linux-kernel - Re: [PATCH V3 1/2] perf ignore LBR and offcore

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Date:	Tue, 8 Jul 2014 16:31:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	"andi@...stfloor.org" <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH V3 1/2] perf ignore LBR and offcore_rsp.

On Tue, Jul 08, 2014 at 02:22:25PM +0000, Liang, Kan wrote:
> > This too is wrong in many ways; there's more than 2 extra_msrs on many
> > systems.
> > 
> Right, there are four extra  reg types on Intel systems. Since my
> previous test only triggers the crash with RSP_0 and RSP_1, so I only
> handle these two msrs.  I will handle all the extra msrs then.

Yeah, so to other two are PEBS related, and I think we disable PEBS
early on so you'll never hit them or something; didn't look too closely.

> > And the place you check is abysmal, if we know at init time that we don't
> > have those MSRs, WTF do you allow event creation that would use them,
> > only to then misbehave?
> 
> Right, we can check it at all the possible creation places.  I think
> the most common place to check should be x86_pmu_extra_regs.  For
> RSP_0 and RSP_1, I also plan to do the check in intel_fixup_er, so
> extra_reg will not be updated.  For LBR select, lbr_sel_map will be
> cleared at runtime once check_msr failed.  Besides the three places,
> is there any place I missed?

I think that's sufficient; but didn't stare too hard.

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