linux-kernel - Re: [PATCH] arm_pmu: Validate single/group leader events

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Date:   Mon, 11 Apr 2022 11:04:26 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Rob Herring <robh@...nel.org>
Cc:     Will Deacon <will@...nel.org>, Al Grant <al.grant@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm_pmu: Validate single/group leader events

Hi Rob,

On Fri, Apr 08, 2022 at 03:33:30PM -0500, Rob Herring wrote:
> In the case where there is only a cycle counter available (i.e.
> PMCR_EL0.N is 0) and an event other than CPU cycles is opened, the open
> should fail as the event can never possibly be scheduled. However, the
> event validation when an event is opened is skipped when the group
> leader is opened. Fix this by always validating the group leader events.
> 
> Reported-by: Al Grant <al.grant@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Rob Herring <robh@...nel.org>

This looks obviously correct to me, so FWIW:

Acked-by: Mark Rutland <mark.rutland@....com>

Just to check, have you tested this (e.g. by running on a platform with
PMCR_EL0.N == 0, or hacking the PMU probing to report just the cycle counter)

Thanks,
Mark.

> ---
>  drivers/perf/arm_pmu.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index 9694370651fa..59d3980b8ca2 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -400,6 +400,9 @@ validate_group(struct perf_event *event)
>  	if (!validate_event(event->pmu, &fake_pmu, leader))
>  		return -EINVAL;
>  
> +	if (event == leader)
> +		return 0;
> +
>  	for_each_sibling_event(sibling, leader) {
>  		if (!validate_event(event->pmu, &fake_pmu, sibling))
>  			return -EINVAL;
> @@ -489,12 +492,7 @@ __hw_perf_event_init(struct perf_event *event)
>  		local64_set(&hwc->period_left, hwc->sample_period);
>  	}
>  
> -	if (event->group_leader != event) {
> -		if (validate_group(event) != 0)
> -			return -EINVAL;
> -	}
> -
> -	return 0;
> +	return validate_group(event);
>  }
>  
>  static int armpmu_event_init(struct perf_event *event)
> -- 
> 2.32.0
>