linux-kernel - Re: [PATCH RFC 2/2] events/hw_event: Create a Hardware Anomaly Report Mechanism (HARM)

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Message-ID: <AANLkTi=jGB_nFO0nnWWZ60gqgdELAQjv5dpAZmz5zKSz@mail.gmail.com>
Date:	Fri, 25 Mar 2011 15:37:59 -0700
From:	Tony Luck <tony.luck@...el.com>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
Cc:	Borislav Petkov <bp@...64.org>, Borislav Petkov <bp@...en8.de>,
	Linux Edac Mailing List <linux-edac@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 2/2] events/hw_event: Create a Hardware Anomaly Report
 Mechanism (HARM)

On Fri, Mar 25, 2011 at 2:22 PM, Mauro Carvalho Chehab
<mchehab@...hat.com> wrote:
> Em 25-03-2011 11:13, Borislav Petkov escreveu:
>> However, there's
>> another issue with fatal errors - you want to execute as less code as
>> possible in the wake of a fatal error.
>
> Yes. That's one of the reasons why it may make sense to have a separate event
> for fatal errors.

We have three categories (severities):
1) Corrected - log these
2) Uncorrected-but-not-immediately-fatal - log these too
3) Fatal - all we can do with these is log to some persistent store (or
    to a serial console connected to a logging device). perf style event
    tracing doesn't help when all the userland daemons will never get a
    chance to run.

> It would be good to use some non-volatile ram for these. I was told that
> APEI spec defines a way for that, but I'm not sure if low end machines would
> be shipped with that.

You are talking about ERST - and you are right, this is generally not going
to be present on low-end machines.  drivers/acpi/apei/erst.c was accepted
in 2.6.35.  My /dev/pstore changes are in the current merge for 2.6.39 (but
currently only show dmesg traces to the user).

> Alternatively, edac could fill a translation table, and the decoding code at
> mce would be just a table retrieve routine (in order to speed-up translation,
> in the case of fatal errors.

Eventually the translation table should move above edac (to the drivers/ras/
area that Borislav suggested earlier?) so that both mce and edac can access.
I think we'll need this for some time as SMBIOS continues to disappoint
me with its inaccuracies.

-Tony
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