linux-kernel - Re: [PART1 RFC 8/9] svm: Do not intercept CR8 when enable AVIC

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Message-ID: <56BDFEBD.5080806@redhat.com>
Date:	Fri, 12 Feb 2016 16:48:13 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	joro@...tes.org, alex.williamson@...hat.com, gleb@...nel.org
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, wei@...hat.com,
	sherry.hurwitz@....com
Subject: Re: [PART1 RFC 8/9] svm: Do not intercept CR8 when enable AVIC



On 12/02/2016 14:59, Suravee Suthikulpanit wrote:
> From: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> 
> 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>

Note that latest KVM has a mechanism to disable APIC virtualization on a
per-CPU basis (kvm-vcpu_deactivate_apicv).  You need to implement this too.

Paolo

> ---
>  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 0998e67..32da657 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -981,6 +981,9 @@ static __init int svm_hardware_setup(void)
>  
>  	if (avic) {
>  		printk(KERN_INFO "kvm: AVIC enabled\n");
> +
> +		/* Do not do cr8 intercept if AVIC is enabled. */
> +		svm_x86_ops.update_cr8_intercept = NULL;
>  	} else {
>  		svm_x86_ops.deliver_posted_interrupt = NULL;
>  		svm_x86_ops.apicv_intr_pending = NULL;
> @@ -1098,7 +1101,8 @@ 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 (!avic)
> +		set_cr_intercept(svm, INTERCEPT_CR8_WRITE);
>  
>  	set_dr_intercepts(svm);
>  
> @@ -4248,7 +4252,8 @@ 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)) ||
> +	     avic)
>  		return;
>  
>  	clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
> @@ -4440,8 +4445,10 @@ static inline void sync_lapic_to_cr8(struct kvm_vcpu *vcpu)
>  	if (is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK))
>  		return;
>  
> -	cr8 = kvm_get_cr8(vcpu);
> -	svm->vmcb->control.v_tpr = cr8 & V_TPR_MASK;
> +	svm->vmcb->control.v_tpr = cr8 = kvm_get_cr8(vcpu) & V_TPR_MASK;
> +
> +	if (avic)
> +		*(avic_get_bk_page_entry(svm, APIC_TASKPRI)) = (u32)cr8 << 4;
>  }
>  
>  static void svm_complete_interrupts(struct vcpu_svm *svm)
>