Re: [PATCH v2 3/5] KVM: x86: Use common 'enable_apicv' variable for both APICv and AVIC

[Maxim Levitsky <mlevitsk@redhat.com>]

On Tue, 2021-05-18 at 16:43 +0200, Vitaly Kuznetsov wrote:
> Unify VMX and SVM code by moving APICv/AVIC enablement tracking to common
> 'enable_apicv' variable. Note: unlike APICv, AVIC is disabled by default.
> 
> No functional change intended.
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  1 +
>  arch/x86/kvm/svm/avic.c         | 14 +++++---------
>  arch/x86/kvm/svm/svm.c          | 23 ++++++++++++++---------
>  arch/x86/kvm/svm/svm.h          |  2 --
>  arch/x86/kvm/vmx/capabilities.h |  1 -
>  arch/x86/kvm/vmx/vmx.c          |  1 -
>  arch/x86/kvm/x86.c              |  3 +++
>  7 files changed, 23 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 55efbacfc244..a2197fcf0e7c 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1422,6 +1422,7 @@ struct kvm_arch_async_pf {
>  extern u32 __read_mostly kvm_nr_uret_msrs;
>  extern u64 __read_mostly host_efer;
>  extern bool __read_mostly allow_smaller_maxphyaddr;
> +extern bool __read_mostly enable_apicv;
>  extern struct kvm_x86_ops kvm_x86_ops;
>  
>  #define KVM_X86_OP(func) \
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 1c1bf911e02b..05cd0b128b02 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -27,10 +27,6 @@
>  #include "irq.h"
>  #include "svm.h"
>  
> -/* enable / disable AVIC */
> -int avic;
> -module_param(avic, int, S_IRUGO);
> -
>  #define SVM_AVIC_DOORBELL	0xc001011b
>  
>  #define AVIC_HPA_MASK	~((0xFFFULL << 52) | 0xFFF)
> @@ -124,7 +120,7 @@ void avic_vm_destroy(struct kvm *kvm)
>  	unsigned long flags;
>  	struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
>  
> -	if (!avic)
> +	if (!enable_apicv)
>  		return;
>  
>  	if (kvm_svm->avic_logical_id_table_page)
> @@ -147,7 +143,7 @@ int avic_vm_init(struct kvm *kvm)
>  	struct page *l_page;
>  	u32 vm_id;
>  
> -	if (!avic)
> +	if (!enable_apicv)
>  		return 0;
>  
>  	/* Allocating physical APIC ID table (4KB) */
> @@ -569,7 +565,7 @@ int avic_init_vcpu(struct vcpu_svm *svm)
>  	int ret;
>  	struct kvm_vcpu *vcpu = &svm->vcpu;
>  
> -	if (!avic || !irqchip_in_kernel(vcpu->kvm))
> +	if (!enable_apicv || !irqchip_in_kernel(vcpu->kvm))
>  		return 0;
>  
>  	ret = avic_init_backing_page(vcpu);
> @@ -593,7 +589,7 @@ void avic_post_state_restore(struct kvm_vcpu *vcpu)
>  
>  void svm_toggle_avic_for_irq_window(struct kvm_vcpu *vcpu, bool activate)
>  {
> -	if (!avic || !lapic_in_kernel(vcpu))
> +	if (!enable_apicv || !lapic_in_kernel(vcpu))
>  		return;
>  
>  	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
> @@ -653,7 +649,7 @@ void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
>  	struct vmcb *vmcb = svm->vmcb;
>  	bool activated = kvm_vcpu_apicv_active(vcpu);
>  
> -	if (!avic)
> +	if (!enable_apicv)
>  		return;
>  
>  	if (activated) {
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 8c3918a11826..0d6ec34d1e4b 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -185,6 +185,10 @@ module_param(vls, int, 0444);
>  static int vgif = true;
>  module_param(vgif, int, 0444);
>  
> +/* enable / disable AVIC */
> +static int avic;
> +module_param(avic, int, 0444);
> +
