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Message-ID: <48BFFAFB.6060907@zytor.com>
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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