Demystifying address translation and MMU
MMU does not only convert virtual addresses into physical ones but also protects memory from unauthorized access. Given a process, any page that needs to be accessed from this process must exist in one of its VMAs and, thus, must live in the process's page table (every process has its own).
As a recall, memory is organized by chunks of fixed-size named pages for virtual memory and frames for physical memory. The size in our case is 4 KB. However, it is defined and accessible with the PAGE_SIZE macro in the kernel. Remember, however, that page size is imposed by the hardware. Considering a 4 KB page-sized system, bytes 0 to 4095 fall on page 0, bytes 4096 to 8191 fall on page 1, and so on.
The concept of a page table is introduced to manage mapping between pages and frames. Pages are spread over tables so that each PTE corresponds to a mapping between a page and a frame. Each process is then given a set of page tables to describe all...
