linux-kernel - Re: [PATCH 0/2] x86/microcode: support for microcode update in Xen dom0

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Date:	Thu, 3 Feb 2011 19:25:50 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>, Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen Devel <Xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 0/2] x86/microcode: support for microcode update in Xen
 dom0

On Wed, Feb 02, 2011 at 01:47:18PM -0800, H. Peter Anvin wrote:
> On 02/02/2011 12:57 PM, Borislav Petkov wrote:
> > On Wed, Feb 02, 2011 at 11:52:22AM -0800, H. Peter Anvin wrote:
> >> 3. Arguably on native hardware we should still load the microcode into
> >> RAM in the boot loader, and install it on the very early CPU bringup
> >> path.  That means locking down some (currently) 400K of RAM to handle
> >> different combinations of CPUs, or the additional complexity of
> >> jettisoning microcode which cannot be used while still be able to deal
> >> with hotplug.  I think there is a strong case for this model, which
> >> would mean moving the microcode into /boot anyway.
> > 
> > /me like it, sounds very nifty. So how do we want to do that, we add
> > a field to the real-mode kernel header that tells us where to find
> > the microcode image and we take it and apply the ucode somewhere in
> > do_boot_cpu() path?
> > 
> 
> We already have a mechanism for passing arbitrary blobs -- the linked
> list -- so we don't have to add a new field at all.

So, after staring at grub legacy sources a bit, we could load the
microcode image using the grub module's mechanism:

kernel /...
module /boot/microcode.gz type=SETUP_MICROCODE # this is looked at by parse_setup_data()

and let grub write the pointer into setup_data passed through the kernel
header.

This would mean that we need to add support to a bunch of boot loaders
used currently, no? Or is there an even better way?

-- 
Regards/Gruss,
Boris.
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