The document describes a virtual memory kernel and process for a virtual machine. The VMKernel extends the user kernel to support demand paging for multiple processes. It initializes and runs user programs. The VMProcess extends the user process and handles page table initialization to allow executable demand paging. It saves and restores process state during context switches and handles exceptions.

1. Virtual Memory

3. public class VMKernel extends UserKernel {

4. “Allocate a new VM kernel.”

5. public VMKernel() {

6. Super(); “this funtion for called proccess”

7. }

8. “Initialize this kernel. ”

9. public void initialize(String[] args) {

10. super.initialize(args);

11. }

13. public void selfTest() {

14. super.selfTest();

15. }

16. “Start running user programs.”

17. public void run() {

18. super.run();

19. }

21. public void terminate() {

22. super.terminate();

23. }

24. // dummy variables to make javac smarter

25. private static VMProcess dummy1 = null;

26. private static final char dbgVM = 'v';

27. }

29. “ Allocate a new process.”

30. public VMProcess() {

31. super();

32. }

33. “Save the state of this process in preparation for a context switch.”

34. “Called by UThread.saveState()”

35. public void saveState() {

36. super.saveState();

37. }

39. public void restoreState() {

40. super.restoreState();

41. }

42. “Initializes page tables for this process so that the executable can be demand-paged.”

43. protected boolean loadSections() {

44. return super.loadSections();

45. }

47. “The cause argument identifies which exception occurred; see the Processor.exception constants.”

48. public void handleException(int cause) {

49. Processor processor = Machine.processor();

50. switch (cause) {

51. default:

52. super.handleException(cause);

53. break;

54. }

55. }

56. private static final int pageSize = Processor.pageSize;

57. private static final char dbgProcess = 'a';

58. private static final char dbgVM = 'v';

59. }