[V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option

[河合英宏 / KAWAI，HIDEHIRO]

> On Fri, Sep 25, 2015 at 08:28:11PM +0900, 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.
> 
> So that they can get really stuck when the crash kernel crashes, right?
> ;-)

No, it is different from my intention.

`mistakenly' in the above means; they issue NMI due to a misconception
that the monitored host is stuck in the 1st kernel while it is actually
taking a crash dump in the 2nd kernel.  To avoid this kind of accident,
there is a tool such as fence_kdump which notifies "I'm taking a crash
dump, so don't send NMI" to the HA clustering software.  However, there
is a time window between kernel panic and the notification.

"noextnmi" allows users to avoid this kind of accident all the time of
2nd kernel.

Regards,


Hidehiro Kawai
Hitachi, Ltd. Research & Development Group