linux-kernel - Re: [PATCH 0/3] Fix MCE handling for AMD multi-node processors

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Date:	Tue, 23 Dec 2014 00:19:29 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	tony.luck@...el.com, dougthompson@...ssion.com,
	mchehab@....samsung.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	dave.hansen@...ux.intel.com, mgorman@...e.de, bp@...e.de,
	riel@...hat.com, jacob.w.shin@...il.com
Subject: Re: [PATCH 0/3] Fix MCE handling for AMD multi-node processors

On Mon, Dec 22, 2014 at 02:56:47PM -0600, Aravind Gopalakrishnan wrote:
> On 12/22/2014 2:15 PM, Borislav Petkov wrote:
> >On Mon, Dec 22, 2014 at 02:10:09PM -0600, Aravind Gopalakrishnan wrote:
> >>When a MCE happens that is to be logged onto bank 4 of AMD multi-node
> >>processors, they are reported only to corresponding node base core of
> >>the cpu on which the error occurred.
> >>
> >>Refer D18F3x44[NbMcaToMstCpuEn] on BKDGs of Fam10h and later for
> >Let me try to understand this correctly:
> >
> >Does that mean that we could fix this by simply doing:
> >
> >D18F3x44[NbMcaToMstCpuEn]=0b
> >
> >on each NB?
> >
> 
> Not quite..
> When this field is 0, BKDG says the error may be reported to the core that
> originated the request *if applicable and known*
> Looking at the error signatures table for MC4 (Part 2),
> we can see only some errors have 'ErrCoreId' column as valid
> 
> Besides, if IO originated the request, then it is reported only to NBC.
> 
> So, to take care of all these cases, I am just following one approach here:
> and that is to look at NBC MSRs for any bank 4 errors.
> (It seems to be what the BKDG recommends anyway as BIOS by default should
> set D18F3x44[NbMcaToMstCpuEn])

Then in that case you have to check the case where
D18F3x44[NbMcaToMstCpuEn] is 0 for whatever reason (some BIOS forgot to
set it or whatever) and to set it again.

Then, upon a quick scan, your patches are adding a lot of vendor-specific
stuff which doesn't belong in the #MC handler, should probably be
wrapped or so, no good idea right now.

Then, you're using rd/wrmsr_on_cpu which does smp_call_function_single()
which can deadlock in atomic context and #MC is one.

Also, the math in amd_get_nbc_for_node() is too fragile and will break
the moment some BIOS renumbers cores to accomodate some other OS.

In any case, I won't be able to take a detailed look soon with the
holidays coming up.

Also, I'm wondering if this can't be solved much more elegantly
by detecting that condition (bank == 4) in the #MC handler and
issuing an IPI before exiting it using irq_work which will schedule
do_machine_check on the NBC. And that should be even easier to do since
we're moving the #MC handler out of the IST and to the normal kernel
stack for 3.20, which would make this endeavor pretty cheap.

Anyway, just a couple of thoughts...

-- 
Regards/Gruss,
    Boris.

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