Switching between multiple software entities using different operating modes of a processor in a computer system

• US 7,478,388 B1
• Filed: 04/21/2004
• Issued: 01/13/2009
• Est. Priority Date: 04/21/2004
• Status: Active Grant

• Current Assignee: Vmware LLC (Broadcom, Inc.)
• Original Assignee: VMware, Inc. (Broadcom, Inc.)
• Inventors: Manchester, Robert D., Munoz, Alberto J., Chen, Xiaoxin, Rihan, Sahil
• Primary Examiner(s): An; Meng-Ai
• Assistant Examiner(s): WAI, ERIC CHARLES
• Application Number:
  US10/829,780
• Time in Patent Office: 1,728 Days
• Field of Search: 718/1
• US Class Current: 718/1
• CPC Class Codes: G06F 9/45554 Instruction set architectures of guest OS and hypervisor or native processor differ, e.g. Bochs or VirtualPC on PowerPC MacOS

Abstract

A processor has multiple operating modes, such as the long/compatibility mode, the long/64-bit mode and the legacy modes of the x86-64 microprocessor. Different software entities execute in different ones of these operating modes. A switching routine is implemented to switch from one operating mode to another and to transfer control from one software entity to another. The software entities may be, for example, a host operating system and a virtual machine monitor. Thus, for example, a virtual computer system may comprise a 64-bit host operating system and a 32-bit virtual machine monitor, executing on an x86-64 microprocessor in long mode and legacy mode, respectively, with the virtual machine monitor supporting an x86 virtual machine. The switching routine may be implemented partially or completely in an identity-mapped memory page. Execution of the switching routine may be initiated by a driver that is installed in the host operating system of a virtual computer system.

Claims

1. A computer program embodied in a tangible medium, the computer program being executable in a computer system, the computer system comprising a new processor having a new operating mode and a legacy operating mode, the legacy operating mode being suitable for executing a legacy application and a legacy operating system (OS), the computer system further comprising a host OS that is executable on the new processor in the new operating mode, the computer program comprising:

a virtualization software that is executable on the new processor in the legacy mode, the virtualization software supporting a virtual machine (VM) having a virtual legacy processor on which a legacy OS and a legacy application can run;

a switch routine for switching between the host OS executing in the new operating mode and the virtualization software executing in the legacy operating mode, the new processor including a legacy instruction set for the legacy operating mode and a new instruction set for the new operation mode, the switching includes switching from the new instruction set to the legacy instruction set and switching paging tables, each of the new operating mode and the legacy operating mode having separate paging tables,

wherein, the switch routine is incorporated in a switch page that is locked in physical memory, the switch page having a first section to store a part of switching instructions conforming to the new instruction set and a second section to store another part of the switching instructions conforming to the legacy instruction set; and

a driver loaded in the host OS for initiating the switch routine from the host OS, wherein the switch routine is a part of the driver.

2. The computer program of claim 1, further comprising a host application executing on the host OS, the host application being schedulable by the host OS and calling into the driver to initiate the switch routine.

3. The computer program of claim 2, wherein the processor also has a compatibility mode that is suitable for executing a legacy application on an OS that is executable on the new processor in the new operating mode, and wherein the host application is a legacy application executing in the compatibility mode.

4. The computer program of claim 2, wherein the driver and the host application are also used to enable the virtualization software to use the host OS to access a physical device.

5. The computer program of claim 1, further comprising a switch page table that contains first identity mapping that is used when disabling memory paging when switching between the new operating mode and the legacy operating mode.

6. The computer program of claim 1, wherein the new processor is an x86-64 processor, the host OS is a 64-bit OS, the virtual software is a 32-bit virtual machine monitor and the virtual legacy processor in the VM is a virtual x86 processor.

7. The computer program of claim 5, further comprising a second identity mapping that is loaded into a page table of the virtualization software.

8. The computer program of claim 5, further comprising a switch segment descriptor table that is used when switching between the new operating mode and the legacy operating mode.

9. The computer program of claim 1, wherein the switch routine comprises a switch page that contains a first portion of code that is executable in the new operating mode and a second portion of code that is executable in the legacy operating mode.

10. The computer program of claim 9, wherein the first portion of code and the second portion of code are contained in contiguous physical memory on the switch page.

11. A method for switching from a first software entity executing in a 64-bit mode of an x86-64 processor to a second software entity executing in a legacy mode of the processor, the first and second software entities both running at the same system level of the processor, the first software entity and the second software entity each executing with memory paging enabled, the first software entity using a first page table, the second software entity using a second page table, the method comprising:

a) activating a switch page table, the switch page table being different from the first and second page tables, the switch page table including a first identity mapping for a switch page, wherein the switch page includes a switch code section and a switch data section, the switch code section includes instructions for performing a context switch and the switch data section includes instructions to perform a switch between the first software entity and the second software entity, a part of the instructions for performing the switch being compiled to work in a long mode of the x86-64 processor;

b) switching to a compatibility mode of the processor;

c) switching to fetch instructions from the switch page using the first identity mapping;

d) disabling memory paging, wherein disabling memory paging causes the processor to switch to the legacy mode;

e) disabling the long mode of the processor;

f) activating the second page table, the second page table including a second identity mapping for the switch page;

g) enabling memory paging; and

h) loading a plurality of registers of the processor with values for the second software entity, to restore a context of the second software entity.

