Abstract: In a system for implementing virtual machines a Virtual Machine Monitor (VMM) is assigned an address space separate and distinct from the address space assigned to the virtual machines (VMs). A VM-bit is used to determine whether the processor is executing a process in the VM or the VMM. Through the use of the separate address spaces and the VM-bit a system is disclosed wherein the VMM can take full advantage of all the protection rings offered by the system on which it runs and the VMs are also allowed to operate in an environment that essentially offers the same number of real protection rings as are available on the underlying computer system.

Abstract: A central processing unit (CPU) executing a virtual memory management system employs a translation buffer for caching recently used page table entries. When more than one process is executing on the CPU, the translation buffer is usually flushed when a context switch is made, even though some of the entries would still be valid for commonly-referenced memory areas. An address space number feature is employed to allow entries to remain in the translation buffer for processes not currently executing, and the separate processes or the operating system can reuse entries in the translation buffer for such pages of memory that are commonly referenced. To allow this, an "address space match" entry in the page table entry signals that the translation buffer content can be used when the address tag matches, even though the address space numbers do not necessarily match.