Mapper (Virtual Memory Management)

Mapper is a trait that provides a way to map and unmap virtual memory. It is defined in awkernel_lib/src/paging.rs as follows.

#![allow(unused)]
fn main() {
pub trait Mapper {
    /// Return the physical address of `vm_addr`.
    fn vm_to_phy(vm_addr: VirtAddr) -> Option<PhyAddr>;

    /// Map `vm_addr` to `phy_addr` with `flag`.
    ///
    /// # Safety
    ///
    /// - Virtual memory must be enabled.
    /// - `flag` must be reasonable.
    /// - `phy_addr` must be being unmapped.
    unsafe fn map(vm_addr: VirtAddr, phy_addr: PhyAddr, flags: Flags) -> Result<(), MapError>;

    /// Unmap `vm_addr`.
    ///
    /// # Safety
    ///
    /// - Virtual memory must be enabled.
    /// - `vm_addr` must be being mapped.
    unsafe fn unmap(vm_addr: VirtAddr);
}
}

Mapper uses VirtAddr and PhyAddr types to represent virtual and physical addresses. These types are defined in awkernel_lib/src/addr/virt_addr.rs and awkernel_lib/src/addr/phy_addr.rs.

The Flags type is used to represent the flags of the page table entry. It is defined in awkernel_lib/src/paging.rs as follows.

#![allow(unused)]
fn main() {
/// Flag for a page.
/// Note that every page is readable.
#[derive(Debug, Clone, Copy)]
pub struct Flags {
    pub execute: bool,       // executable
    pub write: bool,         // writable
    pub cache: bool,         // enable cache
    pub write_through: bool, // write back if disabled
    pub device: bool,        // this page is for MMIO, ignored on x86
}
}

There are functions regarding the Mapper trait in awkernel_lib/src/paging.rs as follows.

Awkernel's page size is 4 KiB and it is defined by PAGESIZE:awkernel_lib/src/paging.rs.

#![allow(unused)]
fn main() {
pub const PAGESIZE: usize = 4 * 1024;
}

Implementation

x86_64

For x86_64, the X86 structure implements the Mapper trait in awkernel_lib/src/arch/x86_64/paging.rs. To handle page tables, the OffsetPageTable structure defined in the x86_64 crate is used.

AArch64

For AArch64, the AArch64 structure implements the Mapper trait in awkernel_lib/src/arch/aarch64/paging.rs. To handle page tables, the PageTable structure defined in the awkernel_lib/src/arch/aarch64/page_table.rs is used.