>  bool __read_mostly dump_invalid_vmcb;
>  module_param(dump_invalid_vmcb, bool, 0644);
>  
> @@ -1009,14 +1013,15 @@ static __init int svm_hardware_setup(void)
>  			nrips = false;
>  	}
>  
> -	if (avic) {
> -		if (!npt_enabled || !boot_cpu_has(X86_FEATURE_AVIC)) {
> -			avic = false;
> -		} else {
> -			pr_info("AVIC enabled\n");
> +	if (!npt_enabled || !boot_cpu_has(X86_FEATURE_AVIC))
> +		avic = false;
>  
> -			amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
> -		}
> +	/* 'enable_apicv' is common between VMX/SVM but the defaults differ */
> +	enable_apicv = avic;
> +	if (enable_apicv) {
> +		pr_info("AVIC enabled\n");
> +
> +		amd_iommu_register_ga_log_notifier(&avic_ga_log_notifier);
>  	}
>  
>  	if (vls) {
> @@ -4427,13 +4432,13 @@ static int svm_vm_init(struct kvm *kvm)
>  	if (!pause_filter_count || !pause_filter_thresh)
>  		kvm->arch.pause_in_guest = true;
>  
> -	if (avic) {
> +	if (enable_apicv) {
>  		int ret = avic_vm_init(kvm);
>  		if (ret)
>  			return ret;
>  	}
>  
> -	kvm_apicv_init(kvm, avic);
> +	kvm_apicv_init(kvm, enable_apicv);
>  	return 0;
>  }
>  
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index e44567ceb865..a514b490db4a 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -479,8 +479,6 @@ extern struct kvm_x86_nested_ops svm_nested_ops;
>  
>  #define VMCB_AVIC_APIC_BAR_MASK		0xFFFFFFFFFF000ULL
>  
> -extern int avic;
> -
>  static inline void avic_update_vapic_bar(struct vcpu_svm *svm, u64 data)
>  {
>  	svm->vmcb->control.avic_vapic_bar = data & VMCB_AVIC_APIC_BAR_MASK;
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index aa0e7872fcc9..4705ad55abb5 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -12,7 +12,6 @@ extern bool __read_mostly enable_ept;
>  extern bool __read_mostly enable_unrestricted_guest;
>  extern bool __read_mostly enable_ept_ad_bits;
>  extern bool __read_mostly enable_pml;
> -extern bool __read_mostly enable_apicv;
>  extern int __read_mostly pt_mode;
>  
>  #define PT_MODE_SYSTEM		0
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 4bceb5ca3a89..5e9ba10e9c2d 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -101,7 +101,6 @@ module_param(emulate_invalid_guest_state, bool, S_IRUGO);
>  static bool __read_mostly fasteoi = 1;
>  module_param(fasteoi, bool, S_IRUGO);
>  
> -bool __read_mostly enable_apicv = 1;
>  module_param(enable_apicv, bool, S_IRUGO);
>  
>  /*
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9b6bca616929..23fdbba6b394 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -209,6 +209,9 @@ EXPORT_SYMBOL_GPL(host_efer);
>  bool __read_mostly allow_smaller_maxphyaddr = 0;
>  EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
>  
> +bool __read_mostly enable_apicv = true;

Nitpick: I don't like this asymmetry.

VMX and the common code uses the enable_apicv module param and variable,
while SVM uses avic, which sets the enable_apicv variable.
 
I'll prefer both VMX and SVM have their own private variable
for their avic/apicv module param, 
which should set a common variable later.
 

Best regards,
	Maxim Levitsky


> +EXPORT_SYMBOL_GPL(enable_apicv);
> +
>  u64 __read_mostly host_xss;
>  EXPORT_SYMBOL_GPL(host_xss);
>  u64 __read_mostly supported_xss;