Looks like AMD has already patched it, also appears to affect older Intel versions of the same tech concept but not current generations.
Only really affects guests in multi tenant hypervisor environments, requires physical access to the hypervisor, requires external physical hardware, requires booting the host with said hardware attached, at some point this level of compromise is already absurd. This kind of research is important and shows that we still need to limit out level of trust with host providers but I don't think anyone needs to panic.