linux-kernel - Re: [Patch] MCE, APEI: Don't enable CMCI when Firmware First mode is set in HEST for corrected machine checks

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Message-ID: <20130512144708.GA5589@pd.tnic>
Date:	Sun, 12 May 2013 16:47:08 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Max Asbock <masbock@...ux.vnet.ibm.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	"naveen.n.rao@...ibm.com" <naveen.n.rao@...ibm.com>,
	"ananth@...ibm.com" <ananth@...ibm.com>,
	"lcm@...ux.vnet.ibm.com" <lcm@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [Patch] MCE, APEI: Don't enable CMCI when Firmware First mode is
 set in HEST for corrected machine checks

And I was wondering why this is not reaching lkml. Fixed.

On Fri, May 10, 2013 at 10:59:04AM -0700, Max Asbock wrote:
> I'll try to summarize the situation:
> 
> We proposed two iterations of a patch that would parse HEST for a
> Corrected Machine Check entry and cause CMCI to be disabled if the
> Firmware First flag was found to be on in that entry.
> Several shortcomings of this approach were subsequently pointed out:
> a) Disabling CMCI doesn't go far enough. If the firmware wants to
> control corrected machine checks then we shouldn't even be polling the
> MCi_STATUS registers. Therefore we need to disable CMCI and disable
> polling if FF is set.
> 
> b) The firmware may take over only a subset of the possible corrected
> machine check events. If we turn off CMCI (and polling) for all banks we
> may miss out on some types of errors. Therefore we should not
> indiscriminately disable CMCI on all banks.
> 
> The question arose whether the APEI spec allows to specify individual
> machine check banks which fall under FF control. The answer appears to
> be 'possibly'. The Corrected Machine Check (CMC) structure defined in
> the APEI spec allows for a list of Machine Check Bank structures which
> could be used to designate a set of banks falling under FF control.
> However, the spec is silent on how the list of Machine Check Bank
> structures in the CMC structure is be used. 
> 
> Further steps in this endeavor may depend on the interpretation of the
> CMC structure in APEI an whether we can specify individual machine check
> banks that fall under FF control.

Right, so we need a complete solution where all FF banks are excluded
from polling. The question is, does the CMC table in APEI enumerate
*all* FF banks or we need to parse something else too.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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