This, like also some reverse engineering of the CPU microcode that has been discussed previously on HN, is supported only on certain Intel Atom CPUs with Goldmont cores, i.e. Apollo Lake, Gemini Lake, maybe also Denverton.

The reason is that only for these cores there is a known exploit that can switch the CPU of any computer with this kind of core into a debugging mode that gives access to the microcode.

Similar debugging modes certainly exist on all Intel and AMD CPUs, but there is no public knowledge about how they can be activated and no known bugs that enable that. Moreover, this debugging mode is normally disabled on the PCB in production motherboards. So even for someone who would know how to do it for other kinds of Intel cores or for AMD, it is expected that physical access to the motherboard is needed, to make modifications on the PCB.

While this new information about the internals of the Intel Goldmont cores is very interesting, it does not increase the chances of any similar hacking of the other more modern Intel cores.

It is likely that Intel will be more careful in the future to avoid such a reverse engineering of the microcode and of the debugging mode, even if that does not really matter much, either for security or for competitors.

There has been some older work on reversing AMD K8 and K10 that lets you do something vaguely similar. This work is just way more generalized, with more options available in the Intel way of things. https://www.usenix.org/conference/usenixsecurity17/technical...

Seems like you can't really trace the AMD CPUs like the reversing of that Intel Microcode allows, but you can still do a lot.