linux-kernel - Re: Linux* Processor Microcode Data File

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Date:	Mon, 9 Mar 2009 18:00:35 +0800
From:	Jike Song <albcamus@...il.com>
To:	Dragoslav Zaric <dragoslav.zaric.kd@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Linux* Processor Microcode Data File

On Mon, Mar 9, 2009 at 5:43 PM, Dragoslav Zaric
<dragoslav.zaric.kd@...il.com> wrote:
> Hello,
>
> I was browsing Intel web site for my processor docs and I bumped
> on download link "Linux* Processor Microcode Data File" and it says
> there:
>
> "The microcode data file contains the latest microcode definitions for
> all Intel processors.
> Intel releases microcode updates to correct processor behavior as
> documented in the respective
> processor specification updates. While the regular approach to getting
> this microcode update is via
> a BIOS upgrade, Intel realizes that this can be an administrative
> hassle. The Linux Operating System
> and VMware ESX products have a mechanism to update the microcode after
> booting. For example,
> this file will be used by the operating system mechanism if the file
> is placed in the /etc/firmware
> directory of the Linux system."
>
> So, does new kernel versions just copy this microcode update file in
> /etc/firmware folder or new
> instructions are replaced in assembly code ?
>

Linux provides an microcode driver for Intel & AMD CPUs:

    arch/x86/kernel/microcode_*

and there is a service called "microcode_ctl" to open it and write the
microcode on every starting.   Where to find the microcode data is
this service specified, and the kernel doesn't care it.  You may want
to find:

http://www.urbanmyth.org/microcode/

> new  instructions are replaced in assembly code ?
As far as I can tell, no.   The microcode only only change the CPU's
behavior, not the assembler.


-- 
Thanks,
Jike
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