Question

1. One crucial requirement for demand paging is the ability to restart any instruction after a page fault. A major difficulty arises when one instruction may modify several different memory locations. For instance, consider the IBM System 360/370 MVC (move character) instruction, which can move up to 256 bytes from one location to another (possibly overlapping) location. If either block (source or destination) crosses a page boundary, a page fault might occur after the move is partially done. In addition, if the source and destination blocks overlap, the source block may have been modified, in which case we cannot simply restart the instruction. Can you think of a way to resolve this problem? (3 points)

Answer 1

The below mentioned solution can resolve the given problem:

The microcode performs the computation and based on that it tries to access the both ends of both the blocks. When a page fault is going to happen, then it will occur in this phase before any modification. Then the move can take place. No page fault is possible as all the relevant pages are residing in memory.

Hope this helps.