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

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Date:	Wed, 9 Jul 2014 11:14:26 +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;

If you fail here;

>  		reg->idx = er->idx;
>  		reg->config = event->attr.config1;

> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
> index adb02aa..2be44be 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -1471,11 +1471,14 @@ static void intel_fixup_er(struct perf_event *event, int idx)
>  {
>  	event->hw.extra_reg.idx = idx;
>  
> -	if (idx == EXTRA_REG_RSP_0) {
> +	/* The extra_reg doesn't update if msrs cannot be accessed safely */
> +	if ((idx == EXTRA_REG_RSP_0) &&
> +			x86_pmu.extra_msr_access[EXTRA_REG_RSP_0]) {
>  		event->hw.config &= ~INTEL_ARCH_EVENT_MASK;
>  		event->hw.config |= x86_pmu.extra_regs[EXTRA_REG_RSP_0].event;
>  		event->hw.extra_reg.reg = MSR_OFFCORE_RSP_0;
> -	} else if (idx == EXTRA_REG_RSP_1) {
> +	} else if ((idx == EXTRA_REG_RSP_1) &&
> +			x86_pmu.extra_msr_access[EXTRA_REG_RSP_1]) {
>  		event->hw.config &= ~INTEL_ARCH_EVENT_MASK;
>  		event->hw.config |= x86_pmu.extra_regs[EXTRA_REG_RSP_1].event;
>  		event->hw.extra_reg.reg = MSR_OFFCORE_RSP_1;

You should never get here..


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