Methods and apparatus for fast context switching in a virtualized system

Abstract

The present disclosure provides methods and apparatus for fast context switching in a. virtualized system. In the disclosed system, a globally unique application-space identifier is associated with each guest application. No two applications share the same application-space identifier, even if the two applications reside in different virtual machines. Domain identifiers are used to ensure that a guest's mappings are only active when that guest is executing. A unique domain identifier is associated with each virtual machine, and all translation lookaside buffer entries thereby mapping the guests kernel pages with that domain value. All other mappings are tagged with a predefined domain such as zero. In addition, a virtual memory management unit may be configured to support two virtual page table pointers and a configurable boundary between a virtual user page table and a virtual kernel page table. In such an instance, the two virtual page table pointers are presented to a guest operating system, and two physical page table pointers are associated with the two virtual page table pointers.

What is claimed is: 
     
         1 . A method of context switching in a virtualized system, the virtualized system having a plurality of globally unique domain identifiers, a plurality of different virtual machines, a plurality of translation lookaside buffer entries that control access to a memory, a plurality of globally unique application-space identifiers, a plurality of guest applications, and a domain access control register, the method comprising:
 associating a first domain identifier from the plurality of globally unique domain identifiers with a first virtual machine from the plurality of different virtual machines and associating a second domain identifier from the plurality of globally unique domain identifiers with a second virtual machine from the plurality of different virtual machines, wherein a third, predefined domain identifier from the plurality of globally unique domain identifiers is unassociated with any one virtual machine, wherein each domain identifier is different from every other domain identifier in the virtualized system, and wherein the domain access control register specifies whether translation lookaside buffer entries tagged with one of the domain identifiers are active;   associating the plurality of globally y unique application-space identifiers with the plurality of guest applications, wherein each application-space identifier is different from every other application-space identifier in the virtualized system, and wherein the plurality of guest applications reside in different virtual machines from the plurality of different virtual machines;   conditioned upon a virtual user mode being active, switching from the first virtual machine to the second virtual machine by loading the third, predefined domain identifier into the domain access control register; and   conditioned upon a virtual kernel mode being active, switching from the first virtual machine to the second virtual machine by loading the second domain identifier into the domain access control register.