I am interested in Zephyr SMP support for the Arm M class of microcontrollers . It’s not clear from the Zephyr SMP documentation  which architectures Zephyr currently supports, but I’ve gathered from other links that ARC, RISC-V and ARM A class are supported – possibly others as well.
According to a thread on this list back in October of 2020 , “to fully implement SMP you'll need per-cpu variables, IPIs, some extra arch_* APIs implemented, etc.”
It sounds like a porting guide did not exist back then. Is there by chance now a porting guide for SMP that I could follow? If not, could somebody provide a little more guidance as to how to get started?