linux-kernel - Re: [PATCH v5 00/12] x86/microcode: Early load microcode

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Date:	Tue, 8 Jan 2013 14:46:34 -0500
From:	Konrad Rzeszutek Wilk <konrad@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Fenghua Yu <fenghua.yu@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Tigran Aivazian <tigran@...azian.fsnet.co.uk>,
	Yinghai Lu <yinghai@...nel.org>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Borislav Petkov <borislav.petkov@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v5 00/12] x86/microcode: Early load microcode

On Thu, Jan 03, 2013 at 09:48:43AM -0800, H. Peter Anvin wrote:
> On 01/03/2013 09:44 AM, Konrad Rzeszutek Wilk wrote:
> >
> >A couple of questions - why the usage of native_[read|write]_msr? I get the
> >__native_cpuid variant, but I am not sure I understand why you are using
> >the native_* variants. Especially as this code ends up being called on
> >Xen and lguest (at least on 64-bit) and probably should go through the
> >paravirt interfaces.
> >
> 
> For Xen, the early microcode update should be done in the hypervisor launch.

Right. That is the plan.
> 
> However, if you have a more specific flow in mind please clarify.

> Keep in mind Xen is largely a black box to non-Xen developers
> (#include <stdrant.h>).

OK. I am trying to figure out whether this usage of native_* for the
MSRs was done on purpose - and it sounds like the answer is no. If so -
can it be done using the normal 'safe_rdmsr' and 'wrmsr'?

That would allow at least in the case of Xen, to omit a whole bunch
of MSR writes/reads during the boot that are not neccessary as we would
not trap in the hypervisor - but could use the pvops version of
read/write MSR calls to just do a nop.

> 
> 	-hpa
> 
> P.S. Since when is lguest 64-bit?  Did I miss something?

Oh, I assumed it could do it.
> 
> -- 
> H. Peter Anvin, Intel Open Source Technology Center
> I work for Intel.  I don't speak on their behalf.
> 
> --
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