linux-kernel - Re: [PATCH V4 1/2] perf ignore LBR and extra

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Date:	Wed, 9 Jul 2014 10:32:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	kan.liang@...el.com
Cc:	andi@...stfloor.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH V4 1/2] perf ignore LBR and extra_regs.

On Tue, Jul 08, 2014 at 09:49:40AM -0700, kan.liang@...el.com wrote:
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 2bdfbff..f0e8022 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -118,6 +118,9 @@ static int x86_pmu_extra_regs(u64 config, struct perf_event *event)
>  			continue;
>  		if (event->attr.config1 & ~er->valid_mask)
>  			return -EINVAL;
> +		/* Check if the extra msrs can be safely accessed*/
> +		if (!x86_pmu.extra_msr_access[er->idx])
> +			continue;
>  
>  		reg->idx = er->idx;
>  		reg->config = event->attr.config1;

You should return an error here; doing continue will eventually make
it return 0, which is no-error and things will happily create the event
and malfunction.

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