linux-kernel - Re: [PATCH v4 05/38] perf: Add generic exclude

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Message-ID: <aCUlCApeDM9Uy4a0@google.com>
Date: Wed, 14 May 2025 16:19:36 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Mingwei Zhang <mizhang@...gle.com>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	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 05/38] perf: Add generic exclude_guest support

On Fri, Apr 25, 2025, Peter Zijlstra wrote:
> On Mon, Mar 24, 2025 at 05:30:45PM +0000, Mingwei Zhang wrote:
> 
> > @@ -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);
> > +	}
> > +}
> > +
> > +/* 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);
> 
> This naming is confusing on purpose? Pick either guest/host and stick
> with it.

+1.  I also think the inner perf_host_{enter,exit}() helpers are superflous.
These flows

After a bit of hacking, and with a few spoilers, this is what I ended up with
(not anywhere near fully tested).  I like following KVM's kvm_xxx_{load,put}()
nomenclature to tie everything together, so I went with "guest" instead of "host"
even though the majority of work being down is to shedule out/in host context.

/* When loading a guest's mediated PMU, schedule out all exclude_guest events. */
void perf_load_guest_context(unsigned long data)
{
	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(guest_ctx_loaded)))
		goto unlock;

	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);
	}

	arch_perf_load_guest_context(data);

	__this_cpu_write(guest_ctx_loaded, true);

unlock:
	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
}
EXPORT_SYMBOL_GPL(perf_load_guest_context);

void perf_put_guest_context(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(guest_ctx_loaded)))
		goto unlock;

	arch_perf_put_guest_context();

	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);

	__this_cpu_write(guest_ctx_loaded, false);
unlock:
	perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
}
EXPORT_SYMBOL_GPL(perf_put_guest_context);