12. The method of claim 11, wherein the steps a), b), c), d), e), f), g) and h) are performed sequentially, in alphabetical order.

13. The method of claim 11, further comprising, before the step a), saving the plurality of registers of the processor to save a context of the first software entity.

14. The method of claim 11, further comprising, after the step h), replacing the second identity mapping in the second page table with a virtual address mapping of the second software entity.

15. The method of claim 11, wherein the first software entity is a host operating system and the second software entity is a virtual machine monitor in a virtual computer system.

16. The method of claim 11, wherein the steps b) and c) are performed by executing a long jump instruction, which loads a first code descriptor into a code segment register, the first code descriptor specifying a first code segment that includes the switch page.

17. The method of claim 16, further comprising, after the step a), activating a switch segment descriptor table and loading a first data descriptor into a data segment register, the first data descriptor specifying a first data segment that includes the switch page.

18. The method of claim 17, further comprising, after the step e), activating a segment descriptor table for the second software entity and, after the step g), loading a second data descriptor into the data segment register, the second data descriptor specifying a second data segment of the second software entity.

19. The method of claim 18, further comprising, after the step h), loading a second code descriptor into the code segment register, the second code descriptor specifying a second code segment of the second software entity.

20. The method of claim 11, wherein the step c) is performed before the step b).

21. A method for switching from a second software entity executing in a legacy mode of an x86-64 processor to a first software entity executing in a 64-bit mode of the processor, the first and second software entities both running at the same system level of the processor, the first software entity and the second software entity each executing with memory paging enabled, the first software entity using a first page table, the second software entity using a second page table, the method comprising:

a) switching to fetch instructions from a switch page using a second identity mapping for the switch page, the second identity mapping being in the second page table, wherein the switch page includes a switch code section and a switch data section, the switch code section includes instructions for performing a context switch and the switch data section includes instructions to perform a switch between the first software entity and the second software entity, a part of the instructions for performing the switch being compiled to work in the 64-bit mode of the x86-64 processor;

b) disabling memory paging;

c) activating a switch page table, the switch page table being different from the first and second page tables, the switch page table including a first identity mapping for the switch page, and continuing to fetch instructions from the switch page, but now using the first identity mapping;

d) enabling the long mode of the processor;

e) enabling memory paging, which causes the processor to switch to the compatibility mode;

f) switching to the 64-bit mode of the processor;

g) activating the first page table; and

h) loading a plurality of registers of the processor with values for the first software entity, to restore a context of the first software entity.

22. The method of claim 21, wherein the steps a), b), c), d), e), f), g) and h) are performed sequentially, in alphabetical order.

23. The method of claim 21, further comprising, before the step a), saving a virtual address mapping of the second software entity from the second page table, the virtual address mapping providing a mapping for a virtual page number that equals a physical page number of the switch page, and replacing the virtual address mapping in the second page table with the second identity mapping.

24. The method of claim 23, further comprising, before the step a), saving the plurality of registers of the processor to save a context of the second software entity.

25. The method of claim 21, wherein the first software entity is a host operating system and the second software entity is a virtual machine monitor in a virtual computer system.

26. The method of claim 21, further comprising, after the step a), activating a switch segment descriptor table and, after the step e), loading a first data descriptor into a data segment register, the first data descriptor specifying a first data segment that includes the switch page.

27. The method of claim 26, further comprising, after the step f), activating a segment descriptor table for the first software entity and, after the step g), loading a second data descriptor into the data segment register, the second data descriptor specifying a second data segment of the first software entity.

28. The method of claim 27, further comprising, after the step h), loading a code descriptor into a code segment register, the code descriptor specifying a code segment of the first software entity.

29. The method of claim 21, further comprising, after the step f), performing a jump instruction to a virtual address of the first software entity that maps to the switch page.

30. The method of claim 21, wherein the step c) is performed before the step b).

31. A computer program embodied in a tangible medium, the computer program being executable in a computer system, the computer system comprising a new processor having a new operating mode and a legacy operating mode, the legacy operating mode being suitable for executing a legacy application and a legacy operating system (OS), the computer system further comprising a host OS that is executable on the new processor in the new operating mode, the computer program comprising:

a virtualization software that is executable on the new processor in the legacy mode, the virtualization software supporting a virtual machine (VM) having a virtual legacy processor on which a legacy OS and a legacy application can run;

a switch routine for switching between the host OS executing in the new operating mode and the virtualization software executing in the legacy operating mode, the new processor including a legacy instruction set for the legacy operating mode and a new instruction set for the new operation mode, the switching includes switching from the new instruction set to the legacy instruction set and switching paging tables, each of the new operating mode and the legacy operating mode having separate paging tables,

wherein, the switch routine is incorporated in a switch page that is locked in physical memory, the switch page having a first section to store a part of switching instructions conforming to the new instruction set and a second section to store another part of the switching instructions conforming to the legacy instruction set; and

a driver loaded in the host OS and a host application executing on the host OS, the host application being schedulable by the host OS and calling into the driver to initiate the switch routine.

32. The computer program of claim 31, wherein the processor also has a compatibility mode that is suitable for executing a legacy application on an OS that is executable on the new processor in the new operating mode, and wherein the host application is a legacy application executing in the compatibility mode.

33. The computer program of claim 31, wherein the driver and the host application are also used to enable the virtualization software to use the host OS to access a physical device.