Shadow page tables for address translation control

In a computer system that employs virtual memory, multiple versions of a given page are stored: a directory version, a table version, and a data version. The data version contains the data that a software object believes to be stored in the page. The directory and table versions of the page contains versions of the page's contents that have been modified in some manner to comply with a restriction on the address translation map employed by the virtual address system. When a page is being used by the virtual address system as a directory or table, then the directory or table versions, respectively, of that page are used. When a page is the target of a read request, the data version of the page is used.