Implementing Protection with Virtual Memory - computer architecture:
To enable the operating system to implement protection in the VM system, the HW have to:
I. Support at least 2 modes that denoted whether the running process is a user process (executive process) or an operating system process (kernel/supervisor process).
II. Provide a part ion of the CPU state that a user process may read but not write (includes supervisor mode bit).
o Only operating system process may change page tables. Page tables are held in operating system address space thereby preventing a user procedure from changing them.
o When processes desire to share information in a restricted way, the OS have to assist them.
o The write access bit (in both the TLB and the page table) can be used to limit the sharing to only read sharing.