A hypervisor provides a guest operating system with a plurality of protection domains, including a root protection domain and one or more secure protection domains, and mechanisms for controlling the transitions between the protection domains. The guest physical memory region of a secure protection domain, which is mapped to host physical memory by secure nested page tables, stores secure guest code and data, and guest page tables for the secure guest code. When executing secure guest code, the guest page tables stored in the secure protection domain region are used for guest virtual to guest physical address translations, and the secure nested page tables are used for guest physical to host physical address translations.