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

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Date:	Tue, 13 Mar 2012 11:11:49 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
To:	"H. Peter Anvin" <hpa@...or.com>
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 03/13/2012 05:16 AM, H. Peter Anvin wrote:
> 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.

Does this sound like a plan to get the ball rolling?:

1.- Merge Don's patch to disable the LAPIC in kdump reboot path (this
   fixes a real issue seen in the field, is a net win and certainly not a
   regression - indeed it makes the code simpler because the I/O
   APICs are left untouched).

2.- Merge my patch set to ignore early NMIs (this brings the behavior
   of the boot code in line with what we do in the rest of the kernel
   a we can avoid situations were a spurious NMI causes the kernel
   to halt). The early NMI handler is temporary and the final NMI
   handler installed shortly afterwards will take care of subsequent
   NMIs.

3.- Make sure that spurious NMIs (i.e. NMIs that for whatever reason
   could not be stopped at the source) received during the reboot
   path to the kdump kernel do not cause a triple fault or a system
   lockup. This is under testing.

4.- Identify all the NMI sources and keep them from reaching the CPU
   when it can be done in a race-free way.

Can we get 1 and 2 merged while we work on further improvements
(3 and 4)?

Thanks,
Fernando
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