linux-kernel - Re: [PATCH kvm/queue v2 2/3] perf: x86/core: Add interface to query perfmon_event

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Date:   Wed, 2 Feb 2022 15:43:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Like Xu <likexu@...cent.com>
Subject: Re: [PATCH kvm/queue v2 2/3] perf: x86/core: Add interface to query
 perfmon_event_map[] directly

On Mon, Jan 17, 2022 at 04:53:06PM +0800, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> Currently, we have [intel|knc|p4|p6]_perfmon_event_map on the Intel
> platforms and amd_[f17h]_perfmon_event_map on the AMD platforms.
> 
> Early clumsy KVM code or other potential perf_event users may have
> hard-coded these perfmon_maps (e.g., arch/x86/kvm/svm/pmu.c), so
> it would not make sense to program a common hardware event based
> on the generic "enum perf_hw_id" once the two tables do not match.
> 
> Let's provide an interface for callers outside the perf subsystem to get
> the counter config based on the perfmon_event_map currently in use,
> and it also helps to save bytes.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
>  arch/x86/events/core.c            | 9 +++++++++
>  arch/x86/include/asm/perf_event.h | 2 ++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 38b2c779146f..751048f4cc97 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -693,6 +693,15 @@ void x86_pmu_disable_all(void)
>  	}
>  }
>  
> +u64 perf_get_hw_event_config(int perf_hw_id)
> +{
> +	if (perf_hw_id < x86_pmu.max_events)
> +		return x86_pmu.event_map(perf_hw_id);
> +
> +	return 0;
> +}

Where does perf_hw_id come from? Does this need to be
array_index_nospec() ?

> +EXPORT_SYMBOL_GPL(perf_get_hw_event_config);

Urgh... hate on kvm being a module again. We really need something like
EXPORT_SYMBOL_KVM() or something.


>  struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
>  {
>  	return static_call(x86_pmu_guest_get_msrs)(nr);
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index 8fc1b5003713..d1e325517b74 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -492,9 +492,11 @@ static inline void perf_check_microcode(void) { }
>  
>  #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)
>  extern struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr);
> +extern u64 perf_get_hw_event_config(int perf_hw_id);
>  extern int x86_perf_get_lbr(struct x86_pmu_lbr *lbr);
>  #else
>  struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr);
> +u64 perf_get_hw_event_config(int perf_hw_id);

I think Paolo already spotted this one.

>  static inline int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
>  {
>  	return -1;
> -- 
> 2.33.1
>