Struct aarch64_paging::idmap::IdMap

pub struct IdMap { /* private fields */ }

Manages a level 1 page table using identity mapping, where every virtual address is either unmapped or mapped to the identical IPA.

This assumes that identity mapping is used both for the page table being managed, and for code that is managing it.

Mappings should be added with map_range before calling activate to start using the new page table. To make changes which may require break-before-make semantics you must first call deactivate to switch back to a previous static page table, and then activate again after making the desired changes.

Example

use aarch64_paging::{
    idmap::IdMap,
    paging::{Attributes, MemoryRegion},
};

const ASID: usize = 1;
const ROOT_LEVEL: usize = 1;

// Create a new page table with identity mapping.
let mut idmap = IdMap::new(ASID, ROOT_LEVEL);
// Map a 2 MiB region of memory as read-write.
idmap.map_range(
    &MemoryRegion::new(0x80200000, 0x80400000),
    Attributes::NORMAL | Attributes::NON_GLOBAL | Attributes::EXECUTE_NEVER,
).unwrap();
// Set `TTBR0_EL1` to activate the page table.
idmap.activate();

// Write something to the memory...

// Restore `TTBR0_EL1` to its earlier value while we modify the page table.
idmap.deactivate();
// Now change the mapping to read-only and executable.
idmap.map_range(
    &MemoryRegion::new(0x80200000, 0x80400000),
    Attributes::NORMAL | Attributes::NON_GLOBAL | Attributes::READ_ONLY,
).unwrap();
idmap.activate();

Implementations

impl IdMap

pub fn new(asid: usize, rootlevel: usize) -> Self

Creates a new identity-mapping page table with the given ASID and root level.

pub fn activate(&mut self)

Activates the page table by setting TTBR0_EL1 to point to it, and saves the previous value of TTBR0_EL1 so that it may later be restored by deactivate.

Panics if a previous value of TTBR0_EL1 is already saved and not yet used by a call to deactivate.

pub fn deactivate(&mut self)

Deactivates the page table, by setting TTBR0_EL1 back to the value it had before activate was called, and invalidating the TLB for this page table’s configured ASID.

Panics if there is no saved TTRB0_EL1 value because activate has not previously been called.

pub fn map_range(
    &mut self,
    range: &MemoryRegion,
    flags: Attributes
) -> Result<(), MapError>

Maps the given range of virtual addresses to the identical physical addresses with the given flags.

This should generally only be called while the page table is not active. In particular, any change that may require break-before-make per the architecture must be made while the page table is inactive. Mapping a previously unmapped memory range may be done while the page table is active.

Errors

Returns MapError::AddressRange if the largest address in the range is greater than the largest virtual address covered by the page table given its root level.

Trait Implementations

impl Debug for IdMap

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.