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

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Message-ID: <5499C57B.5030900@amd.com>
Date:	Tue, 23 Dec 2014 13:41:47 -0600
From:	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>
To:	Borislav Petkov <bp@...en8.de>
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 12/22/2014 5:19 PM, Borislav Petkov wrote:
> 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.
Okay.

> 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.

Ok. I'll look into this approach too over the holidays and we can 
restart the discussion
at a more convenient time.

> Anyway, just a couple of thoughts...
>

Thanks,
-Aravind.
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