linux-kernel - Re: [PATCH 1/2] boot: ignore early NMIs

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Message-ID: <4F5D8E63.60606@zytor.com>
Date:	Sun, 11 Mar 2012 22:49:23 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Don Zickus <dzickus@...hat.com>,
	linux-tip-commits@...r.kernel.org, torvalds@...ux-foundation.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, tglx@...utronix.de, mingo@...e.hu,
	Yinghai Lu <yinghai@...nel.org>, akpm@...ux-foundation.org,
	vgoyal@...hat.com
Subject: Re: [PATCH 1/2] boot: ignore early NMIs

On 03/11/2012 10:43 PM, Fernando Luis Vázquez Cao wrote:

> 
> To tackle this issue we can either stop the hardlockup detector
> or disable the LAPIC (the NMIs needed by x86's hardlockup detector
> are generated using performance counters in the LAPIC), leaving
> the I/O APICs untouched. The second is simpler and I think it
> is the approach Don took to fix this issue in RHEL kernels.
> 
> Unfortunately, this is not enough, we are still exposed to external
> NMIs not routed through the LAPIC. In other words, we have to make
> sure that we always have and IDT that is able to handle NMIs without
> seemingly random reboots and lockups. To achieve this goal we need
> to fix machine_kexec() and the early IDT handlers. The current patch
> set takes care of the latter.
> 

The only source of NMIs other than the LAPIC should be the system error
which can be disabled through the RTC port, so I think your second
paragraph here is way more mechanism than you need for very little gain.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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