Memory segment emulation model for virtual machine
View Patent ↗A method of emulating segment addressing by a processor that includes initiating a Virtual Machine Monitor in a kernel mode; initiating a Virtual Machine in a user mode; forming a dynamically mapped table in Virtual Machine Monitor space, the dynamically mapped table corresponding to a table of segment descriptors of the Virtual Machine; populating the dynamically mapped table with descriptors that raise exceptions upon an attempt by the Virtual Machine to address a corresponding segment; and mapping a descriptor to the dynamically mapped table upon the Virtual Machine's use of that descriptor.
1. A system for managing memory in a computer running a Virtual Machine, the system comprising:
a host operating system having kernel mode privileges;
a Virtual Machine having user mode privileges and having a guest table identifying memory segments; and
a Virtual Machine Monitor having kernel mode privileges and that maintains a dynamically mapped table of pointers to segments identified by the guest table,
wherein the computer uses the dynamically mapped table to address Virtual Machine memory.
2. The system of claim 1 , wherein the Virtual Machine Monitor maintains a plurality of dynamically mapped tables of pointers, each table corresponding to a particular privilege level of the processor.
3. The system of claim 2 , wherein a segment virtualization model uses one set of tables and other dynamically mapped tables correspond to pointer mapping emulation model of segment-based memory addressing.
4. The system of claim 1 , wherein an exception handler is invoked to handle an attempt to use an unmapped pointer.
5. The system of claim 1 , wherein the dynamically mapped table is initialized with pointers that point to Not Present segments.
6. The system of claim 5 , wherein entries to the dynamically mapped table are added only when the Virtual Machine attempts to use a corresponding segment.
7. The system of claim 1 , entries to the dynamically mapped table are added only when the Virtual Machine attempts to use a corresponding segment.
8. The system of claim 1 , wherein the guest table includes a global descriptor table used by guest operating system code of the Virtual Machine, and a local descriptor used by user application code of the Virtual Machine, and wherein the dynamically mapped table includes a first corresponding table with dynamically mapped global descriptors and a second corresponding table with dynamically mapped local descriptors.
9. The system of claim 1 , wherein the Virtual Machine uses the local descriptor table for user application only, and the Virtual Machine's LDT can be loaded directly to the real processor.
10. The system of claim 1 , wherein the Virtual Machine's operations affecting segment registers are executed in a native mode.
11. The system of claim 1 , wherein the Virtual Machine's operations affecting the guest table are executed in a native mode.
12. The system of claim 1 , wherein the dynamically mapped table is mapped on a page-wise basis.
13. The system of claim 1 , wherein the pointers in the dynamically mapped table have no higher privilege than corresponding pointers in the guest table.
14. A method of emulating segment addressing by a processor, comprising:
initiating a Virtual Machine Monitor in a kernel mode;
initiating a Virtual Machine in a user mode;
forming a dynamically mapped table in Virtual Machine Monitor space, the dynamically mapped table corresponding to a table of segment descriptors of the Virtual Machine;
populating the dynamically mapped table with descriptors that raise exceptions upon an attempt by the Virtual Machine to address a corresponding segment; and
mapping a descriptor to the dynamically mapped table upon the Virtual Machine's use of that descriptor.
15. The method of claim 14 , wherein the Virtual Machine Monitor maintains a plurality of dynamically mapped tables of pointers, each table corresponding to a particular privilege level of the processor.
16. The method of claim 14 , wherein an exception handler is invoked to handle an attempt to use an unmapped pointer.
17. The method of claim 14 , wherein the dynamically mapped table is initialized with pointers that point to Not Present segments.
18. The method of claim 17 , wherein entries to the dynamically mapped table are added only when the Virtual Machine attempts to use a corresponding segment.
19. The method of claim 14 , wherein the guest table includes a global descriptor table used by guest operating system code of the Virtual Machine, and a local descriptor used by user application code of the Virtual Machine, and wherein the dynamically mapped table includes a first corresponding table with dynamically mapped global descriptors and a second corresponding table with dynamically mapped local descriptors.
20. The method of claim 14 , wherein the Virtual Machine's operations affecting segment registers are executed in a native mode.
21. The method of claim 14 , wherein the Virtual Machine's operations affecting the guest table are executed in a native mode.
22. The method of claim 14 , wherein the dynamically mapped table is mapped on a page-wise basis.
23. The method of claim 14 , wherein the pointers in the dynamically mapped table have no higher privilege than corresponding pointers in the guest table.