1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135

use super::*;

const PAGE_SIZE: u64 = 0x1000;
const PT_SIZE:   u64 = 512;

const PT1_EXTENT: u64 = PAGE_SIZE * PT_SIZE;
const PT2_EXTENT: u64 = PT_SIZE * PT1_EXTENT;
const PT3_EXTENT: u64 = PT_SIZE * PT2_EXTENT;

/// Provides access to page table entries.
pub struct RecursiveMapper<AllocFrame, TranslateAddress>
where AllocFrame: FnMut() -> Result<PhysicalAddress>, TranslateAddress: FnMut(PhysicalAddress) -> VirtualAddress {
    pt4: *mut PageTable,
    alloc_frame: AllocFrame,
    translate_address: TranslateAddress,
}

impl<AllocFrame, TranslateAddress> RecursiveMapper<AllocFrame, TranslateAddress>
where AllocFrame: FnMut() -> Result<PhysicalAddress>, TranslateAddress: FnMut(PhysicalAddress) -> VirtualAddress {
    /// Create a new `RecursiveMapper` object.
    pub unsafe fn new(
        pt4: *mut PageTable,
        alloc_frame: AllocFrame,
        translate_address: TranslateAddress
    ) -> Self {
        RecursiveMapper {
            pt4: pt4,
            alloc_frame: alloc_frame,
            translate_address: translate_address,
        }
    }

    unsafe fn ensure_subtable(&mut self, entry: &mut Entry) -> Result<()> {
        if !entry.bit(Bit::Present) {
            let frame = (self.alloc_frame)()?;
            let addr = (self.translate_address)(frame);
            let table = &mut *(addr as *mut PageTable);
            table.clear();
            entry.set_address(frame);

            // Mark table present.
            entry.set_bit(Bit::Present);

            // Set writable and user bit. If we didn't set these bits
            // the user wouldn't be able to.
            entry.set_bit(Bit::Writable);
            entry.set_bit(Bit::User);
            Ok(())
        }
        else {
            if entry.bit(Bit::Huge) {
                Err(Error::Overlap)
            }
            else {
                Ok(())
            }
        }
    }

    unsafe fn descend_entry(&mut self, entry: &mut Entry) -> Result<&'static mut PageTable> {
        self.ensure_subtable(entry)?;
        let phys_addr = entry.address();
        let virt_addr = (self.translate_address)(phys_addr);
        Ok(&mut *(virt_addr as *mut PageTable))
    }

    /// Get the page table entry for a virtual address.
    pub unsafe fn entry(&mut self, virt_addr: VirtualAddress, level: u8) -> Result<&'static mut Entry> {
        assert!(!(level < 1 && level > 4));
        assert!(level != 1 || virt_addr % PAGE_SIZE == 0);
        assert!(level != 2 || virt_addr % PT1_EXTENT == 0);
        assert!(level != 3 || virt_addr % PT2_EXTENT == 0);
        assert!(level != 4 || virt_addr % PT3_EXTENT == 0);

        let virt_addr = virt_addr & !0xffff_0000_0000_0000;

        let pt4 = &mut *self.pt4;
        let pt4_idx = virt_addr / PT3_EXTENT;
        let pt4_entry = &mut pt4[pt4_idx as usize];
        if level == 4 { return Ok(pt4_entry); }

        let pt3 = self.descend_entry(pt4_entry)?;
        let pt3_idx = (virt_addr % PT3_EXTENT) / PT2_EXTENT;
        let pt3_entry = &mut pt3[pt3_idx as usize];
        if level == 3 { return Ok(pt3_entry); }

        let pt2 = self.descend_entry(pt3_entry)?;
        let pt2_idx = (virt_addr % PT2_EXTENT) / PT1_EXTENT;
        let pt2_entry = &mut pt2[pt2_idx as usize];
        if level == 2 { return Ok(pt2_entry); }

        let pt1 = self.descend_entry(pt2_entry)?;
        let pt1_idx = (virt_addr % PT1_EXTENT) / PAGE_SIZE;
        Ok(&mut pt1[pt1_idx as usize]) }
}

#[test]
fn map_tables() {
    unsafe {
        let layout = std::alloc::Layout::from_size_align(0x100_0000, 0x1000).unwrap();
        let memory_addr = std::alloc::alloc(layout.clone()) as PhysicalAddress;

        let pt4_addr = (memory_addr) as *mut PageTable;

        let mut current_addr = 0x1000;

        let mut mapper = RecursiveMapper::new(pt4_addr,
            || {
                let result = current_addr;
                current_addr += 0x1000;
                println!("ALLOC: {:#x}", result);
                Ok(result)
            },
            |phys_addr| {
                memory_addr + phys_addr
            }
        );

        let entry = mapper.entry(0xffff_8000_0000_0000, 1).unwrap();

        let pt4 = &mut *pt4_addr;
        let pt3_addr = (memory_addr + pt4[256].address()) as *mut PageTable;
        let pt3 = &mut *pt3_addr;
        let pt2_addr = (memory_addr + pt3[0].address()) as *mut PageTable;
        let pt2 = &mut *pt2_addr;
        let pt1_addr = (memory_addr + pt2[0].address()) as *mut PageTable;

        assert_eq!(pt4_addr.offset(1), pt3_addr);
        assert_eq!(pt3_addr.offset(1), pt2_addr);
        assert_eq!(pt2_addr.offset(1), pt1_addr);
        assert_eq!(pt1_addr, entry as *mut _ as _);

        std::alloc::dealloc(memory_addr as _, layout);
    }
}