It's not clear, but with the latest AGESA all AMD Zen and later CPUs should be fine. Which firmware first contained the fix? I don't know, at least not without digging for further details. I assume quite a few 300-series chipset motherboards are still going to be limited to older firmware, but this isn't a massive problem anyway since it requires administrative (and?) or physical access to the system. If that has happened, you should already assume the PC is compromised.