linux-kernel - Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v2)

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Date:	Wed, 16 Apr 2008 15:06:05 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Andi Kleen <andi@...stfloor.org>, akpm@...l.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v2)


* Mathieu Desnoyers <compudj@...stal.dyndns.org> wrote:

> Implements an alternative iret with popf and return so trap and 
> exception handlers can return to the NMI handler without issuing iret. 
> iret would cause NMIs to be reenabled prematurely. x86_32 uses popf 
> and far return. x86_64 has to copy the return instruction pointer to 
> the top of the previous stack, issue a popf, loads the previous esp 
> and issue a near return (ret).

thanks Mathieu, i've picked this up into x86.git for more testing.

note that this also fixes an oprofile regression: when oprofile is used 
to generate stack-backtraces, we can fault on address resolution from 
NMI context and currently we do an IRET - with your fixes it should work 
fine. Obscure case but still worth fixing.

	Ingo
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