linux-kernel - Re: [PATCH RFC] NMI Re-introduce un[set]_nmi

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Date:	Thu, 04 Sep 2008 08:12:59 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Prarit Bhargava <prarit@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, arozansk@...hat.com,
	dzickus@...hat.com, Thomas.Mingarelli@...com, ak@...ux.intel.com,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: [PATCH RFC] NMI Re-introduce un[set]_nmi_callback

Ingo Molnar wrote:
> 
> i'd much rather attack this general problem from this angle:
> 
>   static inline unsigned char get_nmi_reason(void)
>   {
>           return inb(0x61);
>   }
> 
> that port 61H read is both arcane (on modern chipsets) and broken on 
> multiple levels. It's racy and SMP unsafe to begin with, if there's any 
> mixture of intentional cross-CPU or CPU self-generated NMIs mixed with 
> chipset generated NMIs.
> 
> One possible approach would be to get rid of it, and to perhaps register 
> a low-priority die notifier on systems where we know port 61 
> reads+writes to be safe and desired. Modern systems will emit MCEs in 
> most cases anyway, not NMIs.
> 

I believe we should still do it, but as the lowest priority "nothing 
else claimed this".  It reflects a system error and not all systems will 
generate #MC instead of NMI for all system errors.

Pretty much what you're saying above.

	-hpa
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