Introduction

This crate implements a generic page table walker in Rust, which can be used to either introspect or manage virtual address spaces on architectures that implement a Memory Management Unit (MMU) that traverses a hierarchy of page tables to translate virtual address into physical addresses and a set of permissions. Note that paging is not limited to CPUs, and that paging is also common on modern GPUs. The implementations provided here may therefore be useful when implementing drivers for any sort of paging architecture, an operating system, a hypervisor, etc.

lib.rs:

This crate implements a generic page table walker in Rust, which can be used to either introspect or manage virtual address spaces on architectures that implement a Memory Management Unit (MMU) that traverses a hierarchy of page tables to translate virtual address into physical addresses and a set of permissions. Note that paging is not limited to CPUs, and that paging is also common on modern GPUs. The implementations provided here may therefore be useful when implementing drivers for any sort of paging architecture, an operating system, a hypervisor, etc.

The page table hierarchies of different architectures are described in the arch module. In particular, the PageFormat struct is used to describe a page table hierarchy or layout consisting of one or more PageLevel structs, where each level describes which virtual address bits are used to index into the page table. PageFormat::walk and PageFormat::walk_mut implement a software page table walker that essentially starts at the root address and traverses the page tables one by one using the PageFormat struct to select the appropriate bits from the virtual address to index into these page tables.

While traversing the page tables, the PageFormat::walk and PageFormat::walk_mut invoke functions provided by a user supplied type implementing the PageWalker and PageWalkerMut traits respectively to operate on the various page table entries (PTEs). Note that there is an immutable version that does not allow modification of the page tables, and a mutable version that does.

While it is possible to implement your own PageWalker and PageWalkerMut, this crate also provides a higher-level abstraction of an virtual address space in AddressSpace that only requires you to implement a PageTableMapper for mapping and unmapping page tables. The AddressSpace then simply offers you the functionality to retrieve and modify the PTEs of existing pages.

In addition, when PageTableMapper::alloc_page and PageTableMapper::free_page are implemented, the full range of functionality can be used. More specifically, the AddressSpace provides functions to allocate and free pages for a given virtual address range, change the protection of a given virtual address range and allows mapping and unmapping a physical address range to a given virtual address range for memory-mapped I/O.