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Date: Tue, 13 Oct 2015 22:22:58 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option
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To: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: x86@kernel.org, Jonathan Corbet <corbet@lwn.net>, Peter Zijlstra <peterz@infradead.org>, linux-doc@vger.kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Michal Hocko <mhocko@kernel.org>, Ingo Molnar <mingo@redhat.com>, "Eric W. Biederman" <ebiederm@xmission.com>, "H. Peter Anvin" <hpa@zytor.com>, Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>, Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@kernel.org>, Vivek Goyal <vgoyal@redhat.com>

On Fri, 25 Sep 2015, Hidehiro Kawai wrote:

> This patch introduces new boot option "noextnmi" which disables
> external NMI.  This option is useful for the dump capture kernel
> so that an HA application or administrator wouldn't mistakenly
> shoot down the kernel by NMI.
> 
> Currently, only x86 supports this option.

You might add that is can be used for debugging purposes as
well. External NMIs can be their own source of trouble. :)
 
> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> ---
>  Documentation/kernel-parameters.txt |    4 ++++
>  arch/x86/kernel/apic/apic.c         |   17 ++++++++++++++++-
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 22a4b68..8bcaccd 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2379,6 +2379,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			noexec=on: enable non-executable mappings (default)
>  			noexec=off: disable non-executable mappings
>  
> +	noextnmi	[X86]
> +			Mask external NMI.  This option is useful for a
> +			dump capture kernel to be shot down by NMI.

That should read: "...not to be shot down", right?

Other than that.

Acked-by: Thomas Gleixner <tglx@linutronix.de>

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