linux-kernel - Re: [Xen-devel] [PATCH 1/3] xen/mce: Add mcelog support for Xen platform (v2)

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Date:	Fri, 25 May 2012 14:01:02 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"Liu, Jinsong" <jinsong.liu@...el.com>
Cc:	Borislav Petkov <bp@...64.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [Xen-devel] [PATCH 1/3] xen/mce: Add mcelog support for Xen
 platform (v2)

On Fri, May 25, 2012 at 05:56:56PM +0000, Liu, Jinsong wrote:
> Konrad Rzeszutek Wilk wrote:
> >>>>>> -static struct miscdevice mce_chrdev_device = {
> >>>>>> +struct miscdevice mce_chrdev_device = {
> >>>>>>  	MISC_MCELOG_MINOR,
> >>>>>>  	"mcelog",
> >>>>>>  	&mce_chrdev_ops,
> >>>>> 
> >>>>> You're still reusing those - pls, define your own 'struct
> >>>>> miscdevice mce_chrdev_device' in drivers/xen/ or somewhere
> >>>>> convenient and 
> >>>>> your own mce_chrdev_ops. The only thing you should be touching in
> >>>>> arch/x86/.../mcheck/ is the export of MISC_MCELOG_MINOR.
> >>>>> 
> >>>>> Thanks.
> >>>> 
> >>>> I'm *not* reuse native code.
> >>>> I have defined 'struct miscdevice xen_mce_chrdev_device' in
> >>>> drivers/xen, and I also implement xen_mce_chrdev_ops, they are all
> >>>> xen-self-contained. 
> >>>> 
> >>>> The patch just redirect native mce_chrdev_device to
> >>>> xen_mce_chrdev_device when running under xen environment.
> >>>> It didn't change any native code (except just cancel
> >>>> mce_chrdev_device 'static'), and will not break native logic.
> >>> 
> >>> Why are you doing that?
> >>> 
> >>> Why don't you do
> >>> 
> >>> 	misc_register(&xen_mce_chrdev_device);
> >>> 
> >>> in xen_early_init_mcelog() ?
> >>> 
> >>> This way there'll be no arch/x86/ dependencies at all.
> >> 
> >> The reason is, if we do so, it would be covered by native
> >> misc_register(&mce_chrdev_device) later when native kernel init (xen
> >> init first and then start native kernel).  
> > 
> > Won't the second registration (so the original one) of the major
> > fail? So the mce_log would just error out since somebody already
> > registered? 
> 
> No, that would be device confliction, the 2nd register return as -EBUSY and un-predicetable result.

And the existing code does not actually check the 'misc_register' return
value? Ah yes. Perhaps then a fix to arch/x86/kernel/cpu/mcheck/mce.c to
do the proper de-registration if 'misc_register' fails?

Or just set 'mce_disabled=1' in the bootup of Xen, similar to
how lguest.c does it?

> I test it in your way, mcelog fail to fetch any error log.

And that is b/c of? What exactly?
> 
> Thanks,
> Jinsong
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