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Date: Thu, 04 Sep 2008 08:12:59 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Prarit Bhargava <prarit@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
       linux-kernel@vger.kernel.org, arozansk@redhat.com, dzickus@redhat.com,
       Thomas.Mingarelli@hp.com, ak@linux.intel.com,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Thomas Gleixner <tglx@linutronix.de>,
       "Maciej W. Rozycki" <macro@linux-mips.org>
Subject: Re: [PATCH RFC] NMI Re-introduce un[set]_nmi_callback
References: <20080904130048.31841.3329.sendpatchset@prarit.bos.redhat.com> <1220535463.8609.223.camel@twins> <48BFF0C0.7060208@redhat.com> <20080904145617.GB28095@elte.hu>
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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