linux-kernel - Re: [RFCv2 PATCH 10/12] KVM: SVM: Introduce helper functions to (de)activate AVIC and x2AVIC

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Date:   Thu, 24 Mar 2022 17:40:24 +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,
        kernel test robot <lkp@...el.com>
Subject: Re: [RFCv2 PATCH 10/12] KVM: SVM: Introduce helper functions to
 (de)activate AVIC and x2AVIC

On Tue, 2022-03-08 at 10:39 -0600, Suravee Suthikulpanit wrote:
> Refactor the current logic for (de)activate AVIC into helper functions,
> and also add logic for (de)activate x2AVIC. The helper function are used
> when initializing AVIC and switching from AVIC to x2AVIC mode
> (handled by svm_refresh_spicv_exec_ctrl()).
> 
> When an AVIC-enabled guest switches from APIC to x2APIC mode during
> runtime, the SVM driver needs to perform the following steps:
> 
> 1. Set the x2APIC mode bit for AVIC in VMCB along with the maximum
> APIC ID support for each mode accodingly.
> 
> 2. Disable x2APIC MSRs interception in order to allow the hardware
> to virtualize x2APIC MSRs accesses.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  arch/x86/include/asm/svm.h |  1 +
>  arch/x86/kvm/svm/avic.c    | 48 ++++++++++++++++++++++++++++++++++----
>  2 files changed, 44 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 681a348a9365..f5337022104d 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -248,6 +248,7 @@ enum avic_ipi_failure_cause {
>  	AVIC_IPI_FAILURE_INVALID_BACKING_PAGE,
>  };
>  
> +#define AVIC_PHYSICAL_MAX_INDEX_MASK	GENMASK_ULL(9, 0)
>  
>  /*
>   * For AVIC, the max index allowed for physical APIC ID
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 53559b8dfa52..b8d6bf6b6ed5 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -66,6 +66,45 @@ struct amd_svm_iommu_ir {
>  	void *data;		/* Storing pointer to struct amd_ir_data */
>  };
>  
> +static inline void avic_set_x2apic_msr_interception(struct vcpu_svm *svm, bool disable)
> +{
> +	int i;
> +
> +	for (i = 0x800; i <= 0x8ff; i++)
> +		set_msr_interception(&svm->vcpu, svm->msrpm, i,
> +				     !disable, !disable);
> +}
> +
> +static void avic_activate_vmcb(struct vcpu_svm *svm)
> +{
> +	struct vmcb *vmcb = svm->vmcb01.ptr;
> +
> +	vmcb->control.int_ctl &= ~(AVIC_ENABLE_MASK | X2APIC_MODE_MASK);
> +	vmcb->control.avic_physical_id &= ~AVIC_PHYSICAL_MAX_INDEX_MASK;

This looks a bit better, I don't 100% like this but let it be.

Honestly I will eventualy add code to calculate and update this maximum
dynamically to avoid wasting microcode going over the whole table,
or worse having nested avic code doing so.


> +
> +	vmcb->control.int_ctl |= AVIC_ENABLE_MASK;
> +	if (apic_x2apic_mode(svm->vcpu.arch.apic)) {
> +		vmcb->control.int_ctl |= X2APIC_MODE_MASK;
> +		vmcb->control.avic_physical_id |= X2AVIC_MAX_PHYSICAL_ID;
> +		/* Disabling MSR intercept for x2APIC registers */
> +		avic_set_x2apic_msr_interception(svm, false);
> +	} else {
> +		vmcb->control.avic_physical_id |= AVIC_MAX_PHYSICAL_ID;
> +		/* Enabling MSR intercept for x2APIC registers */
> +		avic_set_x2apic_msr_interception(svm, true);
> +	}
> +}

> +
> +static void avic_deactivate_vmcb(struct vcpu_svm *svm)
> +{
> +	struct vmcb *vmcb = svm->vmcb01.ptr;
> +
> +	vmcb->control.int_ctl &= ~(AVIC_ENABLE_MASK | X2APIC_MODE_MASK);
> +	vmcb->control.avic_physical_id &= ~AVIC_PHYSICAL_MAX_INDEX_MASK;
> +
> +	/* Enabling MSR intercept for x2APIC registers */
> +	avic_set_x2apic_msr_interception(svm, true);
> +}
Makes sense.


>  
>  /* Note:
>   * This function is called from IOMMU driver to notify
> @@ -183,13 +222,12 @@ void avic_init_vmcb(struct vcpu_svm *svm)
>  	vmcb->control.avic_backing_page = bpa & AVIC_HPA_MASK;
>  	vmcb->control.avic_logical_id = lpa & AVIC_HPA_MASK;
>  	vmcb->control.avic_physical_id = ppa & AVIC_HPA_MASK;
> -	vmcb->control.avic_physical_id |= AVIC_MAX_PHYSICAL_ID;
>  	vmcb->control.avic_vapic_bar = APIC_DEFAULT_PHYS_BASE & VMCB_AVIC_APIC_BAR_MASK;
>  
>  	if (kvm_apicv_activated(svm->vcpu.kvm))
> -		vmcb->control.int_ctl |= AVIC_ENABLE_MASK;
> +		avic_activate_vmcb(svm);
>  	else
> -		vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
> +		avic_deactivate_vmcb(svm);
>  }
>  
>  static u64 *avic_get_physical_id_entry(struct kvm_vcpu *vcpu,
> @@ -703,9 +741,9 @@ void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
>  		 * accordingly before re-activating.
>  		 */
>  		avic_post_state_restore(vcpu);
> -		vmcb->control.int_ctl |= AVIC_ENABLE_MASK;
> +		avic_activate_vmcb(svm);
>  	} else {
> -		vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
> +		avic_deactivate_vmcb(svm);
>  	}
>  	vmcb_mark_dirty(vmcb, VMCB_AVIC);
>  


Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky