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

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Date:	Mon, 15 Jun 2009 11:30:05 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Ingo Molnar <mingo@...e.hu>, mingo@...hat.com, hpa@...or.com,
	paulus@...ba.org, acme@...hat.com, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, 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



On Mon, 15 Jun 2009, Mathieu Desnoyers wrote:
> 
> Hrm, would it be possible to save the c2 register upon nmi handler entry
> and restore it before iret instead ?

Yes, that would work as well, and be less subtle.

It still does have the same worries about CPU's not being all that happy 
about writing to %cr2 (we do it when restoring CPU state at resume time, 
but nobody has ever _cared_ before, so I don't know if it matters).

		Linus
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