linux-kernel - Re: [Xen-devel] [PATCH 1/3] Add mcelog support for xen platform

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Message-ID: <20120423153222.GE24481@phenom.dumpdata.com>
Date:	Mon, 23 Apr 2012 11:32:22 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Borislav Petkov <bp@...64.org>,
	"Liu, Jinsong" <jinsong.liu@...el.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Xen-devel] [PATCH 1/3] Add mcelog support for xen platform

On Mon, Apr 23, 2012 at 03:27:32PM +0000, Luck, Tony wrote:
> > Because, if you'd hooked into it, just imagine one fine day, when we
> > remove mcelog support, what screaming the xen people will be doing when
> > mcelog doesn't work anymore.
> 
> Agreed. Even before we get to deleting mcelog, "struct mce" can change (new
> fields could be added) ... and you don't want to have your hypervisor to
> have to know which version of Linux it is talking to.

I am having a hard time seeing how this is different from 'struct mce'
changing and the hardware remaining the same?

Can't the MCE check drivers deal with that - I mean that is their purpose -
to extract some "blob" of data from the hardware, massage it in the software
structure, and send its way. If you add some more fields in the software
structure - either the hardware can provide it or not. If not, it will have
to emulate it. This would be the same case with this driver.

This driver is _not_ doing a strict bit-by-bit copy of 'struct mcinfo'
to 'struct mce'. It is plucking the right bits and setting them in
'struct mce'.
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