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Diffstat (limited to 'arch/x86_64/arch/memory/page_table.hpp')
| -rw-r--r-- | arch/x86_64/arch/memory/page_table.hpp | 232 |
1 files changed, 232 insertions, 0 deletions
diff --git a/arch/x86_64/arch/memory/page_table.hpp b/arch/x86_64/arch/memory/page_table.hpp new file mode 100644 index 0000000..ce3d3a1 --- /dev/null +++ b/arch/x86_64/arch/memory/page_table.hpp @@ -0,0 +1,232 @@ +#ifndef TEACHOS_X86_64_PAGE_TABLE_HPP +#define TEACHOS_X86_64_PAGE_TABLE_HPP + +#include <kapi/memory.hpp> + +#include <kstd/ext/bitfield_enum> +#include <kstd/units> + +#include <array> +#include <cstddef> +#include <cstdint> +#include <optional> +#include <type_traits> + +namespace arch::memory +{ + + //! A table containing page mapping entries. + //! + //! Page tables exist in a multi-level hierarchy and are used to map pages (virtual memory) onto frames (physical + //! memory). Conceptually, pages represent the data found in a virtual address space, while frames represent their + //! storage. In most cases, only a level 1 page table maps an actual page onto a frame. All other page tables on + //! higher levels do not map payload pages, but rather their subordinate page tables. The only exception to that rule + //! is the use of huge pages. + struct page_table + { + //! An entry in a page table. + //! + //! A page table entry is a combination of a frame number and a set of flags that determine the properties and + //! access rights to a mapped page. Entries at a higher level in the page hierarchy do not map a page directly, + //! unless that page is marked as huge on the relevant level, but rather map the next lower page table. + struct entry + { + //! Flags marking the state and configuration of an entry. + //! + //! An entry in a page table may have any combination of these flags active at the same time. The final flags of a + //! page are determined as the strictest combination (logical AND) of all flags along the hierarchy. + //! + //! @note This is a bitfield enum as defined by kstd::ext::bitfield_enum. + enum struct flags : std::uint64_t + { + empty = 0, + present = 1uz << 0, //!< The page is mapped. + writable = 1uz << 1, //!< The page is writable. + user_accessible = 1uz << 2, //!< The page is accessible in user mode. + write_through = 1uz << 3, //!< Any writes to the page must immediately hit memory. + disable_cache = 1uz << 4, //!< Any writes to the page must never be cached. + accessed = 1uz << 5, //!< The page was accessed. + dirty = 1uz << 6, //!< The page was written to. + huge_page = 1uz << 7, //!< The page is huge. + global = 1uz << 8, //!< The TLB entry for this page must not be flushed on context switches. + no_execute = 1uz << 63, //!< The data in this page must not be executed. + }; + + //! Construct an empty entry. + entry() = default; + + //! Clear this entry, ensuring all information is set to zero. + //! + //! This effectively marks the page represented by this entry as not present. In addition, it also removes any + //! information about the frame referenced by this entry. + auto clear() noexcept -> void; + + //! Check if the page represented by this entry is present. + //! + //! @note This function does not attempt to walk the page table hierarchy, but only performs a local check. This + //! means, that if the page is not mapped at a lower level, this will not be detected. + //! + //! @return @p true iff. the page is present at this level, @p false otherwise. + [[nodiscard]] auto present() const noexcept -> bool; + + //! Check if the page represented by this entry is a huge page. + //! + //! @note The effective size of the page depends on the level of the page table containing this entry. + //! + //! @return @p true iff. the page is marked as being huge, @p false otherwise. + [[nodiscard]] auto huge() const noexcept -> bool; + + //! Get all flags present in this entry. + //! + //! @return The flags that are currently set on this entry. + [[nodiscard]] auto all_flags() const noexcept -> flags; + + //! Set all flags of this entry. + //! + //! @param flags The flags to apply to this entry. + auto