linux-kernel - Re: Perhaps a side effect regarding NMI returns

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Date:	Tue, 29 Nov 2011 13:05:15 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Paul Turner <pjt@...gle.com>
Subject: Re: Perhaps a side effect regarding NMI returns

On Tue, Nov 29, 2011 at 12:58 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Note, the reason that I've been looking at this code, is because I'm
> looking at implementing your idea to handle irets in NMIs, caused by
> faults, exceptions, and the reason I really care about: debugging.
>
> Your proposal is here:
>
>  https://lkml.org/lkml/2010/7/14/264

Ahh, good that you pointed to it, I'd completely forgotten about this one.

Yeah. Simplifying NMI and not mixing up the paranoid stuff sounds like
a good idea, and then if we do the nice NMI counting thing and avoid
the whole problem with NMI and iret, that would be a nice cleanup in
itself.

So if that patch I posted works for you (with some NMI-heavy workload
like non-PEBS tracing) I think it's the way to go.

Too late for 3.2 obviously, since I don't think anybody has actually
reported the "delayed NMI's" as a real problem - so even if it's a
bug, it's not a bug we should try to fix at this stage.

                      Linus
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