Timer offsetting mechanism in a virtual machine environment

• US 20060130059A1
• Filed: 10/29/2004
• Published: 06/15/2006
• Est. Priority Date: 10/29/2004
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Anderson, Andrew V., Neiger, Gilbert, Bennett, Steven M.
• Granted Patent: US 8,146,078 B2
• Time in Patent Office: Days
• US Class Current: 718/1
• CPC Class Codes: G06F 9/45533 Hypervisors; Virtual machine monitors

Abstract

In one embodiment, a method includes receiving a request to transition control to a virtual machine (VM) from a virtual machine monitor (VMM), calculating an offset value, receiving, during operation of the VM, a request for a current value of the timer, adjusting the current value of the timer based on the offset value, and providing the adjusted timer value to the VM.

Claims

1. A method comprising:

receiving a request to transition control to a virtual machine (VM) from a virtual machine monitor (VMM);

calculating an offset value;

receiving, during operation of the VM, a request for a current value of a timer;

adjusting the current value of the timer based on the offset value; and

providing the adjusted timer value to the VM.

2. The method of claim 1 further comprising:

transitioning control to the VM upon receiving the request from the VMM, the transitioning comprising calculating the offset value.

3. The method of claim 1 wherein calculating the offset value comprises:

determining a difference between a timer value read upon receiving the request to transition control to the VM and a timer value saved upon detecting a prior event associated with a transition of control from the VM to the VMM; and

subtracting the difference from a value of a timer offset field.

4. The method of claim 3 further comprising storing the calculated timer offset value to the timer offset field.

5. The method of claim 3 further comprising:

determining that an adjust timer offset indicator is set to an enabled value prior to determining the difference.

6. The method of claim 1 further comprising:

determining that an adjust timer offset indicator is set to a disabled value; and

reading a timer offset field, a value of the timer offset field being subsequently used as the offset value.

7. The method of claim 3 wherein the timer value is saved upon detecting the prior event associated with the transition of control to the VMM if a save timer indicator is enabled.

8. The method of claim 1 further comprising:

determining that a timer access control indicator is set to an exit value; and

transitioning control to the VMM in response to the request.

9. The method of claim 1 further comprising:

determining that offsetting of the timer is disabled; and

loading an offset register with zero.

10. An apparatus comprising:

a virtual machine monitor (VMM);

a data structure controlled by the VMM, the data structure storing an offset value for a virtual machine (VM); and

timer access logic to calculate the offset value upon receiving a request to transition control to the VM from the VMM, and to provide a value of the timer to the VM during an operation of the VM, the value of the timer being adjusted based on the offset value.

11. The apparatus of claim 10 wherein the timer access logic is further to transition control to the VM upon receiving the request from the VMM, the transitioning comprising calculating the offset value.

12. The apparatus of claim 10 wherein the timer access logic is to calculate the offset value by determining a difference between a timer value read upon receiving the request to transition control to the VM and a timer value saved upon detecting a prior event associated with a transition of control from the VM to the VMM, and subtracting the difference from a value of a timer offset field.

13. The apparatus of claim 12 wherein the data structure is further to include a timer offset field storing the calculated timer offset value.

14. The apparatus of claim 12 wherein the data structure is further to include an adjust timer offset indicator.

15. The apparatus of claim 14 wherein the timer access logic is further to determine that the adjust timer offset indicator is set to an enabled value prior to determining the difference.

16. The apparatus of claim 12 wherein the timer access logic is further to determine that an adjust timer offset indicator is set to a disabled value, and to read a timer offset field, a value of the timer offset field being subsequently used as the offset value.

17. The apparatus of claim 12 wherein the data structure is to store a save timer indicator used by the timer access logic to determine whether to save the timer value upon detecting the prior event associated with the transition of control to the VMM.

18. The apparatus of claim 10 further comprising:

an offset register to store the offset value.

19. A system comprising:

a memory to store a set of fields associated with timer offsetting for a virtual machine (VM); and

a processor, coupled to the memory, to use the set of fields associated with timer offsetting to calculate an offset value, and to provide, during operation of the VM, a timer value, adjusted based on the offset value, to the VM in response to a request of the VM for a current value of a timer.

20. The system of claim 19 wherein the processor is to calculate the offset value when transitioning control to the VM.

21. The system of claim 19 wherein the processor is further to load an offset register with the offset value.

22. The system of claim 19 wherein the processor is to calculate the offset value by determining a difference between a timer value read upon receiving the request to transition control to the VM and a timer value saved upon detecting a prior event associated with a transition of control from the VM to the VMM, and subtracting the difference from a value of a timer offset field.

23. The system of claim 22 wherein the processor is to read the timer value upon receiving the request to transition control to the VM if an adjust timer offset indicator is enabled.

24. The system of claim 22 wherein the processor is to save the timer value upon detecting the prior event associated with the transition of control to the VMM if a save timer indicator is enabled.

25. A machine-readable medium containing instructions which, when executed by a processing system, cause the processing system to perform a method, the method comprising:

receiving a request to transition control to a virtual machine (VM) from a virtual machine monitor (VMM);

calculating an offset value;

receiving, during operation of the VM, a request for a current value of a timer;

adjusting the current value of the timer based on the offset value; and

providing the adjusted timer value to the VM.

26. The machine-readable medium of claim 25 wherein the method further comprises:

transitioning control to the VM upon receiving the request from the VMM, the transitioning comprising calculating the offset value.

27. The machine-readable medium of claim 25 wherein calculating the offset value comprises:

determining a difference between a timer value read upon receiving the request to transition control to the VM and a timer value saved upon detecting a prior event associated with a transition of control from the VM to the VMM; and

subtracting the difference from a value of a timer offset field.

28. The machine-readable medium of claim 27 wherein the timer value is read upon receiving the request to transition control to the VM if an adjust timer offset indicator is enabled.

29. The machine-readable medium of claim 27 wherein the timer value is saved upon detecting the prior event associated with the transition of control to the VMM if a save timer indicator is enabled.