Re: [PATCH v2 06/15] KVM: vmx/pmu: Emulate MSR_ARCH_LBR_CTL for guest Arch LBR

[Like Xu]

On 25/11/2022 12:05 pm, Yang Weijiang wrote:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index cea8c07f5229..1ae2efc29546 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2120,6 +2120,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   						VM_EXIT_SAVE_DEBUG_CONTROLS)
>   			get_vmcs12(vcpu)->guest_ia32_debugctl = data;
>   
> +		/*
> +		 * For Arch LBR, IA32_DEBUGCTL[bit 0] has no meaning.
> +		 * It can be written to 0 or 1, but reads will always return 0.
> +		 */

The comment looks good, please verify it with a test.

> +		if (guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR))
> +			data &= ~DEBUGCTLMSR_LBR;
> +
>   		vmcs_write64(GUEST_IA32_DEBUGCTL, data);
>   		if (intel_pmu_lbr_is_enabled(vcpu) && !to_vmx(vcpu)->lbr_desc.event &&
>   		    (data & DEBUGCTLMSR_LBR))