[CentOS] /lib/firmware/microcode.dat update on CentOS 6

Thu Jan 18 20:27:24 UTC 2018
Phil Perry <pperry at elrepo.org>

On 18/01/18 18:55, Matthew Miller wrote:
> On Thu, Jan 18, 2018 at 11:45:42AM -0500, Pete Geenhuizen wrote:
>>>> Do we update the microcode now or do we wait until the latest
>>>> microcode_ctl rpm is available and then tackle this issue?
>>> Check with your hardware vendor for BIOS/EFI firmware updates. Apply
>>> those.
>> Thanks for the reply, but you missed what I was asking.  I've
>> already downloaded the appropriate files from the links that Johnny
>> provided in a previous posting.
>> My question is, do we wait until the latest microcode_ctl rpm is
>> installed or do it now?  My concern is that if I do it now the new
>> rpm might undo what I've done.
> It does not matter. The microcode_ctl package contains CPU firmware
> that is loaded at by the kernel early in the boot process if it's newer
> than the one provided by the system firmware/BIOS. It is never
> permanently stored in NVRAM or anything — it's loaded at each boot.

Hence, by my understanding, there should not be any permanent damage 
should you get a 'bad' microcode update, either from Intel or Red Hat, 
that prevents the system from booting. Presumably one should still 
always be able to boot the machine from a rescue disk, mount the fs and 
either delete the offending microcode or uninstall the microcode_ctl 
package to allow the system to boot again. This should not result in a 
'bricked' permanently unrecoverable system.