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

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Date:	Mon, 23 Apr 2012 16:17:03 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	Borislav Petkov <bp@...64.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"Luck, Tony" <tony.luck@...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>,
	Jan Beulich <jbeulich@...e.com>
Subject: RE: [Xen-devel] [PATCH 1/3] Add mcelog support for xen platform

>> 
>> This driver is not that much different from the APEI bridge to MCE
>> code - 
>> it just that instead of reading APEI blob data it reads it from an
>> hypercall. 
> 
> Let me ask you this: is APEI a virtualization solution of some sort?
> 
> No, it is the old windoze RAS crap but I guess Linux has to support it
> now too through BIOS. And x86 vendors will have to support it too.
> 
> So it is piece of the firmware we'd have to deal with too.
> 
> Now xen is a whole another deal - it is purely a piece of software.

But the role of xen (in fact, including other virtual solution like lguest/kvm) is virtual 'platform', equal to native h/w 'platform'.

> 
> Now I keep wondering, why don't you guys simply create your own mcelog
> ring buffer and interface on the userspace tool side instead of
> hooking into lowlevel kernel stuff? I mean, the code is there, you
> simply have to copy it into arch/xen/ or whatever you have there. Why
> do you have to hook into arch/x86/ instead of doing your own stuff?
> 
>>> So, my suggestion is to copy the pieces you need and create your
>>> own xen version of /dev/mcelog and add it to dom0 so that there's
>>> no hooking into baremetal code and whenever a dom0 kernel is
>>> running, you can reroute the mcelog userspace tool to read
>>> /dev/xen_mcelog or whatever and not hook into the x86 versions.

That would make distro camp confusing -- i.e. SLES10/11 unifiedly use /dev/mcelog for both native and xen mcelog, w/ almost same dom0 mcelog logic as this patch.

>>> 
>>> 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.
>> 
>> You would have more screaming from the distro camp about removing
>> /dev/mcelog.
> 
> How do you know that? Don't you think that we probably would've talked
> to them already and made preparations for conversion first?

I guess Novell Suse doubt this.

Thanks,
Jinsong--
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