Re: [PATCH v3 08/18] KVM: x86/pmu: Switch to bitmask-based KVM PMU capabilities

[Yosry Ahmed]

> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index adafd6fa2c54..3310c370c5fa 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -1535,10 +1535,18 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		}
>  
>  		eax.split.version_id = kvm_pmu_cap.version;
> -		eax.split.num_counters = kvm_pmu_cap.num_counters_gp;
> +
> +		/* Contiguous GP counters only. */
> +		eax.split.num_counters =
> +			find_first_zero_bit(kvm_pmu_cap.cntr_mask,
> +					    KVM_MAX_NR_GP_COUNTERS);
>  		eax.split.bit_width = kvm_pmu_cap.bit_width_gp;
>  		eax.split.mask_length = kvm_pmu_cap.events_mask_len;
> -		edx.split.num_counters_fixed = kvm_pmu_cap.num_counters_fixed;
> +
> +		/* Contiguous fixed counters only. */
> +		edx.split.num_counters_fixed =
> +			find_first_zero_bit(kvm_pmu_cap.fixed_cntr_mask,
> +					    KVM_MAX_NR_FIXED_COUNTERS);
>  		edx.split.bit_width_fixed = kvm_pmu_cap.bit_width_fixed;
>  
>  		if (kvm_pmu_cap.version)
> @@ -1903,7 +1911,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  
>  		cpuid_entry_override(entry, CPUID_8000_0022_EAX);
>  
> -		ebx.split.num_core_pmc = kvm_pmu_cap.num_counters_gp;
> +		ebx.split.num_core_pmc = hweight64(kvm_pmu_cap.cntr_mask64);

Should this be the number of contiguous counters?

>  		entry->ebx = ebx.full;
>  		break;
>  	}
[..]  
> @@ -516,7 +517,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>  	union cpuid10_edx edx;
>  	u64 perf_capabilities;
>  	u64 fixed_mask;
> -	int nr_gp_counters;
> +	int nr_gp_counters, nr_fixed_counters;
>  	u64 counter_rsvd;
>  
>  	if (!lbr_desc)
> @@ -550,16 +551,25 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>  				      kvm_pmu_cap.events_mask_len);
>  	pmu->available_event_types = ~entry->ebx & (BIT_ULL(eax.split.mask_length) - 1);
>  
> -	fixed_mask = BIT_ULL(edx.split.num_counters_fixed) - 1;
> -	fixed_mask &= BIT_ULL(kvm_pmu_cap.num_counters_fixed) - 1;
> +	/*
> +	 * CPUID.0AH:EDX[4:0] can only enumerate contiguous counters. Clamp the
> +	 * value to the number of contiguous fixed counters supported by KVM.
> +	 */
> +	nr_fixed_counters = min_t(int, edx.split.num_counters_fixed,
> +				  find_first_zero_bit(kvm_pmu_cap.fixed_cntr_mask,
> +						      KVM_MAX_NR_FIXED_COUNTERS));
> +
> +	fixed_mask = BIT_ULL(nr_fixed_counters) - 1;
> +	fixed_mask &= kvm_pmu_cap.fixed_cntr_mask64;

Isn't nr_fixed_counters already clamped to the number of contiguous bits
in fixed_cntr_mask?

>  
>  	/*
> -	 * The number of counters comes from guest CPUID data. Clamp the value
> -	 * to avoid a shift-by-64 in BIT_ULL().
> +	 * CPUID.0AH:EAX[15:8] can only enumerate contiguous counters. Clamp the
> +	 * value to the number of contiguous GP counters supported by KVM.
>  	 */
> -	nr_gp_counters = min_t(int, eax.split.num_counters, X86_PMC_IDX_MAX - 1);
> -	pmu->pmc_exists64 = (BIT_ULL(nr_gp_counters) - 1) &
> -			    (BIT_ULL(kvm_pmu_cap.num_counters_gp) - 1);
> +	nr_gp_counters = min_t(int, eax.split.num_counters,
> +			       find_first_zero_bit(kvm_pmu_cap.cntr_mask,
> +						   KVM_MAX_NR_GP_COUNTERS));
> +	pmu->pmc_exists64 = BIT_ULL(nr_gp_counters) - 1;
>  
>  	entry = kvm_find_cpuid_entry_index(vcpu, 7, 0);