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schard

Forum Moderator

From: Hannover

Registered: 2016-05-06

Posts: 1,964

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[SOLVED] Order of microcode when loading for multiple CPUs

I maintain a periodically updated root file system image of a customized Arch Linux installation for my company.
It is used for quick mass-duplication for digital signage deployment.
It was originally set up back in early 2015 according to the official installation guide and has been updated ever since.
The image is deployed on several different hardware.
Thusly, on AMD systems I need to load the AMD microcode and on Intel systems the Intel microcode.
The obvious solution would be to maintain two separate images for each CPU manufacturer.
Since this is not feasible, I had a look at how the live ISO addresses this issue, since it's expected to run on multiple different hardware configurations as well.
I noticed, that the live ISO first loads the Intel microcode, then the AMD microcode.
My question is: Is this order random or on purpose. I.e. would things break, if I loaded the AMD microcode first and then the Intel microcode?
A first test of this did not yield any issues with the reversed order.
But I'd like to know whether I could run into any troubles with the order or even break the CPUs when the "wrong" microcode is loaded.
Soluion: Since after a week of testing, nothing bad happend, I assume, that the order of the Microcodes is irrelevant.

Last edited by schard (2019-09-09 08:13:00)

frostschutz

Member

Registered: 2013-11-15

Posts: 1,417

Re: [SOLVED] Order of microcode when loading for multiple CPUs

loading the wrong microcode should be impossible (except "wrong" as in older microcode for the same cpu model ... it's an older code, sir, but it checks out...)

also kernel should load it by itself (early microcode)

edit:

hmmm, if https://www.kernel.org/doc/Documentatio … rocode.txt is still correct it might be the early load only works for a single cpu type

otherwise you have to use the late load method as explained there (but it also does not differentiate between intel or amd) or the builtin firmware as a custom kernel build

you don't use the userspace tool anymore

Last edited by frostschutz (2019-08-30 08:15:06)