linux-kernel - RE: [RFC PATCH v2 1/3] perf/core: Expose perf_event_{en,dis}able

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Date:   Thu, 22 Sep 2022 12:16:10 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Arnaldo Carvalho de Melo" <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Alexander Shishkin" <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>
CC:     "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [RFC PATCH v2 1/3] perf/core: Expose
 perf_event_{en,dis}able_local()

On Thursday, September 22, 2022 12:45 AM, Li, Xiaoyao wrote:
> KVM needs them to disable/enable an Intel PT perf event before vm-entry/after
> vm-exit.

I would explain more in the commit here:

Export perf_event_disable_local and perf_event_enable_local for perf users to disable
and enable perf events on the current local CPU. One usage is in PT virtualization
by KVM:
- before VMEnter to guest, KVM calls perf_event_disable_local to disable the host PT event
running on the current CPU, and this reuses the PT driver to save the related h/w states. 
- after VMExit to host, KVM calls perf_event_enable_local to resume the host PT event on
the current CPU by having the PT driver load the previously saved states into h/w.

> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
>  include/linux/perf_event.h | 1 +
>  kernel/events/core.c       | 7 +++++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index
> ee8b9ecdc03b..fc5f3952d6a2 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1472,6 +1472,7 @@ extern int
> perf_swevent_get_recursion_context(void);
>  extern void perf_swevent_put_recursion_context(int rctx);  extern u64
> perf_swevent_set_period(struct perf_event *event);  extern void
> perf_event_enable(struct perf_event *event);
> +extern void perf_event_enable_local(struct perf_event *event);
>  extern void perf_event_disable(struct perf_event *event);  extern void
> perf_event_disable_local(struct perf_event *event);  extern void
> perf_event_disable_inatomic(struct perf_event *event); diff --git
> a/kernel/events/core.c b/kernel/events/core.c index
> 2621fd24ad26..8324bb99c6bf 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -2446,6 +2446,7 @@ void perf_event_disable_local(struct perf_event
> *event)  {
>  	event_function_local(event, __perf_event_disable, NULL);  }
> +EXPORT_SYMBOL_GPL(perf_event_disable_local);
> 
>  /*
>   * Strictly speaking kernel users cannot create groups and therefore this @@
> -2984,6 +2985,12 @@ static void _perf_event_enable(struct perf_event *event)
>  	event_function_call(event, __perf_event_enable, NULL);  }
> 
> +void perf_event_enable_local(struct perf_event *event) {
> +	event_function_local(event, __perf_event_enable, NULL); }
> +EXPORT_SYMBOL_GPL(perf_event_enable_local);
> +
>  /*
>   * See perf_event_disable();
>   */
> --
> 2.27.0