linux-kernel - Re: [PATCH v8 05/26] KVM: x86/pmu: Get eventsel for fixed counters from perf

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Message-ID: <2f306eda-953b-4390-8db1-0b3ab4e16213@linux.intel.com>
Date:   Fri, 10 Nov 2023 08:48:39 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dapeng Mi <dapeng1.mi@...ux.intel.com>,
        Jim Mattson <jmattson@...gle.com>,
        Jinrong Liang <cloudliang@...cent.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Like Xu <likexu@...cent.com>
Subject: Re: [PATCH v8 05/26] KVM: x86/pmu: Get eventsel for fixed counters
 from perf



On 2023-11-09 9:12 p.m., Sean Christopherson wrote:
> Get the event selectors used to effectively request fixed counters for
> perf events from perf itself instead of hardcoding them in KVM and hoping
> that they match the underlying hardware.  While fixed counters 0 and 1 use
> architectural events, as of ffbe4ab0beda ("perf/x86/intel: Extend the
> ref-cycles event to GP counters") fixed counter 2 (reference TSC cycles)
> may use a software-defined pseudo-encoding or a real hardware-defined
> encoding.
> 
> Reported-by: Kan Liang <kan.liang@...ux.intel.com>
> Closes: https://lkml.kernel.org/r/4281eee7-6423-4ec8-bb18-c6aeee1faf2c%40linux.intel.com
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks,
Kan
>  arch/x86/kvm/vmx/pmu_intel.c | 30 +++++++++++++++++-------------
>  1 file changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index c9df139efc0c..3bac3b32b485 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -406,24 +406,28 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   * result is the same (ignoring the fact that using a general purpose counter
>   * will likely exacerbate counter contention).
>   *
> - * Note, reference cycles is counted using a perf-defined "psuedo-encoding",
> - * as there is no architectural general purpose encoding for reference cycles.
> + * Forcibly inlined to allow asserting on @index at build time, and there should
> + * never be more than one user.
>   */
> -static u64 intel_get_fixed_pmc_eventsel(int index)
> +static __always_inline u64 intel_get_fixed_pmc_eventsel(unsigned int index)
>  {
> -	const struct {
> -		u8 event;
> -		u8 unit_mask;
> -	} fixed_pmc_events[] = {
> -		[0] = { 0xc0, 0x00 }, /* Instruction Retired / PERF_COUNT_HW_INSTRUCTIONS. */
> -		[1] = { 0x3c, 0x00 }, /* CPU Cycles/ PERF_COUNT_HW_CPU_CYCLES. */
> -		[2] = { 0x00, 0x03 }, /* Reference Cycles / PERF_COUNT_HW_REF_CPU_CYCLES*/
> +	const enum perf_hw_id fixed_pmc_perf_ids[] = {
> +		[0] = PERF_COUNT_HW_INSTRUCTIONS,
> +		[1] = PERF_COUNT_HW_CPU_CYCLES,
> +		[2] = PERF_COUNT_HW_REF_CPU_CYCLES,
>  	};
> +	u64 eventsel;
>  
> -	BUILD_BUG_ON(ARRAY_SIZE(fixed_pmc_events) != KVM_PMC_MAX_FIXED);
> +	BUILD_BUG_ON(ARRAY_SIZE(fixed_pmc_perf_ids) != KVM_PMC_MAX_FIXED);
> +	BUILD_BUG_ON(index >= KVM_PMC_MAX_FIXED);
>  
> -	return (fixed_pmc_events[index].unit_mask << 8) |
> -		fixed_pmc_events[index].event;
> +	/*
> +	 * Yell if perf reports support for a fixed counter but perf doesn't
> +	 * have a known encoding for the associated general purpose event.
> +	 */
> +	eventsel = perf_get_hw_event_config(fixed_pmc_perf_ids[index]);
> +	WARN_ON_ONCE(!eventsel && index < kvm_pmu_cap.num_counters_fixed);
> +	return eventsel;
>  }
>  
>  static void intel_pmu_refresh(struct kvm_vcpu *vcpu)