_vcpu *vcpu, bool set);
>  	void (*set_apic_access_page_addr)(struct kvm_vcpu *vcpu, hpa_t hpa);
>  	void (*deliver_posted_interrupt)(struct kvm_vcpu *vcpu, int vector);
> -	void (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
> +	int (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
>  	int (*set_tss_addr)(struct kvm *kvm, unsigned int addr);
>  	int (*get_tdp_level)(void);
>  	u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index f8157a36ab09..ffa541d38343 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -4383,9 +4383,9 @@ static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
>  	return;
>  }
>  
> -static void svm_sync_pir_to_irr(struct kvm_vcpu *vcpu)
> +static int svm_sync_pir_to_irr(struct kvm_vcpu *vcpu)
>  {
> -	return;
> +	return -1; // XXX
>  }
>  
>  static void svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index f272ccfddc48..2211e1774733 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8493,17 +8493,15 @@ static void vmx_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr)
>  	}
>  }
>  
> -static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
> +static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> -	int max_irr;
>  
>  	if (!pi_test_on(&vmx->pi_desc))
>  		return;
>  
>  	pi_clear_on(&vmx->pi_desc);
> -	max_irr = kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
> -	vmx_hwapic_irr_update(vcpu, max_irr);
> +	return kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
>  }
>  
>  static void vmx_apicv_post_state_restore(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 20d572c18293..e8789f3a9bfd 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6675,7 +6675,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  		 * notified with kvm_vcpu_kick.
>  		 */
>  		if (vcpu->arch.apicv_active)
> -			kvm_x86_ops->sync_pir_to_irr(vcpu);
> +			kvm_x86_ops->hwapic_irr_update(vcpu, kvm_x86_ops->sync_pir_to_irr(vcpu));
>  	}
>  
>  	if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
>