33.3 Exercises

1:

The second example in Section 33.2.1 states that "user level processes can alter page table entries, so references to those data structures also fail to meet the second requirement." How can an operating system prevent a user level process from altering its page table entries?

2:

Suppose a virtual machine monitor (call it VMM-1) is running another virtual machine monitor (VMM-2), which in turn is running a version of the Linux operating system. The user running the Linux system is editing a file. The user requests that the editor write the file to disk. Is the instruction RFT (Return From Trap) sensitive? Why or why not? Trace the flow of control among VMM-1, VMM-2, Linux, and the editor. How many RFT instructions will be executed? Justify your answer.