page scheme: protection

memory access ranges

For all processes, there is a range of logical addresses. This is usually the same for all processes.

Only some processes may have restricted addresses. This is attached to each page table entry (PTE) as a valid bit. When accessing memory, OS checks against this bit.

Sharing physical memory

Read only pages can be shared across pages. For instance c-stdlib, syscalls.

We can have copy on write, as soon as a process tries to write to a page, we duplicate it before modifying (if it isnt the only one accessing).