Virtualization with Multiple Shadow Page Tables

• US 20130283004A1
• Filed: 06/07/2013
• Published: 10/24/2013
• Est. Priority Date: 05/30/2008
• Status: Active Grant

• Current Assignee: Vmware LLC (Broadcom, Inc.)
• Original Assignee: VMware, Inc. (Broadcom, Inc.)
• Inventors: Devine, Scott W., Rogel, Lawrence S., Fry, Gerald A., Bungale, Prashanth P.
• Granted Patent: US 8,868,880 B2
• Time in Patent Office: Days
• US Class Current: 711/206
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/06 Addressing a physical block of locations, e.g. base addressing, module addressing, memory dedication G06F12/08 takes precedence
• CPC Class Codes: G06F 12/08 in hierarchically structured memory systems, e.g. virtual memory systems
• CPC Class Codes: G06F 12/10 Address translation
• CPC Class Codes: G06F 12/1009 using page tables, e.g. page table structures
• CPC Class Codes: G06F 12/1036 for multiple virtual address spaces, e.g. segmentation G06F12/1045 takes precedence
• CPC Class Codes: G06F 12/109 for multiple virtual address spaces, e.g. segmentation G06F12/1036 takes precedence
• CPC Class Codes: G06F 2212/151 Emulated environment, e.g. virtual machine
• CPC Class Codes: G06F 2212/152 Virtualized environment, e.g. logically partitioned system
• CPC Class Codes: G06F 8/40 Transformation of program code
• CPC Class Codes: G06F 9/455 Emulation; Interpretation; Software simulation, e.g. virtualisation or emulation of application or operating system execution engines
• CPC Class Codes: G06F 9/54 Interprogram communication

Abstract

A computing system includes virtualization software including a guest operating system (OS). A method maintains, by the virtualization software layer, a first shadow page table for use in a kernel mode and a second shadow page table for use in a user mode. The virtualization software switches between using the first shadow page table and the second shadow page table when the guest OS switches between operating in the kernel mode and the user mode.

Claims

1. A method for operating in a computing system comprised of virtualization software including a guest operating system (OS), the method comprising:

maintaining, by the virtualization software layer, a first shadow page table for use in a kernel mode;

maintaining, by the virtualization software layer, a second shadow page table for use in a user mode; and

switching, by the virtualization software, between using the first shadow page table and the second shadow page table when the guest OS switches between operating in the kernel mode and the user mode.

3. The method of claim 1 further comprising:

receiving a user mode guest OS instruction; and

using the second shadow page table to process the user mode guest OS instruction.

2. The method of 1 further comprising:

receiving a kernel mode guest OS instruction; and

using the first shadow page table to process the kernel mode guest OS instruction.

4. The method of 1 wherein the first shadow page table maintains entries only valid in the kernel mode and the second shadow page table maintains entries only valid in the user mode. /

5. The method of 1 further comprising:

marking guest OS pages having all user mode guest OS instructions as user mode pages;

marking guest OS pages having kernel mode guest OS instructions as kernel mode pages; and

marking all pages in virtualization software address space as kernel mode pages, wherein the first shadow page table is maintained for the kernel mode pages and the second shadow page table is maintained for the user mode pages.

6. The method of 1 further comprising:

changing kernel mode guest OS load or store instructions to load “

as user”

or store “

as user”

instructions;

trapping accesses by the guest OS of kernel mode guest OS instructions;

switching from the first shadow page table to the second shadow page table; and

emulating and returning a value expected by the guest OS using the second shadow page table.

7. The method of 6 wherein changing comprises:

setting an “

S”

bit in each of the load or store instructions to indicate that the load or store instruction should be executed in the user mode.

8. The method of 1 further comprising:

treating a virtualization software layer load or store instruction as a normal load or store, respectively; and

returning a value using the first shadow page table for the virtualization software layer load or store instruction.

9. A non-transitory computer-readable storage medium containing instructions for operating in a computing system comprised of virtualization software including a guest operating system (OS), the instructions, when executed, control the computer system to be configured for:

maintaining, by the virtualization software layer, a first shadow page table for use in a kernel mode;

maintaining, by the virtualization software layer, a second shadow page table for use in a user mode; and

switching, by the virtualization software, between using the first shadow page table and the second shadow page table when the guest OS switches between operating in the kernel mode and the user mode.

10. The non-transitory computer-readable storage medium of 9 further comprising:

receiving a kernel mode guest OS instruction; and

using the first shadow page table to process the kernel mode guest OS instruction.

11. The non-transitory computer-readable storage medium of 9 further comprising:

receiving a user mode guest OS instruction; and

using the second shadow page table to process the user mode guest OS instruction.

12. The non-transitory computer-readable storage medium of 9 wherein the first shadow page table maintains entries only valid in the kernel mode and the second shadow page table maintains entries only valid in the user mode.

13. The non-transitory computer-readable storage medium of 9 further comprising:

marking guest OS pages having all user mode guest OS instructions as user mode pages;

marking guest OS pages having kernel mode guest OS instructions as kernel mode pages; and

marking all pages in virtualization software address space as kernel mode pages, wherein the first shadow page table is maintained for the kernel mode pages and the second shadow page table is maintained for the user mode pages.

14. The non-transitory computer-readable storage medium of 9 further comprising:

changing kernel mode guest OS load or store instructions to load “

as user”

or store “

as user”

instructions;

trapping accesses by the guest OS of kernel mode guest OS instructions;

switching from the first shadow page table to the second shadow page table; and

emulating and returning a value expected by the guest OS using the second shadow page table.

15. The non-transitory computer-readable storage medium of 14 wherein changing comprises:

setting an “

S”

bit in each of the load or store instructions to indicate that the load or store instruction should be executed in the user mode.

16. The non-transitory computer-readable storage medium of 9 further comprising:

treating a virtualization software layer load or store instruction as a normal load or store, respectively; and

returning a value using the first shadow page table for the virtualization software layer load or store instruction.

17. An apparatus comprised of virtualization software including a guest operating system (OS), the apparatus comprising:

one or more computer processors; and

a non-transitory computer-readable storage medium comprising instructions, that when executed, control the one or more computer processors to be configured for;

maintaining, by the virtualization software layer, a first shadow page table for use in a kernel mode;

maintaining, by the virtualization software layer, a second shadow page table for use in a user mode; and

switching, by the virtualization software, between using the first shadow page table and the second shadow page table when the guest OS switches between operating in the kernel mode and the user mode.

18. The apparatus of 17 further configured for:

receiving a kernel mode guest OS instruction; and

using the first shadow page table to process the kernel mode guest OS instruction.

19. The apparatus of 17 further comprising:

receiving a user mode guest OS instruction; and

using the second shadow page table to process the user mode guest OS instruction.

20. The apparatus of 17 wherein the first shadow page table maintains entries only valid in the kernel mode and the second shadow page table maintains entries only valid in the user mode.