Re: [PATCH v11 08/16] KVM: x86/pmu: Refactor code to support guest Arch LBR

["Liang, Kan" <kan.liang@linux.intel.com>]

On 5/5/2022 11:32 PM, Yang Weijiang wrote:
> Take account of Arch LBR when do sanity checks before program
> vPMU for guest. Pass through Arch LBR recording MSRs to guest
> to gain better performance. Note, Arch LBR and Legacy LBR support
> are mutually exclusive, i.e., they're not both available on one
> platform.
> 
> Co-developed-by: Like Xu <like.xu@linux.intel.com>
> Signed-off-by: Like Xu <like.xu@linux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>   arch/x86/kvm/vmx/pmu_intel.c | 40 ++++++++++++++++++++++++++++--------
>   arch/x86/kvm/vmx/vmx.c       |  3 +++
>   2 files changed, 35 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index aa36d2072b91..bd4ddf63ba8f 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -170,12 +170,16 @@ static inline struct kvm_pmc *get_fw_gp_pmc(struct kvm_pmu *pmu, u32 msr)
>   
>   bool intel_pmu_lbr_is_compatible(struct kvm_vcpu *vcpu)
>   {
> +	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR))
> +		return guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR);
> +
>   	/*
>   	 * As a first step, a guest could only enable LBR feature if its
>   	 * cpu model is the same as the host because the LBR registers
>   	 * would be pass-through to the guest and they're model specific.
>   	 */
> -	return boot_cpu_data.x86_model == guest_cpuid_model(vcpu);
> +	return !boot_cpu_has(X86_FEATURE_ARCH_LBR) &&
> +		boot_cpu_data.x86_model == guest_cpuid_model(vcpu);
>   }
>   
>   bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu)
> @@ -199,12 +203,20 @@ static bool intel_pmu_is_valid_lbr_msr(struct kvm_vcpu *vcpu, u32 index)
>   		return ret;
>   	}
>   
> -	ret = (index == MSR_LBR_SELECT) || (index == MSR_LBR_TOS) ||
> -		(index >= records->from && index < records->from + records->nr) ||
> -		(index >= records->to && index < records->to + records->nr);
> +	if (!guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR))
> +		ret = (index == MSR_LBR_SELECT) || (index == MSR_LBR_TOS);
> +

Shouldn't we return immediately if (ret == true)?
Keep checking if (!ret) looks uncommon.

Actually we probably don't need the ret in this function.

	if (!guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR) &&
	    ((index == MSR_LBR_SELECT) || (index == MSR_LBR_TOS)))
		return true;

> +	if (!ret) {
> +		ret = (index >= records->from &&
> +		       index < records->from + records->nr) ||
> +		      (index >= records->to &&
> +		       index < records->to + records->nr);
> +	}

	if ((index >= records->from &&
	    index < records->from + records->nr) ||
	    (index >= records->to &&
	    index < records->to + records->nr))
		return true;

>   
> -	if (!ret && records->info)
> -		ret = (index >= records->info && index < records->info + records->nr);
> +	if (!ret && records->info) {
> +		ret = (index >= records->info &&
> +		       index < records->info + records->nr);
> +	}

	if (records->info &&
	    (index >= records->info && index < records->info + records->nr)
		return true;

	return false;

Sorry, I didn't notice it in the previous review.

Thanks,
Kan

>   
>   	return ret;
>   }
> @@ -742,6 +754,9 @@ static void vmx_update_intercept_for_lbr_msrs(struct kvm_vcpu *vcpu, bool set)
>   			vmx_set_intercept_for_msr(vcpu, lbr->info + i, MSR_TYPE_RW, set);
>   	}
>   
> +	if (guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR))
> +		return;
> +
>   	vmx_set_intercept_for_msr(vcpu, MSR_LBR_SELECT, MSR_TYPE_RW, set);
>   	vmx_set_intercept_for_msr(vcpu, MSR_LBR_TOS, MSR_TYPE_RW, set);
>   }
> @@ -782,10 +797,13 @@ void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>   	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
> +	bool lbr_enable = guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR) ?
> +		(vmcs_read64(GUEST_IA32_LBR_CTL) & ARCH_LBR_CTL_LBREN) :
> +		(vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR);
>   
>   	if (!lbr_desc->event) {
>   		vmx_disable_lbr_msrs_passthrough(vcpu);
> -		if (vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR)
> +		if (lbr_enable)
>   			goto warn;
>   		if (test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use))
>   			goto warn;
> @@ -802,13 +820,19 @@ void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu)
>   	return;
>   
>   warn:
> +	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR))
> +		wrmsrl(MSR_ARCH_LBR_DEPTH, lbr_desc->records.nr);
>   	pr_warn_ratelimited("kvm: vcpu-%d: fail to passthrough LBR.\n",
>   		vcpu->vcpu_id);
>   }
>   
>   static void intel_pmu_cleanup(struct kvm_vcpu *vcpu)
>   {
> -	if (!(vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR))
> +	bool lbr_enable = guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR) ?
> +		(vmcs_read64(GUEST_IA32_LBR_CTL) & ARCH_LBR_CTL_LBREN) :
> +		(vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR);
> +
> +	if (!lbr_enable)
>   		intel_pmu_release_guest_lbr_event(vcpu);
>   }
>   
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b6bc7d97e4b4..98e56a909c01 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -573,6 +573,9 @@ static bool is_valid_passthrough_msr(u32 msr)
>   	case MSR_LBR_NHM_TO ... MSR_LBR_NHM_TO + 31:
>   	case MSR_LBR_CORE_FROM ... MSR_LBR_CORE_FROM + 8:
>   	case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 8:
> +	case MSR_ARCH_LBR_FROM_0 ... MSR_ARCH_LBR_FROM_0 + 31:
> +	case MSR_ARCH_LBR_TO_0 ... MSR_ARCH_LBR_TO_0 + 31:
> +	case MSR_ARCH_LBR_INFO_0 ... MSR_ARCH_LBR_INFO_0 + 31:
>   		/* LBR MSRs. These are handled in vmx_update_intercept_for_lbr_msrs() */
>   		return true;
>   	}