Re: [PATCH 1/2] KVM: x86: Deduplicate MSR interception enabling and disabling

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 6/12/2025 4:19 PM, Chao Gao wrote:
> Extract a common function from MSR interception disabling logic and create
> disabling and enabling functions based on it. This removes most of the
> duplicated code for MSR interception disabling/enabling.
>
> No functional change intended.
>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> ---
>  arch/x86/kvm/svm/svm.c | 23 +++++++++--------------
>  arch/x86/kvm/svm/svm.h | 10 +---------
>  arch/x86/kvm/vmx/vmx.c | 25 +++++++++----------------
>  arch/x86/kvm/vmx/vmx.h | 10 +---------
>  4 files changed, 20 insertions(+), 48 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 5453478d1ca3..cc5f81afd8af 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -685,21 +685,21 @@ static bool msr_write_intercepted(struct kvm_vcpu *vcpu, u32 msr)
>  	return svm_test_msr_bitmap_write(msrpm, msr);
>  }
>  
> -void svm_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
> +void svm_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type, bool enable)
>  {
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  	void *msrpm = svm->msrpm;
>  
>  	/* Don't disable interception for MSRs userspace wants to handle. */
>  	if (type & MSR_TYPE_R) {
> -		if (kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_READ))
> +		if (!enable && kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_READ))
>  			svm_clear_msr_bitmap_read(msrpm, msr);
>  		else
>  			svm_set_msr_bitmap_read(msrpm, msr);
>  	}
>  
>  	if (type & MSR_TYPE_W) {
> -		if (kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_WRITE))
> +		if (!enable && kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_WRITE))
>  			svm_clear_msr_bitmap_write(msrpm, msr);
>  		else
>  			svm_set_msr_bitmap_write(msrpm, msr);
> @@ -709,19 +709,14 @@ void svm_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
>  	svm->nested.force_msr_bitmap_recalc = true;
>  }
>  
> -void svm_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
> +void svm_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
>  {
> -	struct vcpu_svm *svm = to_svm(vcpu);
> -	void *msrpm = svm->msrpm;
> -
> -	if (type & MSR_TYPE_R)
> -		svm_set_msr_bitmap_read(msrpm, msr);
> -
> -	if (type & MSR_TYPE_W)
> -		svm_set_msr_bitmap_write(msrpm, msr);
> +	svm_set_intercept_for_msr(vcpu, msr, type, false);
> +}
>  
> -	svm_hv_vmcb_dirty_nested_enlightenments(vcpu);
> -	svm->nested.force_msr_bitmap_recalc = true;
> +void svm_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
> +{
> +	svm_set_intercept_for_msr(vcpu, msr, type, true);
>  }
>  
>  void *svm_alloc_permissions_map(unsigned long size, gfp_t gfp_mask)
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 8d3279563261..faa478d9fc62 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -696,15 +696,7 @@ void svm_complete_interrupt_delivery(struct kvm_vcpu *vcpu, int delivery_mode,
>  
>  void svm_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type);
>  void svm_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type);
> -
> -static inline void svm_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
> -					     int type, bool enable_intercept)
> -{
> -	if (enable_intercept)
> -		svm_enable_intercept_for_msr(vcpu, msr, type);
> -	else
> -		svm_disable_intercept_for_msr(vcpu, msr, type);
> -}
> +void svm_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type, bool enable);
>  
>  /* nested.c */
>  
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 277c6b5b5d5f..559261b18512 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3952,7 +3952,7 @@ static void vmx_msr_bitmap_l01_changed(struct vcpu_vmx *vmx)
>  	vmx->nested.force_msr_bitmap_recalc = true;
>  }
>  
> -void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
> +void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type, bool enable)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  	unsigned long *msr_bitmap = vmx->vmcs01.msr_bitmap;
> @@ -3963,35 +3963,28 @@ void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
>  	vmx_msr_bitmap_l01_changed(vmx);
>  
>  	if (type & MSR_TYPE_R) {
> -		if (kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_READ))
> +		if (!enable && kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_READ))
>  			vmx_clear_msr_bitmap_read(msr_bitmap, msr);
>  		else
>  			vmx_set_msr_bitmap_read(msr_bitmap, msr);
>  	}
>  
>  	if (type & MSR_TYPE_W) {
> -		if (kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_WRITE))
> +		if (!enable && kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_WRITE))
>  			vmx_clear_msr_bitmap_write(msr_bitmap, msr);
>  		else
>  			vmx_set_msr_bitmap_write(msr_bitmap, msr);
>  	}
>  }
>  
> -void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
> +void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
>  {
> -	struct vcpu_vmx *vmx = to_vmx(vcpu);
> -	unsigned long *msr_bitmap = vmx->vmcs01.msr_bitmap;
> -
> -	if (!cpu_has_vmx_msr_bitmap())
> -		return;
> -
> -	vmx_msr_bitmap_l01_changed(vmx);
> -
> -	if (type & MSR_TYPE_R)
> -		vmx_set_msr_bitmap_read(msr_bitmap, msr);
> +	vmx_set_intercept_for_msr(vcpu, msr, type, false);
> +}
>  
> -	if (type & MSR_TYPE_W)
> -		vmx_set_msr_bitmap_write(msr_bitmap, msr);
> +void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
> +{
> +	vmx_set_intercept_for_msr(vcpu, msr, type, true);
>  }
>  
>  static void vmx_update_msr_bitmap_x2apic(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index a26fe3d9e1d2..31acd8c726e3 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -388,21 +388,13 @@ void vmx_ept_load_pdptrs(struct kvm_vcpu *vcpu);
>  
>  void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type);
>  void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type);
> +void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type, bool enable);
>  
>  u64 vmx_get_l2_tsc_offset(struct kvm_vcpu *vcpu);
>  u64 vmx_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu);
>  
>  gva_t vmx_get_untagged_addr(struct kvm_vcpu *vcpu, gva_t gva, unsigned int flags);
>  
> -static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
> -					     int type, bool value)
> -{
> -	if (value)
> -		vmx_enable_intercept_for_msr(vcpu, msr, type);
> -	else
> -		vmx_disable_intercept_for_msr(vcpu, msr, type);
> -}
> -
>  void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu);
>  
>  /*

The change looks good to me. 

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>

Just curious, is there a preference on using these 3 interfaces? When
should we use the disable/enable interfaces? When should be we use the set
interface?  or no preference?