Re: [PATCH v2 11/11] KVM: nSVM: implement support for nested VNMI

[Santosh Shukla]

On 11/30/2022 1:07 AM, Maxim Levitsky wrote:
> This patch allows L1 to use vNMI to accelerate its injection
> of NMIs to L2 by passing through vNMI int_ctl bits from vmcb12
> to/from vmcb02.
> 
> While L2 runs, L1's vNMI is inhibited, and L1's NMIs are injected
> normally.
> 
> In order to support nested VNMI requires saving and restoring the VNMI
> bits during nested entry and exit.
> In case of L1 and L2 both using VNMI- Copy VNMI bits from vmcb12 to
> vmcb02 during entry and vice-versa during exit.
> And in case of L1 uses VNMI and L2 doesn't- Copy VNMI bits from vmcb01 to
> vmcb02 during entry and vice-versa during exit.
> 
> Tested with the KVM-unit-test and Nested Guest scenario.
> 
> 
> Signed-off-by: Santosh Shukla <santosh.shukla@xxxxxxx>
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> ---
>  arch/x86/kvm/svm/nested.c | 13 ++++++++++++-
>  arch/x86/kvm/svm/svm.c    |  5 +++++
>  arch/x86/kvm/svm/svm.h    |  6 ++++++
>  3 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 5bea672bf8b12d..81346665058e26 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -278,6 +278,11 @@ static bool __nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
>  	if (CC(!nested_svm_check_tlb_ctl(vcpu, control->tlb_ctl)))
>  		return false;
>  
> +	if (CC((control->int_ctl & V_NMI_ENABLE) &&
> +		!vmcb12_is_intercept(control, INTERCEPT_NMI))) {
> +		return false;
> +	}
> +
>  	return true;
>  }
>  
> @@ -427,6 +432,9 @@ void nested_sync_control_from_vmcb02(struct vcpu_svm *svm)
>  	if (nested_vgif_enabled(svm))
>  		mask |= V_GIF_MASK;
>  
> +	if (nested_vnmi_enabled(svm))
> +		mask |= V_NMI_MASK | V_NMI_PENDING;
> +
>  	svm->nested.ctl.int_ctl        &= ~mask;
>  	svm->nested.ctl.int_ctl        |= svm->vmcb->control.int_ctl & mask;
>  }
> @@ -682,8 +690,11 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
>  	else
>  		int_ctl_vmcb01_bits |= (V_GIF_MASK | V_GIF_ENABLE_MASK);
>  
> -	if (vnmi)
> +	if (vnmi) {

To avoid above change, I think we should move nested bits from 10/11 to this i.e.. move function
(nested_svm_save_vnmi and nested_svm_restore_vnmi) to this patch.

make sense?

Thanks,
Santosh

>  		nested_svm_save_vnmi(svm);
> +		if (nested_vnmi_enabled(svm))
> +			int_ctl_vmcb12_bits |= (V_NMI_PENDING | V_NMI_ENABLE | V_NMI_MASK);
> +	}
>  
>  	/* Copied from vmcb01.  msrpm_base can be overwritten later.  */
>  	vmcb02->control.nested_ctl = vmcb01->control.nested_ctl;
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index bf10adcf3170a8..fb203f536d2f9b 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4214,6 +4214,8 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>  
>  	svm->vgif_enabled = vgif && guest_cpuid_has(vcpu, X86_FEATURE_VGIF);
>  
> +	svm->vnmi_enabled = vnmi && guest_cpuid_has(vcpu, X86_FEATURE_AMD_VNMI);
> +
>  	svm_recalc_instruction_intercepts(vcpu, svm);
>  
>  	/* For sev guests, the memory encryption bit is not reserved in CR3.  */
> @@ -4967,6 +4969,9 @@ static __init void svm_set_cpu_caps(void)
>  		if (vgif)
>  			kvm_cpu_cap_set(X86_FEATURE_VGIF);
>  
> +		if (vnmi)
> +			kvm_cpu_cap_set(X86_FEATURE_AMD_VNMI);
> +
>  		/* Nested VM can receive #VMEXIT instead of triggering #GP */
>  		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);
>  	}
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 0b7e1790fadde1..8fb2085188c5ac 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -271,6 +271,7 @@ struct vcpu_svm {
>  	bool pause_filter_enabled         : 1;
>  	bool pause_threshold_enabled      : 1;
>  	bool vgif_enabled                 : 1;
> +	bool vnmi_enabled                 : 1;
>  
>  	u32 ldr_reg;
>  	u32 dfr_reg;
> @@ -545,6 +546,11 @@ static inline bool nested_npt_enabled(struct vcpu_svm *svm)
>  	return svm->nested.ctl.nested_ctl & SVM_NESTED_CTL_NP_ENABLE;
>  }
>  
> +static inline bool nested_vnmi_enabled(struct vcpu_svm *svm)
> +{
> +	return svm->vnmi_enabled && (svm->nested.ctl.int_ctl & V_NMI_ENABLE);
> +}
> +
>  static inline bool is_x2apic_msrpm_offset(u32 offset)
>  {
>  	/* 4 msrs per u8, and 4 u8 in u32 */