linux-kernel - Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods

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Message-ID: <4A37B8CF.8090804@zytor.com>
Date:	Tue, 16 Jun 2009 08:22:55 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, paulus@...ba.org, acme@...hat.com,
	linux-kernel@...r.kernel.org, penberg@...helsinki.fi,
	vegard.nossum@...il.com, efault@....de, jeremy@...p.org,
	npiggin@...e.de, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain	support
 to use NMI-safe methods

Mathieu Desnoyers wrote:
> 
> With respect to cr2, yes, this is the only window we care about.
> However, the rest of vmalloc_fault() must be audited for other non
> nmi-suitable data structure use (e.g. "current"), which I did in the
> past.
> 
> My intent was just to respond to Peter's concerns by showing that the
> part of page fault handler which needs to be NMI-reentrant is really not
> that big.
> 

Even if that is true now, you want it to be true for all future time,
and all to support an out-of-tree piece of code.  All of this is
virtually impossible to test for without said out-of-tree piece of code,
so I will object to it anyway.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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