[Xen-devel] Re: [PATCH 0/3] x86/microcode: support for microcode update in Xen dom0

["H. Peter Anvin" <hpa@xxxxxxxxx>]

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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