Re: [RFC PATCH 03/13] KVM: SVM: Detect X2APIC virtualization (x2AVIC) support

[Maxim Levitsky <mlevitsk@redhat.com>]

On Sun, 2022-02-20 at 20:19 -0600, Suravee Suthikulpanit wrote:
> Add CPUID check for the x2APIC virtualization (x2AVIC) feature.
> If available, the SVM driver can support both AVIC and x2AVIC modes
> when load the kvm_amd driver with avic=1. The operating mode will be
> determined at runtime depending on the guest APIC mode.
> 
> Also introduce a helper function to get the AVIC operating mode
> based on the VMCB configuration.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
>  arch/x86/include/asm/svm.h |  3 +++
>  arch/x86/kvm/svm/avic.c    | 44 ++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/svm/svm.c     |  8 ++-----
>  arch/x86/kvm/svm/svm.h     |  1 +
>  4 files changed, 50 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 7eb2df5417fb..7a7a2297165b 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -195,6 +195,9 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
>  #define AVIC_ENABLE_SHIFT 31
>  #define AVIC_ENABLE_MASK (1 << AVIC_ENABLE_SHIFT)
>  
> +#define X2APIC_MODE_SHIFT 30
> +#define X2APIC_MODE_MASK (1 << X2APIC_MODE_SHIFT)
> +
>  #define LBR_CTL_ENABLE_MASK BIT_ULL(0)
>  #define VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK BIT_ULL(1)
>  
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 472445aaaf42..abde08ca23ab 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -40,6 +40,15 @@
>  #define AVIC_GATAG_TO_VMID(x)		((x >> AVIC_VCPU_ID_BITS) & AVIC_VM_ID_MASK)
>  #define AVIC_GATAG_TO_VCPUID(x)		(x & AVIC_VCPU_ID_MASK)
>  
> +#define IS_AVIC_MODE_X1(x)		(avic_get_vcpu_apic_mode(x) == AVIC_MODE_X1)
> +#define IS_AVIC_MODE_X2(x)		(avic_get_vcpu_apic_mode(x) == AVIC_MODE_X2)
> +
> +enum avic_modes {
> +	AVIC_MODE_NONE = 0,
> +	AVIC_MODE_X1,
> +	AVIC_MODE_X2,
> +};
> +
>  /* Note:
>   * This hash table is used to map VM_ID to a struct kvm_svm,
>   * when handling AMD IOMMU GALOG notification to schedule in
> @@ -50,6 +59,7 @@ static DEFINE_HASHTABLE(svm_vm_data_hash, SVM_VM_DATA_HASH_BITS);
>  static u32 next_vm_id = 0;
>  static bool next_vm_id_wrapped = 0;
>  static DEFINE_SPINLOCK(svm_vm_data_hash_lock);
> +static enum avic_modes avic_mode;
>  
>  /*
>   * This is a wrapper of struct amd_iommu_ir_data.
> @@ -59,6 +69,15 @@ struct amd_svm_iommu_ir {
>  	void *data;		/* Storing pointer to struct amd_ir_data */
>  };
>  
> +static inline enum avic_modes avic_get_vcpu_apic_mode(struct vcpu_svm *svm)
> +{
> +	if (svm->vmcb->control.int_ctl & X2APIC_MODE_MASK)
> +		return AVIC_MODE_X2;
> +	else if (svm->vmcb->control.int_ctl & AVIC_ENABLE_MASK)
> +		return AVIC_MODE_X1;
> +	else
> +		return AVIC_MODE_NONE;
> +}
I a bit don't like it.

By definition if a vCPU has x2apic, it will use x2avic and if it is in 
xapic mode it will use plain avic, unless avic is inhibited,
which will also be the case when vCPU is in x2apic mode but hardware
doesn't support x2avic.

But I might have beeing mistaken here - anyway this function should
be added when it is used so it will be clear how and why it is needed.


>  
>  /* Note:
>   * This function is called from IOMMU driver to notify
> @@ -1016,3 +1035,28 @@ void avic_vcpu_unblocking(struct kvm_vcpu *vcpu)
>  
>  	put_cpu();
>  }
> +
> +/*
> + * Note:
> + * - The module param avic enable both xAPIC and x2APIC mode.
> + * - Hypervisor can support both xAVIC and x2AVIC in the same guest.
> + * - The mode can be switched at run-time.
> + */
> +bool avic_hardware_setup(struct kvm_x86_ops *x86_ops)
> +{
> +	if (!npt_enabled)
> +		return false;
> +
> +	if (boot_cpu_has(X86_FEATURE_AVIC)) {
> +		avic_mode = AVIC_MODE_X1;
> +		pr_info("AVIC enabled\n");
> +	}
> +
> +	if (boot_cpu_has(X86_FEATURE_X2AVIC)) {
> +		avic_mode = AVIC_MODE_X2;
> +		pr_info("x2AVIC enabled\n");
> +	}
> +
> +	amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
If AVIC is not enabled, I guess no need to register GA log notifier?

> +	return !!avic_mode;
> +}
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 821edf664e7a..3048f4b758d6 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4817,13 +4817,9 @@ static __init int svm_hardware_setup(void)
>  			nrips = false;
>  	}
>  
> -	enable_apicv = avic = avic && npt_enabled && boot_cpu_has(X86_FEATURE_AVIC);
> +	enable_apicv = avic = avic && avic_hardware_setup(&svm_x86_ops);
>  
> -	if (enable_apicv) {
> -		pr_info("AVIC enabled\n");
> -
> -		amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
> -	} else {
> +	if (!enable_apicv) {
>  		svm_x86_ops.vcpu_blocking = NULL;
>  		svm_x86_ops.vcpu_unblocking = NULL;
>  	}
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index fa98d6844728..b53c83a44ec2 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -558,6 +558,7 @@ extern struct kvm_x86_nested_ops svm_nested_ops;
>  
>  /* avic.c */
>  
> +bool avic_hardware_setup(struct kvm_x86_ops *ops);
>  int avic_ga_log_notifier(u32 ga_tag);
>  void avic_vm_destroy(struct kvm *kvm);
>  int avic_vm_init(struct kvm *kvm);


Best regards,
	Maxim Levitsky