linux-kernel - Re: [RFC PATCH 04/13] KVM: SVM: Only call vcpu

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Date:   Thu, 24 Feb 2022 18:54:58 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, seanjc@...gle.com, joro@...tes.org,
        jon.grimm@....com, wei.huang2@....com, terry.bowman@....com
Subject: Re: [RFC PATCH 04/13] KVM: SVM: Only call vcpu_(un)blocking when
 AVIC is enabled.

On Sun, 2022-02-20 at 20:19 -0600, Suravee Suthikulpanit wrote:
> The kvm_x86_ops.vcpu_(un)blocking are needed by AVIC only.
> Therefore, set the ops only when AVIC is enabled.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  arch/x86/kvm/svm/avic.c | 12 ++++++++++--
>  arch/x86/kvm/svm/svm.c  |  7 -------
>  arch/x86/kvm/svm/svm.h  |  2 --
>  3 files changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index abde08ca23ab..0040824e4376 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -996,7 +996,7 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu)
>  	WRITE_ONCE(*(svm->avic_physical_id_cache), entry);
>  }
>  
> -void avic_vcpu_blocking(struct kvm_vcpu *vcpu)
> +static void avic_vcpu_blocking(struct kvm_vcpu *vcpu)
>  {
>  	if (!kvm_vcpu_apicv_active(vcpu))
>  		return;
> @@ -1021,7 +1021,7 @@ void avic_vcpu_blocking(struct kvm_vcpu *vcpu)
>  	preempt_enable();
>  }
>  
> -void avic_vcpu_unblocking(struct kvm_vcpu *vcpu)
> +static void avic_vcpu_unblocking(struct kvm_vcpu *vcpu)
>  {
>  	int cpu;
>  
> @@ -1057,6 +1057,14 @@ bool avic_hardware_setup(struct kvm_x86_ops *x86_ops)
>  		pr_info("x2AVIC enabled\n");
>  	}
>  
> +	if (avic_mode) {
> +		x86_ops->vcpu_blocking = avic_vcpu_blocking;
> +		x86_ops->vcpu_unblocking = avic_vcpu_unblocking;
> +	} else {
> +		x86_ops->vcpu_blocking = NULL;
> +		x86_ops->vcpu_unblocking = NULL;
> +	}
> +
>  	amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
>  	return !!avic_mode;
>  }
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 3048f4b758d6..3687026f2859 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4531,8 +4531,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
>  	.prepare_guest_switch = svm_prepare_guest_switch,
>  	.vcpu_load = svm_vcpu_load,
>  	.vcpu_put = svm_vcpu_put,
> -	.vcpu_blocking = avic_vcpu_blocking,
> -	.vcpu_unblocking = avic_vcpu_unblocking,
>  
>  	.update_exception_bitmap = svm_update_exception_bitmap,
>  	.get_msr_feature = svm_get_msr_feature,
> @@ -4819,11 +4817,6 @@ static __init int svm_hardware_setup(void)
>  
>  	enable_apicv = avic = avic && avic_hardware_setup(&svm_x86_ops);
>  
> -	if (!enable_apicv) {
> -		svm_x86_ops.vcpu_blocking = NULL;
> -		svm_x86_ops.vcpu_unblocking = NULL;
> -	}

Isn't this code already zeros these callbacks when avic is not enabled?

I am not sure why this patch is needed to be honest.

Best regards,
	Maxim Levitsky

> -
>  	if (vls) {
>  		if (!npt_enabled ||
>  		    !boot_cpu_has(X86_FEATURE_V_VMSAVE_VMLOAD) ||
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index b53c83a44ec2..1a0bf6b853df 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -578,8 +578,6 @@ void svm_hwapic_isr_update(struct kvm_vcpu *vcpu, int max_isr);
>  bool svm_dy_apicv_has_pending_interrupt(struct kvm_vcpu *vcpu);
>  int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
>  		       uint32_t guest_irq, bool set);
> -void avic_vcpu_blocking(struct kvm_vcpu *vcpu);
> -void avic_vcpu_unblocking(struct kvm_vcpu *vcpu);
>  void avic_ring_doorbell(struct kvm_vcpu *vcpu);
>  
>  /* sev.c */