linux-kernel - Re: [RFC][PATCH 5/5 v2] x86: Allow NMIs to hit breakpoints in i386

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Message-ID: <4EE8EA61.9050902@zytor.com>
Date:	Wed, 14 Dec 2011 10:26:41 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [RFC][PATCH 5/5 v2] x86: Allow NMIs to hit breakpoints in i386

On 12/13/2011 06:52 PM, Steven Rostedt wrote:
> With i386, NMIs and breakpoints use the current stack and they
> do not reset the stack pointer to a fix point that might corrupt
> a previous NMI or breakpoint (as it does in x86_64). But NMIs are
> still not made to be re-entrant, and need to prevent the case that
> an NMI hitting a breakpoint (which does an iret), doesn't allow
> another NMI to run.

Okay... what about the other way around: avoiding the IRET when invoked
from an NMI context and therefore leaving NMI disabled until the
appropriate time?

	-hpa


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

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