Re: [PATCH v4 05/38] perf: Add generic exclude_guest support

[Namhyung Kim <namhyung@kernel.org>]

On Mon, Mar 24, 2025 at 05:30:45PM +0000, Mingwei Zhang wrote:
> From: Kan Liang <kan.liang@linux.intel.com>
> 
> Only KVM knows the exact time when a guest is entering/exiting. Expose
> two interfaces to KVM to switch the ownership of the PMU resources.
> 
> All the pinned events must be scheduled in first. Extend the
> perf_event_sched_in() helper to support extra flag, e.g., EVENT_GUEST.
> 
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> Signed-off-by: Mingwei Zhang <mizhang@google.com>
> ---
>  include/linux/perf_event.h |  4 ++
>  kernel/events/core.c       | 80 ++++++++++++++++++++++++++++++++++----
>  2 files changed, 77 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 7bda1e20be12..37187ee8e226 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1822,6 +1822,8 @@ extern int perf_event_period(struct perf_event *event, u64 value);
>  extern u64 perf_event_pause(struct perf_event *event, bool reset);
>  int perf_get_mediated_pmu(void);
>  void perf_put_mediated_pmu(void);
> +void perf_guest_enter(void);
> +void perf_guest_exit(void);
>  #else /* !CONFIG_PERF_EVENTS: */
>  static inline void *
>  perf_aux_output_begin(struct perf_output_handle *handle,
> @@ -1919,6 +1921,8 @@ static inline int perf_get_mediated_pmu(void)
>  }
>  
>  static inline void perf_put_mediated_pmu(void)			{ }
> +static inline void perf_guest_enter(void)			{ }
> +static inline void perf_guest_exit(void)			{ }
>  #endif
>  
>  #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 7a2115b2c5c1..d05487d465c9 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -2827,14 +2827,15 @@ static void task_ctx_sched_out(struct perf_event_context *ctx,
>  
>  static void perf_event_sched_in(struct perf_cpu_context *cpuctx,
>  				struct perf_event_context *ctx,
> -				struct pmu *pmu)
> +				struct pmu *pmu,
> +				enum event_type_t event_type)
>  {
> -	ctx_sched_in(&cpuctx->ctx, pmu, EVENT_PINNED);
> +	ctx_sched_in(&cpuctx->ctx, pmu, EVENT_PINNED | event_type);
>  	if (ctx)
> -		 ctx_sched_in(ctx, pmu, EVENT_PINNED);
> -	ctx_sched_in(&cpuctx->ctx, pmu, EVENT_FLEXIBLE);
> +		ctx_sched_in(ctx, pmu, EVENT_PINNED | event_type);
> +	ctx_sched_in(&cpuctx->ctx, pmu, EVENT_FLEXIBLE | event_type);
>  	if (ctx)
> -		 ctx_sched_in(ctx, pmu, EVENT_FLEXIBLE);
> +		ctx_sched_in(ctx, pmu, EVENT_FLEXIBLE | event_type);
>  }
>  
>  /*
> @@ -2890,7 +2891,7 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
>  	else if (event_type & EVENT_PINNED)
>  		ctx_sched_out(&cpuctx->ctx, pmu, EVENT_FLEXIBLE);
>  
> -	perf_event_sched_in(cpuctx, task_ctx, pmu);
> +	perf_event_sched_in(cpuctx, task_ctx, pmu, 0);
>  
>  	for_each_epc(epc, &cpuctx->ctx, pmu, 0)
>  		perf_pmu_enable(epc->pmu);
> @@ -4188,7 +4189,7 @@ static void perf_event_context_sched_in(struct task_struct *task)
>  		ctx_sched_out(&cpuctx->ctx, NULL, EVENT_FLEXIBLE);
>  	}
>  
> -	perf_event_sched_in(cpuctx, ctx, NULL);
> +	perf_event_sched_in(cpuctx, ctx, NULL, 0);
>  
>  	perf_ctx_sched_task_cb(cpuctx->task_ctx, true);
>  
> @@ -6040,6 +6041,71 @@ void perf_put_mediated_pmu(void)
>  }
>  EXPORT_SYMBOL_GPL(perf_put_mediated_pmu);
>  
> +static inline void perf_host_exit(struct perf_cpu_context *cpuctx)
> +{
> +	perf_ctx_disable(&cpuctx->ctx, EVENT_GUEST);
> +	ctx_sched_out(&cpuctx->ctx, NULL, EVENT_GUEST);
> +	perf_ctx_enable(&cpuctx->ctx, EVENT_GUEST);
> +	if (cpuctx->task_ctx) {
> +		perf_ctx_disable(cpuctx->task_ctx, EVENT_GUEST);
> +		task_ctx_sched_out(cpuctx->task_ctx, NULL, EVENT_GUEST);
> +		perf_ctx_enable(cpuctx->task_ctx, EVENT_GUEST);
> +	}
> +}

Cpu context and task context may have events in the same PMU.
How about this?

	perf_ctx_disable(&cpuctx->ctx, EVENT_GUEST);
	if (cpuctx->task_ctx)
		perf_ctx_disable(cpuctx->task_ctx, EVENT_GUEST);

	ctx_sched_out(&cpuctx->ctx, NULL, EVENT_GUEST);
	if (cpuctx->task_ctx)
		task_ctx_sched_out(cpuctx->task_ctx, NULL, EVENT_GUEST);

	if (cpuctx->task_ctx)
		perf_ctx_enable(cpuctx->task_ctx, EVENT_GUEST);
	perf_ctx_enable(&cpuctx->ctx, EVENT_GUEST);

Thanks,
Namhyung

> +
> +/* When entering a guest, schedule out all exclude_guest events. */
> +void perf_guest_enter(void)
> +{
> +	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
> +
> +	lockdep_assert_irqs_disabled();
> +
> +	perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> +
> +	if (WARN_ON_ONCE(__this_cpu_read(perf_in_guest)))
> +		goto unlock;
> +
> +	perf_host_exit(cpuctx);
> +
> +	__this_cpu_write(perf_in_guest, true);
> +
> +unlock:
> +	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
> +}
> +EXPORT_SYMBOL_GPL(perf_guest_enter);
> +
> +static inline void perf_host_enter(struct perf_cpu_context *cpuctx)
> +{
> +	perf_ctx_disable(&cpuctx->ctx, EVENT_GUEST);
> +	if (cpuctx->task_ctx)
> +		perf_ctx_disable(cpuctx->task_ctx, EVENT_GUEST);
> +
> +	perf_event_sched_in(cpuctx, cpuctx->task_ctx, NULL, EVENT_GUEST);
> +
> +	if (cpuctx->task_ctx)
> +		perf_ctx_enable(cpuctx->task_ctx, EVENT_GUEST);
> +	perf_ctx_enable(&cpuctx->ctx, EVENT_GUEST);
> +}
> +
> +void perf_guest_exit(void)
> +{
> +	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
> +
> +	lockdep_assert_irqs_disabled();
> +
> +	perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> +
> +	if (WARN_ON_ONCE(!__this_cpu_read(perf_in_guest)))
> +		goto unlock;
> +
> +	perf_host_enter(cpuctx);
> +
> +	__this_cpu_write(perf_in_guest, false);
> +unlock:
> +	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
> +}
> +EXPORT_SYMBOL_GPL(perf_guest_exit);
> +
>  /*
>   * Holding the top-level event's child_mutex means that any
>   * descendant process that has inherited this event will block
> -- 
> 2.49.0.395.g12beb8f557-goog
>