linux-kernel - Re: [PATCH 2/3] x86 perf: Protect LBR msrs accessing against potential #GP

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Message-ID: <20140801132120.GO18735@two.firstfloor.org>
Date:	Fri, 1 Aug 2014 15:21:20 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	kan.liang@...el.com, andi@...stfloor.org,
	alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/3] x86 perf: Protect LBR msrs accessing against
 potential #GP

> > NAK!
> > 
> > I already said this isn't going to ever happen.
> > 
> > Both PT and LBR are arbitrated through the kernel, therefore we can (and
> > must) deny PT when there's existing LBR usage and vice versa.
> > 
> > We will not hijack resources like this full stop end of story.
> > 
> > Fuck hardware/BIOS, they should _NOT_ be touching this.
> > 
> > The 3 people in the world with access to an x86 hardware debugger had
> > better be competent and know WTF they're doing and the BIOS can just
> > piss off right now, they should not be touching this _EVER_.


So you realize that hardware level debugging becomes impossible
if everyone starts using perf?

I dont know how anyone can construct essentially sabotaging powerful
debugging techniques ever as a good thing. In the end it'll just
lead to more buggy software (and likely hardware) for everyone.


> 
> I yelled at BIOS engineers over their PMU usage and $vendor added a BIOS
> knob to disable that, I'll yell at BIOS engineers again, just give me
> their number.
> 
> Really, say NO already.

Ok, so no technical reason, merely a "me vs you" power play.

Thank you for not stating that earlier and wasting everyone's time.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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