1. A method of isolating secure guest code to be executed in a guest that is configured in a host by a virtualization software, comprising: creating first page tables, which are used for guest physical to host physical address translations, that provide mappings to a first protected region of host physical memory where the secure guest code has been loaded; creating second page tables, which are used for guest physical to host physical address translations, that provide mappings to a second protected region of the host physical memory; storing third page tables, which are used for guest virtual to guest physical address translations, in the first protected region; storing fourth page tables, which are used for guest virtual to guest physical address translations, in the second protected region; and when execution is switched from a non-secure guest code, which is loaded into the second protected region, to the secure guest code, changing a first pointer value from one that points to the fourth page tables to one that points to the third page tables so that the third page tables are accessed for guest virtual to guest physical address translations, and changing a second pointer value from one that points to the second page tables to one that points to the first page tables so that the first page tables are accessed for guest physical to host physical address translations.