Chapter 3 Page tables

Page tables are the most popular mechanism through which the operating system provides each process with its own private address space and memory. Page tables determine what memory addresses mean, and what parts of physical memory can be accessed. They allow xv6 to isolate different processes’ address spaces and to multiplex them onto a single physical memory. Page tables provide a level of indirection that allows operating systems to perform many useful tricks. Xv6 performs a few: mapping the same memory (a trampoline page) in several address spaces, guarding kernel and user stacks with an unmapped page, and allocating user heap memory lazily. The rest of this chapter explains the page tables that the RISC-V hardware provides and how xv6 uses them.