Re: [PATCH 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0

[Like Xu]

cc Andi,

On 8/10/2021 5:57 pm, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> SDM section 18.2.3 mentioned that:
>
>    "IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow indicator(s) of
>     any general-purpose or fixed-function counters via a single WRMSR."
>
> It is R/W mentioned by SDM, we read this msr on bare-metal during perf testing,
> the value is always 0 for CLX/SKX boxes on hands. Let's fill get_msr
> MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 as hardware behavior.
>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
> Btw, xen also fills get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL 0.
>
>   arch/x86/kvm/vmx/pmu_intel.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 10cc4f65c4ef..47260a8563f9 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -365,7 +365,7 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		msr_info->data = pmu->global_ctrl;
>   		return 0;
>   	case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> -		msr_info->data = pmu->global_ovf_ctrl;
> +		msr_info->data = 0;

Tested-by: Like Xu <likexu@xxxxxxxxxxx>

Further, better to drop 'u64 global_ovf_ctrl' directly.

>   		return 0;
>   	default:
>   		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||