linux-kernel - Re: [PATCH v2 1/2] x86: mce: kexec: turn off MCE in kexec

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Message-ID: <20150227120648.GA3337@pd.tnic>
Date:	Fri, 27 Feb 2015 13:06:48 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.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 v2 1/2] x86: mce: kexec: turn off MCE in kexec

On Fri, Feb 27, 2015 at 06:09:52AM -0500, Prarit Bhargava wrote:
> What if the system is actually having problems with MCE errors --
> which are leading to system panics of some sort. Do you *really* want
> the system to continue on at that point?

No one said that disabling MCA and doing kdump is a 100% reliable thing.

When CR4.MCE=0b and an MCE happens, it will shutdown the system, at
least on Intel, according to Tony. On AMD, disabling error reporting in
addition leads to CR4.MCE being ignored.

In any case, disabling MCA contains a risk kdump should be willing to
take. Let's ask the reverse question: is kdump prepared to handle an MCE
when one happens during dumping?

If we have to be really correct, kdump should actually be prepared
to handle MCEs and in the case where it cannot recover, stop dumping
because the already dumped data might be faulty and corrupted... And
print a nasty message on the screen...

-- 
Regards/Gruss,
    Boris.

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