The focus of many in high-assurance security after 90's maybe was that using compromised OS's or hypervisor's maintaining security properties is best done with a hardware architecture that does the crypto at CPU level on individual processes, pages, and so on with the chip being the trust boundary. They've spent a while trying to improve on security and performance. Edmison's design was last one I saw that I liked with great section on prior work:

https://theses.lib.vt.edu/theses/available/etd-10112006-2048...