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[Xen-devel] Re: [PATCH 0/3] x86/microcode: support for microcode update

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 0/3] x86/microcode: support for microcode update in Xen dom0
From: "H. Peter Anvin" <hpa@xxxxxxxxx>
Date: Wed, 12 Oct 2011 14:31:50 -0700
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Tigran Aivazian <tigran@xxxxxxxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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On 10/12/2011 01:40 PM, Konrad Rzeszutek Wilk wrote:
Why is it paramount to do it as early as possible? As in, even doing
it before Linux kernel is invoked is preferred than during initrd runtime?

It is paramount to do it as early as possible *because the CPU is broken*. That's why there is a microcode update at all. It is *supposed* to be installed by BIOS, but for whatever reason it wasn't (including user doesn't want to update the BIOS), so the very fact that this is done in the OS at all is a bit of a fail.

Doing it in the bootloader is messy because bootloaders typically aren't SMP-aware (and really shouldn't need to be), which leaves the OS. On native hardware it should ideally be done as early in the processor bringup as possible.

        -hpa

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