forked from AbleOS/holey-bytes
87 lines
2.1 KiB
Rust
87 lines
2.1 KiB
Rust
//! Page table and associated structures implementation
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use core::{fmt::Debug, mem::MaybeUninit};
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/// Page entry permission
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#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
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#[repr(u8)]
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pub enum Permission {
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/// No page present
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#[default]
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Empty,
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/// Points to another pagetable
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Node,
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/// Page is read only
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Readonly,
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/// Page is readable and writable
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Write,
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/// Page is readable and executable
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Exec,
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}
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/// Page table entry
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#[derive(Clone, Copy, Default, PartialEq, Eq)]
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pub struct PtEntry(u64);
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impl PtEntry {
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/// Create new
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///
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/// # Safety
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/// - `ptr` has to point to valid data and shall not be deallocated
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/// troughout the entry lifetime
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#[inline]
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pub unsafe fn new(ptr: *mut PtPointedData, permission: Permission) -> Self {
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Self(ptr as u64 | permission as u64)
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}
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/// Get permission
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#[inline]
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pub fn permission(&self) -> Permission {
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unsafe { core::mem::transmute(self.0 as u8 & 0b111) }
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}
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/// Get pointer to the data (leaf) or next page table (node)
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#[inline]
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pub fn ptr(&self) -> *mut PtPointedData {
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(self.0 & !((1 << 12) - 1)) as _
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}
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}
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impl Debug for PtEntry {
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fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
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f.debug_struct("PtEntry")
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.field("ptr", &self.ptr())
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.field("permission", &self.permission())
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.finish()
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}
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}
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/// Page table
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#[derive(Clone, Copy, Debug, PartialEq, Eq)]
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#[repr(align(4096))]
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pub struct PageTable {
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/// How much entries are in use
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pub childen: u8,
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/// Entries
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pub table: [PtEntry; 256],
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}
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impl Default for PageTable {
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fn default() -> Self {
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// SAFETY: It's fine, zeroed page table entry is valid (= empty)
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Self {
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childen: 0,
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table: unsafe { MaybeUninit::zeroed().assume_init() },
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}
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}
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}
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/// Data page table entry can possibly point to
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#[derive(Clone, Copy)]
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#[repr(C, align(4096))]
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pub union PtPointedData {
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/// Node - next page table
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pub pt: PageTable,
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/// Leaf
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pub page: u8,
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}
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