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Subject: Re: [PATCH] KVM: x86: Adjust counter sample period after a wrmsr
To:     Eric Hankland <ehankland@google.com>,
        Jim Mattson <jmattson@google.com>,
        Peter Shier <pshier@google.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org
References: <20200222023413.78202-1-ehankland@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <9adcb973-7b60-71dd-636d-1e451e664c55@redhat.com>
Date:   Sat, 22 Feb 2020 08:34:38 +0100
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On 22/02/20 03:34, Eric Hankland wrote:
> The sample_period of a counter tracks when that counter will
> overflow and set global status/trigger a PMI. However this currently
> only gets set when the initial counter is created or when a counter is
> resumed; this updates the sample period after a wrmsr so running
> counters will accurately reflect their new value.
> 
> Signed-off-by: Eric Hankland <ehankland@google.com>
> ---
>  arch/x86/kvm/pmu.c           | 4 ++--
>  arch/x86/kvm/pmu.h           | 8 ++++++++
>  arch/x86/kvm/vmx/pmu_intel.c | 6 ++++++
>  3 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index bcc6a73d6628..d1f8ca57d354 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -111,7 +111,7 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
>  		.config = config,
>  	};
>  
> -	attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc);
> +	attr.sample_period = get_sample_period(pmc, pmc->counter);
>  
>  	if (in_tx)
>  		attr.config |= HSW_IN_TX;
> @@ -158,7 +158,7 @@ static bool pmc_resume_counter(struct kvm_pmc *pmc)
>  
>  	/* recalibrate sample period and check if it's accepted by perf core */
>  	if (perf_event_period(pmc->perf_event,
> -			(-pmc->counter) & pmc_bitmask(pmc)))
> +			      get_sample_period(pmc, pmc->counter)))
>  		return false;
>  
>  	/* reuse perf_event to serve as pmc_reprogram_counter() does*/
> diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
> index 13332984b6d5..354b8598b6c1 100644
> --- a/arch/x86/kvm/pmu.h
> +++ b/arch/x86/kvm/pmu.h
> @@ -129,6 +129,15 @@ static inline struct kvm_pmc *get_fixed_pmc(struct kvm_pmu *pmu, u32 msr)
>  	return NULL;
>  }
>  
> +static inline u64 get_sample_period(struct kvm_pmc *pmc, u64 counter_value)
> +{
> +	u64 sample_period = (-counter_value) & pmc_bitmask(pmc);
> +
> +	if (!sample_period)
> +		sample_period = pmc_bitmask(pmc) + 1;
> +	return sample_period;
> +}
> +
>  void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel);
>  void reprogram_fixed_counter(struct kvm_pmc *pmc, u8 ctrl, int fixed_idx);
>  void reprogram_counter(struct kvm_pmu *pmu, int pmc_idx);
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index fd21cdb10b79..e933541751fb 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -263,9 +263,15 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  			if (!msr_info->host_initiated)
>  				data = (s64)(s32)data;
>  			pmc->counter += data - pmc_read_counter(pmc);
> +			if (pmc->perf_event)
> +				perf_event_period(pmc->perf_event,
> +						  get_sample_period(pmc, data));
>  			return 0;
>  		} else if ((pmc = get_fixed_pmc(pmu, msr))) {
>  			pmc->counter += data - pmc_read_counter(pmc);
> +			if (pmc->perf_event)
> +				perf_event_period(pmc->perf_event,
> +						  get_sample_period(pmc, data));
>  			return 0;
>  		} else if ((pmc = get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0))) {
>  			if (data == pmc->eventsel)
> 

Queued, thanks.

Paolo