linux-kernel - RE: [Xen-devel] v3.9 - CPU hotplug and microcode earlier loading hits a mutex deadlock (x86_cpu_hotplug_driver

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Message-ID: <92B37F2487AE0841841737618F25AC1A0FF5B3B4@FTLPEX01CL03.citrite.net>
Date:	Wed, 8 May 2013 15:41:49 +0000
From:	Ross Philipson <Ross.Philipson@...rix.com>
To:	Borislav Petkov <bp@...en8.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"fenghua.yu@...el.com" <fenghua.yu@...el.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: RE: [Xen-devel] v3.9 - CPU hotplug and microcode earlier loading
 hits a mutex deadlock (x86_cpu_hotplug_driver_mutex)

> -----Original Message-----
> From: xen-devel-bounces@...ts.xen.org [mailto:xen-devel-
> bounces@...ts.xen.org] On Behalf Of Borislav Petkov
> Sent: Wednesday, May 08, 2013 7:30 AM
> To: Konrad Rzeszutek Wilk
> Cc: fenghua.yu@...el.com; xen-devel@...ts.xensource.com; x86@...nel.org;
> linux-kernel@...r.kernel.org; mingo@...hat.com; hpa@...or.com;
> tglx@...utronix.de
> Subject: Re: [Xen-devel] v3.9 - CPU hotplug and microcode earlier
> loading hits a mutex deadlock (x86_cpu_hotplug_driver_mutex)
> 
> On Wed, May 08, 2013 at 10:03:42AM -0400, Konrad Rzeszutek Wilk wrote:
> 
> [ … snip some funky BIOS code ]
> 
> > [here it shifts and continues on testing each CPU bit]
> >
> > > Questions over questions...?
> >
> > I probably went overboard with my answers :-)
> 
> Konrad, you're killing me! :-) You actually went and looked at the
> BIOS disassembly voluntarily. You must be insane, I think you should
> immediately go to the doctor now for a thorough checkup. :-)
> 
> I think I know who I can sling BIOS issues now to.
> 
> > > Looks like save_mc_for_early would need another, local mutex to fix
> that.
> >
> > Let me try that. Thanks for the suggestion.
> 
> Ok, seriously now: yeah, this was just an idea, it should at least get
> the nesting out of the way.
> 
> About the BIOS deal: you're probably staring at some BIOS out there
> but is this the way that it is actually going to be implemented on
> the physical hotplug BIOS? I mean, I've only heard rumors about IVB
> supporting physical hotplug but do you even have access to such BIOS to
> verify?

The ASL Konrad traced through is to make the ACPI bits a guest
interoperate with qemu etc. On bare metal it will be much more opaque
and ugly; the processor related AML will probably burrow down into an
SMI to do the real work.

Ross
> 
> All I'm saying is, let's not hurry too much before we actually can
> really trigger this on baremetal.
> 
> Thanks.
> 
> --
> Regards/Gruss,
>     Boris.
> 
> Sent from a fat crate under my desk. Formatting is fine.
> --
> 
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