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

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Message-ID: <4F5E59AC.7090708@zytor.com>
Date:	Mon, 12 Mar 2012 13:16:44 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>, 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 03/12/2012 01:04 PM, H. Peter Anvin wrote:
> On 03/12/2012 01:01 PM, Eric W. Biederman wrote:
>>
>> The basic problem is which source do we block this at?  How many
>> sources are their?  And architecturally last I looked x86 no longer
>> has a NMI disable EFI and similar systems want to get away without
>> a CMOS legacy clock because designers so often get them wrong.
>>
> 
> On all processors which have an LAPIC you can block all NMI sources at
> the LAPIC.  I think it's safe to assume that if you don't have an LAPIC
> -- an ancient system by now -- you have port 70h.
> 

One thing: *disabling* the LAPIC will allow external NMIs coming in on
LINT1 through, since the LAPIC in the disabled state tries to mimic the
no-LAPIC configuration.  So I don't think you want to disable LAPIC as
much as disable the interrupt vectors within.

	-hpa

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