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

Date: Tue Oct 27 2015 - 05:01:28 EST


> I just have a look at this thread. I am wondering why we don't use
> existing is_kdump_kernel() directly to disable external NMI if it's
> in kdump kernel. Then no need to introduce another boot option "noextnmi"
> which is used only for kdump kernel.

As I stated in another mail, there is a case where we don't want to
mask external NMIs in the second kernel. So, we need some
configurable way. Please see the following quotation.

> We souldn't enable this feature silently. Some users wouldn't like
> to enable this feature. For example, a user enables a watchdog timer
> which raises an external NMI when the counter is not reset for a
> specific duration. Then, the second kernel hangs up while saving
> crash dump, and NMI is delivered to the CPU. The kernel gets panic
> due to the NMI, prints some information to the display and serial
> console, and then automatically reboot. In this case, users don't
> want to block external NMIs.


Hidehiro Kawai
Hitachi, Ltd. Research & Development Group