linux-kernel - Re: [PATCH v4 09/38] perf: Add switch_guest

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Message-ID: <20250425111256.GE1166@noisy.programming.kicks-ass.net>
Date: Fri, 25 Apr 2025 13:12:56 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mingwei Zhang <mizhang@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>, Liang@...gle.com,
	Kan <kan.liang@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
	Yongwei Ma <yongwei.ma@...el.com>,
	Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>,
	Jim Mattson <jmattson@...gle.com>,
	Sandipan Das <sandipan.das@....com>,
	Zide Chen <zide.chen@...el.com>,
	Eranian Stephane <eranian@...gle.com>,
	Shukla Manali <Manali.Shukla@....com>,
	Nikunj Dadhania <nikunj.dadhania@....com>
Subject: Re: [PATCH v4 09/38] perf: Add switch_guest_ctx() interface

On Mon, Mar 24, 2025 at 05:30:49PM +0000, Mingwei Zhang wrote:

> @@ -1822,7 +1835,7 @@ 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_enter(u32 guest_lvtpc);
>  void perf_guest_exit(void);
>  #else /* !CONFIG_PERF_EVENTS: */
>  static inline void *
> @@ -1921,7 +1934,7 @@ 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_enter(u32 guest_lvtpc)		{ }
>  static inline void perf_guest_exit(void)			{ }
>  #endif
>  
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index d05487d465c9..406b86641f02 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -451,6 +451,7 @@ static inline bool is_include_guest_event(struct perf_event *event)
>  static LIST_HEAD(pmus);
>  static DEFINE_MUTEX(pmus_lock);
>  static struct srcu_struct pmus_srcu;
> +static DEFINE_PER_CPU(struct mediated_pmus_list, mediated_pmus);
>  static cpumask_var_t perf_online_mask;
>  static cpumask_var_t perf_online_core_mask;
>  static cpumask_var_t perf_online_die_mask;
> @@ -6053,8 +6054,26 @@ static inline void perf_host_exit(struct perf_cpu_context *cpuctx)
>  	}
>  }
>  
> +static void perf_switch_guest_ctx(bool enter, u32 guest_lvtpc)
> +{
> +	struct mediated_pmus_list *pmus = this_cpu_ptr(&mediated_pmus);
> +	struct perf_cpu_pmu_context *cpc;
> +	struct pmu *pmu;
> +
> +	lockdep_assert_irqs_disabled();
> +
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(cpc, &pmus->list, mediated_entry) {
> +		pmu = cpc->epc.pmu;
> +
> +		if (pmu->switch_guest_ctx)
> +			pmu->switch_guest_ctx(enter, (void *)&guest_lvtpc);
> +	}
> +	rcu_read_unlock();
> +}
> +
>  /* When entering a guest, schedule out all exclude_guest events. */
> -void perf_guest_enter(void)
> +void perf_guest_enter(u32 guest_lvtpc)
>  {
>  	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
>  
> @@ -6067,6 +6086,8 @@ void perf_guest_enter(void)
>  
>  	perf_host_exit(cpuctx);
>  
> +	perf_switch_guest_ctx(true, guest_lvtpc);
> +
>  	__this_cpu_write(perf_in_guest, true);
>  
>  unlock:

This, I'm still utterly hating on that lvtpc argument. That doesn't
belong here. Make it go away.