Re: [PATCH RFC] NMI Re-introduce un[set]_nmi_callback

[H. Peter Anvin]

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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