linux-kernel - Re: [RFC][PATCH 3/3] x86: Add workaround to NMI iret woes

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Date:	Fri, 9 Dec 2011 18:49:11 +0100
From:	Borislav Petkov <bp@...64.org>
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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Paul Turner <pjt@...gle.com>, Borislav Petkov <bp@...64.org>
Subject: Re: [RFC][PATCH 3/3] x86: Add workaround to NMI iret woes

Hey Steve,

On Fri, Dec 09, 2011 at 12:19:31PM -0500, Steven Rostedt wrote:
> Could you shed some light on this. Can an NMI interrupt an MCE in
> progress?

Easy, http://support.amd.com/us/Processor_TechDocs/APM_V2_24593.pdf,
section 8.5.

On amd64 #MC is along with processor reset the highest prio. Judging
from the text, an NMI occurring during an #MC is held until we return
from the #MC handler:

"When simultaneous interrupts occur, the processor transfers control
to the highest-priority interrupt handler. Lower-priority interrupts
from external sources are held pending by the processor, and they are
handled after the higher-priority interrupt is handled. Lower-priority
interrupts that result from internal sources are discarded. Those
interrupts reoccur when the high-priority interrupt handler completes
and transfers control back to the interrupted instruction."

HTH.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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