Comment # 1 on bug 1225968 from Ivan Topolsky

On EndeavourOS, gmhh has a similar outcome (running on 1 core only) with a very
similar setup.

https://forum.endeavouros.com/t/linux-6-9-seems-stuck-on-one-core/55979/14

Machine:
Type: Desktop Mobo: Gigabyte model: GA-970A-UD3 serial:
BIOS: Award v: F8f date: 12/16/2013
CPU:
Info: 6-core model: AMD FX-6300 bits: 64 type: MT MCP cache: L2: 6 MiB
Speed (MHz): avg: 1400 min/max: 1400/3500 cores: 1: 1400 2: 1400 3: 1400
4: 1400 5: 1400 6: 1400

(CPU is same Piledriver family, motherboard is same era and could potentially
be another "Hybrid EFI" firmware).

Seems that this problem is specific to the kernel, not the distro.
And happens when initialising additional core of Bulldozer/Piledriver gen AMD
CPUs.
(Potentially on BIOS-based motherboard?)