linux-kernel - Re: [PART1 RFC v3 11/12] svm: Do not intercept CR8 when enable AVIC

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Date:	Fri, 18 Mar 2016 22:10:49 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:	pbonzini@...hat.com, joro@...tes.org, bp@...en8.de,
	gleb@...nel.org, alex.williamson@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, wei@...hat.com,
	sherry.hurwitz@....com
Subject: Re: [PART1 RFC v3 11/12] svm: Do not intercept CR8 when enable AVIC

2016-03-18 01:09-0500, Suravee Suthikulpanit:
> When enable AVIC:
>     * Do not intercept CR8 since this should be handled by AVIC HW.
>     * Also update TPR in APIC backing page when syncing CR8 before VMRUN
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  arch/x86/kvm/svm.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index ba84d57..d5418c3 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -984,6 +984,8 @@ static __init int svm_hardware_setup(void)
>  
>  	if (avic) {
>  		printk(KERN_INFO "kvm: AVIC enabled\n");
> +
> +		svm_x86_ops.update_cr8_intercept = NULL;

This doesn't look right.

>  	} else {
>  		svm_x86_ops.deliver_posted_interrupt = NULL;
>  	}
> @@ -1097,7 +1099,8 @@ static void init_vmcb(struct vcpu_svm *svm)
>  	set_cr_intercept(svm, INTERCEPT_CR0_WRITE);
>  	set_cr_intercept(svm, INTERCEPT_CR3_WRITE);
>  	set_cr_intercept(svm, INTERCEPT_CR4_WRITE);
> -	set_cr_intercept(svm, INTERCEPT_CR8_WRITE);
> +	if (!svm_vcpu_avic_enabled(svm))
> +		set_cr_intercept(svm, INTERCEPT_CR8_WRITE);
>  
>  	set_dr_intercepts(svm);
>  
> @@ -4080,7 +4083,8 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
>  {
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  
> -	if (is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK))
> +	if ((is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK)) ||
> +	     svm_vcpu_avic_enabled(svm))
>  		return;
>  
>  	clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
> @@ -4271,9 +4275,12 @@ static inline void sync_lapic_to_cr8(struct kvm_vcpu *vcpu)
>  	if (is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK))
>  		return;

I think we can exit early with svm_vcpu_avic_enabled().

>  
> -	cr8 = kvm_get_cr8(vcpu);
> +	cr8 = kvm_get_cr8(vcpu) & V_TPR_MASK;
>  	svm->vmcb->control.int_ctl &= ~V_TPR_MASK;
> -	svm->vmcb->control.int_ctl |= cr8 & V_TPR_MASK;
> +	svm->vmcb->control.int_ctl |= cr8;
> +
> +	if (svm_vcpu_avic_enabled(svm))
> +		kvm_lapic_set_reg(svm->vcpu.arch.apic, APIC_TASKPRI, (u32)cr8 << 4);

kvm_get_cr8() == kvm_lapic_get_reg(APIC_TASKPRI) >> 4.

>  }
>  
>  static void svm_complete_interrupts(struct vcpu_svm *svm)
> -- 
> 1.9.1
>