linux-kernel - Re: [PATCH] watchdog: hpwdt: Remove spinlock acquire and BIOS calls from NMI context

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Date:   Wed, 14 Feb 2018 10:38:35 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>, Dave Hansen <dave@...1.net>,
        hpa@...or.com, tglx@...utronix.de, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, dwmw@...zon.co.uk,
        linux-tip-commits@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] watchdog: hpwdt: Remove spinlock acquire and BIOS calls
 from NMI context

On Wed, Feb 14, 2018 at 10:31:59AM +0100, Ingo Molnar wrote:
> Because in this particular case it does not appear to be so: the reason for the 
> BIOS/firmware call appears to be to determine how we nmi_panic() after receiving 
> an NMI that no other NMI handler handled: with a passive-aggressive "I don't know" 
> panic message or with a slightly more informative panic message.

However much I like just ripping all that out, I think the ROM call
actually does that logging, or that is how I read things.

If you look at the original Changelog for that driver:

    Hp is providing a Hardware WatchDog Timer driver that will only work with the
    specific HW Timer located in the HP ProLiant iLO 2 ASIC. The iLO 2 HW Timer
    will generate a Non-maskable Interrupt (NMI) 9 seconds before physically
    resetting the server, by removing power, so that the event can be logged to
    the HP Integrated Management Log (IML), a Non-Volatile Random Access Memory
    (NVRAM). The logging of the event is performed using the HP ProLiant ROM via
    an Industry Standard access known as a BIOS Service Directory Entry.