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

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Date:	Mon, 12 Mar 2012 10:41:40 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>,
	"Eric W. Biederman" <ebiederm@...ssion.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 Sun, Mar 11, 2012 at 10:49:23PM -0700, H. Peter Anvin wrote:
> 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.

I forgot about the RTC port.  I can't seem to find the documentation for
it, but I believe it was port 0x70?  That would cover external NMIs I
believe.  Leaving the disable_lapic would cover internal NMIs.

I don't know how far do we want to go with installing stub idt handlers
and such.  Honestly, I just wanted to i/o apic race condition fixed.

http://lkml.indiana.edu/hypermail/linux/kernel/1202.3/02533.html

Cheers,
Don
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