Re: [PATCH v2 04/16] KVM: x86/pmu: Gate BUFFER_OVF reserved bit on guest DS

[Mi, Dapeng]

Reviewed-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>

On 8/28/2026 6:37 AM, Zide Chen wrote:
> global_status_rsvd unconditionally clears GLOBAL_STATUS_BUFFER_OVF
> (bit 62), even when the guest does not have X86_FEATURE_DS feature.
> Clear it only when guest_cpu_cap_has(vcpu, X86_FEATURE_DS), matching
> hardware behavior.
>
> Fixes: f5132b01386b ("KVM: Expose a version 2 architectural PMU to a guests")
> Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
> ---
> v2: new patch.
> ---
>  arch/x86/kvm/vmx/pmu_intel.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 11c9161dc853..9fdae437e569 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -576,8 +576,16 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>  			 ((BIT_ULL(pmu->nr_arch_fixed_counters) - 1) << KVM_FIXED_PMC_BASE_IDX));
>  	pmu->global_ctrl_rsvd = counter_rsvd;
>  
> -	pmu->global_status_rsvd = pmu->global_ctrl_rsvd
> -			& ~(GLOBAL_STATUS_BUFFER_OVF | GLOBAL_STATUS_COND_CHG);
> +	/*
> +	 * Layout of bits 48:0 in IA32_PERF_GLOBAL_CTRL is identical to
> +	 * IA32_PERF_GLOBAL_STATUS, but IA32_PERF_GLOBAL_STATUS has additional
> +	 * bits.
> +	 */
> +	pmu->global_status_rsvd = pmu->global_ctrl_rsvd;
> +	if (guest_cpu_cap_has(vcpu, X86_FEATURE_DS))
> +		pmu->global_status_rsvd &= ~GLOBAL_STATUS_BUFFER_OVF;
> +	pmu->global_status_rsvd &= ~GLOBAL_STATUS_COND_CHG;
> +
>  	if (vmx_pt_mode_is_host_guest())
>  		pmu->global_status_rsvd &= ~GLOBAL_STATUS_TRACE_TOPAPMI;
>