all_flags(flags flags) noexcept -> void; + + //! Add the given flags to the flags of this entry. + //! + //! @param rhs The flags to add to this entry's flags. + //! @return A reference to this entry. + auto operator|=(flags rhs) noexcept -> entry &; + + //! Get the frame number associated with this entry, if the referenced page is present. + //! + //! @return an engaged std::optional iff. this entry maps a page, std::nullopt otherwise. + [[nodiscard]] auto frame() const noexcept -> std::optional<kapi::memory::frame>; + + //! Map this entry. + //! + //! @param frame The frame to map in this entry. + //! @param flags The flags to apply to this entry. + auto frame(kapi::memory::frame frame, flags flags) noexcept -> void; + + private: + //! A mask to retrieve, or exclude, the frame number from the raw entry. + //! + //! Page table entries in x86_64 are a compacted combination of the relevant flags and the frame number. This mask + //! represents the bits that make up the frame number in an entry. + constexpr auto static frame_number_mask{0x000f'ffff'ffff'f000uz}; + + //! The raw entry bytes. + //! + //! @see entry::frame_number_mask + std::uint64_t m_raw{}; + }; + + //! The maximum number of entries in this table. + constexpr auto static entry_count{kapi::memory::page::size / kstd::units::bytes{sizeof(entry)}}; + + //! Get the entry at the given index. + //! + //! @warning This function will panic if the entry index is out of bounds. + //! + //! @param index The index of the desired entry. + //! @return A reference to the entry at the given index. + [[nodiscard]] auto operator[](std::size_t index) -> entry &; + + //! @copydoc page_table::operator[] + [[nodiscard]] auto operator[](std::size_t index) const -> entry const &; + + //! Clear the entire page table. + //! + //! This function effectively marks the page table as not mapping any pages. + auto clear() noexcept -> void; + + //! Check if the page table is empty. + //! + //! @return @p true iff. this page table has no entries marked present, @p false otherwise. + [[nodiscard]] auto empty() const noexcept -> bool; + + private: + std::array<entry, entry_count> m_entries{}; + }; + +} // namespace arch::memory + +namespace kstd::ext +{ + template<> + struct is_bitfield_enum<arch::memory::page_table::entry::flags> : std::true_type + { + }; +} // namespace kstd::ext + +namespace arch::memory +{ + + constexpr auto to_mapper_flags(page_table::entry::flags flags) -> kapi::memory::page_mapper::flags + { + using table_flags = page_table::entry::flags; + using mapper_flags = kapi::memory::page_mapper::flags; + + auto result = mapper_flags{}; + + if ((flags & table_flags::no_execute) == table_flags::empty) + { + result |= mapper_flags::executable; + } + + if ((flags & table_flags::writable) != table_flags::empty) + { + result |= mapper_flags::writable; + } + + if ((flags & (table_flags::disable_cache | table_flags::write_through)) != table_flags::empty) + { + result |= mapper_flags::uncached; + } + + if ((flags & table_flags::user_accessible) == table_flags::empty) + { + result |= mapper_flags::supervisor_only; + } + + if ((flags & table_flags::global) != table_flags::empty) + { + result |= mapper_flags::global; + } + + return result; + } + + constexpr auto to_table_flags(kapi::memory::page_mapper::flags flags) -> page_table::entry::flags + { + using table_flags = page_table::entry::flags; + using mapper_flags = kapi::memory::page_mapper::flags; + + auto result = table_flags{}; + + if ((flags & mapper_flags::executable) == mapper_flags::empty) + { + result |= table_flags::no_execute; + } + + if ((flags & mapper_flags::writable) != mapper_flags::empty) + { + result |= table_flags::writable; + } + + if ((flags & mapper_flags::uncached) != mapper_flags::empty) + { + result |= (table_flags::disable_cache | table_flags::write_through); + } + + if ((flags & mapper_flags::supervisor_only) == mapper_flags::empty) + { + result |= table_flags::user_accessible; + } + + if ((flags & mapper_flags::global) != mapper_flags::empty) + { + result |= table_flags::global; + } + + return result; + } + +} // namespace arch::memory + +#endif |