42-archive/kernel-rs/src/arch/x86/paging/mod.rs

#![allow(dead_code)]

mod table;
mod temporary_page;
mod mapper;

// use memory::*;
use self::mapper::Mapper;
use self::temporary_page::TemporaryPage;
use core::ops::{Deref, DerefMut};
use multiboot2::BootInformation;
use x86::*;
use x86::registers::control::Cr3;
use x86::instructions::tlb;
use x86::structures::paging::*;
use multiboot2;

/// should be called only once
pub fn init(boot_info: &multiboot2::BootInformation) -> ActivePageTable {
    use x86::registers::control::*;
    Cr4::add(Cr4Flags::PSE);
    Cr0::add(Cr0Flags::PAGING | Cr0Flags::WRITE_PROTECT);

    let active_table = remap_the_kernel(boot_info);

    active_table
}

pub struct ActivePageTable {
    mapper: Mapper,
}

impl Deref for ActivePageTable {
    type Target = Mapper;

    fn deref(&self) -> &Mapper {
        &self.mapper
    }
}

impl DerefMut for ActivePageTable {
    fn deref_mut(&mut self) -> &mut Mapper {
        &mut self.mapper
    }
}

impl ActivePageTable {
    pub unsafe fn new() -> ActivePageTable {
        ActivePageTable {
            mapper: Mapper::new(),
        }
    }

    pub fn with<F>(
        &mut self,
        table: &mut InactivePageTable,
        temporary_page: &mut temporary_page::TemporaryPage,
        f: F,
    ) where
        F: FnOnce(&mut Mapper),
    {
        let (cr3_back, _cr3flags_back) = Cr3::read();

        // map temp page to current p2
        let p2_table = temporary_page.map_table_frame(cr3_back.clone(), self);

        // overwrite recursive map
        self.p2_mut()[1023].set(
            table.p2_frame.clone(),
            PageTableFlags::PRESENT | PageTableFlags::WRITABLE,
        );
        tlb::flush_all();

        // execute f in the new context
        f(self);

        // restore recursive mapping to original p2 table
        p2_table[1023].set(cr3_back, PageTableFlags::PRESENT | PageTableFlags::WRITABLE);
    }

    pub fn switch(&mut self, new_table: InactivePageTable) -> InactivePageTable {
        let (p2_frame, cr3_flags) = Cr3::read();
        let old_table = InactivePageTable { p2_frame };

        unsafe {
            Cr3::write(new_table.p2_frame, cr3_flags);
        }

        old_table
    }
}

pub struct InactivePageTable {
    p2_frame: PhysFrame,
}

impl InactivePageTable {
    pub fn new(
        frame: PhysFrame,
        active_table: &mut ActivePageTable,
        temporary_page: &mut TemporaryPage,
    ) -> InactivePageTable {
        {
            let table = temporary_page.map_table_frame(frame.clone(), active_table);

            table.zero();
            // set up recursive mapping for the table
            table[1023].set(
                frame.clone(),
                PageTableFlags::PRESENT | PageTableFlags::WRITABLE,
            )
        }
        temporary_page.unmap(active_table);
        InactivePageTable { p2_frame: frame }
    }
}

pub fn remap_the_kernel(boot_info: &BootInformation) -> ActivePageTable {
    let mut temporary_page = TemporaryPage::new(Page { number: 0xcafe });
    let mut active_table = unsafe { ActivePageTable::new() };
    let mut new_table = {
        let frame = ::memory::allocate_frames(1).expect("no more frames");
        InactivePageTable::new(frame, &mut active_table, &mut temporary_page)
    };

    unsafe {
        asm!("hlt");
    }

    active_table.with(&mut new_table, &mut temporary_page, |mapper| {
        // id map vga buffer
        let vga_buffer_frame = PhysFrame::containing_address(PhysAddr::new(0xb8000));
        mapper.identity_map(vga_buffer_frame, PageTableFlags::WRITABLE);

        let elf_sections_tag = boot_info
            .elf_sections_tag()
            .expect("Memory map tag required");

        // id map kernel sections
        for section in elf_sections_tag.sections() {
            if !section.is_allocated() {
                continue;
            }
            assert!(
                section.start_address() % PAGE_SIZE as u64 == 0,
                "sections need to be page aligned"
            );

            let flags = elf_to_pagetable_flags(&section.flags());
            let start_frame =
                PhysFrame::containing_address(PhysAddr::new(section.start_address() as u32));
            let end_frame =
                PhysFrame::containing_address(PhysAddr::new(section.end_address() as u32 - 1));
            for frame in start_frame..end_frame + 1 {
                mapper.identity_map(frame, flags);
            }
        }

        // id map multiboot
        let multiboot_start =
            PhysFrame::containing_address(PhysAddr::new(boot_info.start_address() as u32));
        let multiboot_end =
            PhysFrame::containing_address(PhysAddr::new(boot_info.end_address() as u32 - 1));
        for frame in multiboot_start..multiboot_end + 1 {
            mapper.identity_map(frame, PageTableFlags::PRESENT);
        }
    });

    let old_table = active_table.switch(new_table);

    let old_p2_page =
        Page::containing_address(VirtAddr::new(old_table.p2_frame.start_address().as_u32()));

    active_table.unmap(old_p2_page);

    active_table
}

fn elf_to_pagetable_flags(elf_flags: &multiboot2::ElfSectionFlags) -> PageTableFlags {
    use multiboot2::ElfSectionFlags;

    let mut flags = PageTableFlags::empty();

    if elf_flags.contains(ElfSectionFlags::ALLOCATED) {
        // section is loaded to memory
        flags = flags | PageTableFlags::PRESENT;
    }
    if elf_flags.contains(ElfSectionFlags::WRITABLE) {
        flags = flags | PageTableFlags::WRITABLE;
    }

    flags
}