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//! Abstractions for reading and modifying the mapping of pages.

pub use self::recursive::RecursivePageTable;
pub use self::offset::OffsetMapper;

use crate::instructions::tlb;
use crate::registers::control::Cr3;
use crate::structures::paging::{
    frame_alloc::FrameAllocator,
    page_table::{FrameError, PageTable, PageTableEntry, PageTableFlags},
    page::NotGiantPageSize, Page, PageSize, PhysFrame, Size1GiB, Size2MiB, Size4KiB,
};
use crate::{PhysAddr, VirtAddr};
use ux::u9;

mod offset;
mod recursive;

/// A trait for common page table operations.
pub trait Mapper<S: PageSize> {
    /// Creates a new mapping in the page table.
    ///
    /// This function might need additional physical frames to create new page tables. These
    /// frames are allocated from the `allocator` argument. At most three frames are required.
    ///
    /// This function is unsafe because the caller must guarantee the following:
    ///
    /// - The passed `frame` must be unused, i.e. not used for any other mappings.
    /// - The passed `frame_allocator` must only yield unused frames.
    unsafe fn map_to<A>(
        &mut self,
        page: Page<S>,
        frame: PhysFrame<S>,
        flags: PageTableFlags,
        frame_allocator: &mut A,
    ) -> Result<MapperFlush<S>, MapToError>
    where
        A: FrameAllocator<Size4KiB>;

    /// Removes a mapping from the page table and returns the frame that used to be mapped.
    ///
    /// Note that no page tables or pages are deallocated.
    fn unmap(&mut self, page: Page<S>) -> Result<(PhysFrame<S>, MapperFlush<S>), UnmapError>;

    /// Updates the flags of an existing mapping.
    fn update_flags(
        &mut self,
        page: Page<S>,
        flags: PageTableFlags,
    ) -> Result<MapperFlush<S>, FlagUpdateError>;

    /// Return the frame that the specified page is mapped to.
    fn translate_page(&self, page: Page<S>) -> Result<PhysFrame<S>, TranslateError>;

    /// Maps the given frame to the virtual page with the same address.
    ///
    /// This function is unsafe because the caller must guarantee the following:
    ///
    /// - The passed `frame` must be unused, i.e. not used for any other mappings.
    /// - The passed `frame_allocator` must only yield unused frames.
    unsafe fn identity_map<A>(
        &mut self,
        frame: PhysFrame<S>,
        flags: PageTableFlags,
        frame_allocator: &mut A,
    ) -> Result<MapperFlush<S>, MapToError>
    where
        A: FrameAllocator<Size4KiB>,
        S: PageSize,
        Self: Mapper<S>,
    {
        let page = Page::containing_address(VirtAddr::new(frame.start_address().as_u64()));
        self.map_to(page, frame, flags, frame_allocator)
    }
}

/// This type represents a page whose mapping has changed in the page table.
///
/// The old mapping might be still cached in the translation lookaside buffer (TLB), so it needs
/// to be flushed from the TLB before it's accessed. This type is returned from function that
/// change the mapping of a page to ensure that the TLB flush is not forgotten.
#[derive(Debug)]
#[must_use = "Page Table changes must be flushed or ignored."]
pub struct MapperFlush<S: PageSize>(Page<S>);

impl<S: PageSize> MapperFlush<S> {
    /// Create a new flush promise
    fn new(page: Page<S>) -> Self {
        MapperFlush(page)
    }

    /// Flush the page from the TLB to ensure that the newest mapping is used.
    pub fn flush(self) {
        tlb::flush(self.0.start_address());
    }

    /// Don't flush the TLB and silence the “must be used” warning.
    pub fn ignore(self) {}
}

/// This error is returned from `map_to` and similar methods.
#[derive(Debug)]
pub enum MapToError {
    /// An additional frame was needed for the mapping process, but the frame allocator
    /// returned `None`.
    FrameAllocationFailed,
    /// An upper level page table entry has the `HUGE_PAGE` flag set, which means that the
    /// given page is part of an already mapped huge page.
    ParentEntryHugePage,
    /// The given page is already mapped to a physical frame.
    PageAlreadyMapped,
}

/// An error indicating that an `unmap` call failed.
#[derive(Debug)]
pub enum UnmapError {
    /// An upper level page table entry has the `HUGE_PAGE` flag set, which means that the
    /// given page is part of a huge page and can't be freed individually.
    ParentEntryHugePage,
    /// The given page is not mapped to a physical frame.
    PageNotMapped,
    /// The page table entry for the given page points to an invalid physical address.
    InvalidFrameAddress(PhysAddr),
}

/// An error indicating that an `update_flags` call failed.
#[derive(Debug)]
pub enum FlagUpdateError {
    /// The given page is not mapped to a physical frame.
    PageNotMapped,
    /// An upper level page table entry has the `HUGE_PAGE` flag set, which means that the
    /// given page is part of a huge page and can't be freed individually.
    ParentEntryHugePage,
}

/// An error indicating that an `translate` call failed.
#[derive(Debug)]
pub enum TranslateError {
    /// The given page is not mapped to a physical frame.
    PageNotMapped,
    /// An upper level page table entry has the `HUGE_PAGE` flag set, which means that the
    /// given page is part of a huge page and can't be freed individually.
    ParentEntryHugePage,
    /// The page table entry for the given page points to an invalid physical address.
    InvalidFrameAddress(PhysAddr),
}