Abstract: A computing device includes a memory and a processor. The memory is to store software. The processor is to receive an In-Service Software Downgrade (ISSD) request to downgrade the software from a high version to a low version. Responsively to the ISSD request, the processor is to identify one or more high-version-only software features that (i) are supported by the high version and not supported by the low version, and (ii) write one or more new values into one or more registers in a Control Register Space (CR-Space) of the processor, and to allow downgrading of the software only in response to verifying that the new values meet a defined downgradability criterion.