linux-kernel - Re: [PATCH 1/3] mce: Add a msg string to the MCE tracepoint

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Date:	Wed, 29 Feb 2012 18:19:05 +0100
From:	Borislav Petkov <bp@...64.org>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	EDAC devel <linux-edac@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mce: Add a msg string to the MCE tracepoint

On Wed, Feb 29, 2012 at 05:11:08PM +0000, Luck, Tony wrote:
> >> - on Nehalem, the MCE status register encodes not only the error message; it
> >>   also encodes the DIMM that generated the  error. So, it is possible to 
> >>   completely decode the error on userspace, using only the MCE registers.
> >
> > Well, depending on what Tony wants to do there, either decode the error
> > in the kernel and pass it on with the 'msg' arg or do the whole decoding
> > in userspace.
> 
> For best results - we should decode right away in the kernel. Decoding later
> requires that we carry a lot of additional information about the system
> configuration at the time of the error.  Consider the case of a hard error
> (either fatal or recoverable). If the system reboots, then the DIMM
> with the error should fail self test - and thus be mapped out of the system.
> If the error analyzer doesn't realize that this has happened, it will be
> very confused. Even if it does notice - the Sandy bridge decoder won't be
> able to check that the right DIMM was mapped out (since the configuration
> registers it reads to map addresses to DIMMS will now be set for the new
> configuration, with different mappings).

Absolutely!

And also, you've lost the moment the system reboots and you haven't
gotten all the info needed for decoding the error.


-- 
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Boris.

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