AMDSEV/SME or Intel SGX/TME/MKTME or whatever other HW encrypted page support exist are buggy, which cannot be patched. E.g. AsyncShock

https://github.com/vschiavoni/sgx-papers

This is a SW-only solution, and therefore is probably also buggy, but can be patched and only accessed via ring < 0. Only via yet unknown kernel bugs (patchable) or the mythical ME or ASP/PSP backdoors.

https://semiaccurate.com/2017/06/22/amds-epyc-major-advance-...