linux-kernel - Re: [PATCH 1/2] x86: mce: kdump: use under_crashdumping to turn off MCE in all CPUs together

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Date:	Tue, 24 Feb 2015 10:56:16 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Naoya Horiguchi <nao.horiguchi@...il.com>,
	Tony Luck <tony.luck@...el.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Junichi Nomura <j-nomura@...jp.nec.com>,
	Kiyoshi Ueda <k-ueda@...jp.nec.com>
Subject: Re: [PATCH 1/2] x86: mce: kdump: use under_crashdumping to turn off
 MCE in all CPUs together

On Tue, Feb 24, 2015 at 08:15:35AM +0000, Naoya Horiguchi wrote:
> Let me update my explanation about the problem. I wrote the description about
> race window of nmi shoot down threads. That's not wrong, but that's only the
> part of the problem. The more suitable description is that all "shot down"
> CPUs keep MCE enabled (disable_local_APIC() doesn't stop it) after entering
> infinite loop of cpu_relax(), so any MCE event causes kernel panic due to
> synchronization timeout whenever after the 2nd kernel launches on the crashing
> CPU (where the CPU don't run do_machine_check(), but the other CPUs do).

Ok, now we're getting closer.

So, I'm thinking you want to disable MCA on all cores going offline
as part of the work done in crash_nmi_callback(). And off the top
of my head, it should be something what mcheck_cpu_init() and
__mcheck_cpu_init_generic() in particular does but in reverse.

I'd even venture a guess and say that clearing CR4.MCE should be enough
but I *think* that doesn't prevent errors from being logged. Just to be
extra sure, you should clear MCG_CTL bits too. It all depends on what
exactly you want to do.

HTH.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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