Luna/kernel/src/arch/x86_64/MMU.cpp

#include "arch/MMU.h"
#include "MemoryManager.h"

#define PAGE_SIZE 4096

const u64 rindex = 0776;          // recursive index
const u64 sign = 0177777UL << 48; // sign extension

struct [[gnu::packed]] PageTableEntry
{
    bool present : 1;
    bool read_write : 1;
    bool user : 1;
    bool write_through : 1;
    bool cache_disabled : 1;
    bool accessed : 1;
    bool ignore0 : 1;
    bool larger_pages : 1;
    bool ignore1 : 1;
    u8 available : 3;
    u64 address : 48;
    u8 available2 : 3;
    bool no_execute : 1;

    void set_address(uint64_t addr);
    uint64_t get_address();
};

#pragma GCC push_options
#pragma GCC diagnostic ignored "-Wconversion"

void PageTableEntry::set_address(uint64_t addr)
{
    this->address = (addr >> 12);
}

uint64_t PageTableEntry::get_address()
{
    return (uint64_t)this->address << 12;
}

#pragma GCC pop_options

struct alignas(PAGE_SIZE) PageDirectory
{
    PageTableEntry entries[512];
};

static_assert(sizeof(PageTableEntry) == 8UL);
static_assert(sizeof(PageDirectory) == PAGE_SIZE);

namespace MMU
{
    size_t page_size()
    {
        return PAGE_SIZE;
    }

    PageDirectory* l4_table()
    {
        u64 l4 = sign | (rindex << 39) | (rindex << 30) | (rindex << 21) | (rindex << 12);
        return (PageDirectory*)l4;
    }

    u64 l4_index(u64 addr)
    {
        return (addr >> 39) & 0777;
    }

    PageTableEntry& l4_entry(u64 addr)
    {
        return l4_table()->entries[l4_index(addr)];
    }

    PageDirectory* l3_table(u64 addr)
    {
        u64 l4 = l4_index(addr);
        u64 l3 = sign | (rindex << 39) | (rindex << 30) | (rindex << 21) | (l4 << 12);
        return (PageDirectory*)l3;
    }

    u64 l3_index(u64 addr)
    {
        return (addr >> 30) & 0777;
    }

    PageTableEntry& l3_entry(u64 addr)
    {
        return l3_table(addr)->entries[l3_index(addr)];
    }

    PageDirectory* l2_table(u64 addr)
    {
        u64 l4 = l4_index(addr);
        u64 l3 = l3_index(addr);
        u64 l2 = sign | (rindex << 39) | (rindex << 30) | (l4 << 21) | (l3 << 12);
        return (PageDirectory*)l2;
    }

    u64 l2_index(u64 addr)
    {
        return (addr >> 21) & 0777;
    }

    PageTableEntry& l2_entry(u64 addr)
    {
        return l2_table(addr)->entries[l2_index(addr)];
    }

    PageDirectory* l1_table(u64 addr)
    {
        u64 l4 = l4_index(addr);
        u64 l3 = l3_index(addr);
        u64 l2 = l2_index(addr);
        u64 l1 = sign | (rindex << 39) | (l4 << 30) | (l3 << 21) | (l2 << 12);
        return (PageDirectory*)l1;
    }

    u64 l1_index(u64 addr)
    {
        return (addr >> 12) & 0777;
    }

    PageTableEntry& l1_entry(u64 addr)
    {
        return l1_table(addr)->entries[l1_index(addr)];
    }

    void switch_page_directory(PageDirectory* dir)
    {
        asm volatile("mov %0, %%cr3" : : "r"(dir));
    }

    PageDirectory* get_page_directory()
    {
        PageDirectory* value;
        asm volatile("mov %%cr3, %0" : "=r"(value));
        return value;
    }

    void flush_all()
    {
        switch_page_directory(get_page_directory());
    }

    void flush_page(u64 page)
    {
        asm volatile("invlpg (%0)" : : "r"(page) : "memory");
    }

    Flags arch_flags_to_mmu(PageTableEntry& entry)
    {
        int result = Flags::None;
        if (entry.read_write) result |= Flags::ReadWrite;
        if (entry.user) result |= Flags::User;
        if (entry.no_execute) result |= Flags::NoExecute;
        if (entry.write_through) result |= Flags::WriteThrough;
        if (entry.cache_disabled) result |= Flags::CacheDisable;
        return (Flags)result;
    }

    Result<void> map(u64 virt, u64 phys, Flags flags)
    {
        auto& l4 = l4_entry(virt);
        if (!l4.present)
        {
            auto addr = MemoryManager::alloc_physical_page();
            if (addr.has_error()) return addr.release_error();
            l4.present = true;
            if (flags & Flags::ReadWrite) l4.read_write = true;
            if (flags & Flags::User) l4.user = true;
            l4.set_address(addr.release_value());
        }
        auto& l3 = l3_entry(virt);
        if (!l3.present)
        {
            auto addr = MemoryManager::alloc_physical_page();
            if (addr.has_error()) return addr.release_error();
            l3.present = true;
            if (flags & Flags::ReadWrite) l3.read_write = true;
            if (flags & Flags::User) l3.user = true;
            l3.set_address(addr.release_value());
        }
        if (l3.larger_pages) return err; // FIXME: Replacing larger pages is not supported ATM
        auto& l2 = l2_entry(virt);
        if (!l2.present)
        {
            auto addr = MemoryManager::alloc_physical_page();
            if (addr.has_error()) return addr.release_error();
            l2.present = true;
            if (flags & Flags::ReadWrite) l2.read_write = true;
            if (flags & Flags::User) l2.user = true;
            l2.set_address(addr.release_value());
        }
        if (l2.larger_pages) return err; // FIXME: Replacing larger pages is not supported ATM
        auto& l1 = l1_entry(virt);
        bool was_present = l1.present;
        if (flags & Flags::ReadWrite) l1.read_write = true;
        if (flags & Flags::User) l1.user = true;
        if (flags & Flags::WriteThrough) l1.write_through = true;
        if (flags & Flags::CacheDisable) l1.cache_disabled = true;
        if (flags & Flags::NoExecute) l1.no_execute = true;
        l1.set_address(phys);
        if (was_present) flush_page(virt);
        return {};
    }

    Result<u64> get_physical(u64 virt)
    {
        auto& l4 = l4_entry(virt);
        if (!l4.present) return err;
        auto& l3 = l3_entry(virt);
        if (!l3.present) return err;
        if (l3.larger_pages) return l3.get_address();
        auto& l2 = l2_entry(virt);
        if (!l2.present) return err;
        if (l2.larger_pages) return l2.get_address();
        auto& l1 = l1_entry(virt);
        if (!l1.present) return err;
        return l1.get_address();
    }

    Result<Flags> get_flags(u64 virt)
    {
        auto& l4 = l4_entry(virt);
        if (!l4.present) return err;
        auto& l3 = l3_entry(virt);
        if (!l3.present) return err;
        if (l3.larger_pages) return arch_flags_to_mmu(l3);
        auto& l2 = l2_entry(virt);
        if (!l2.present) return err;
        if (l2.larger_pages) return arch_flags_to_mmu(l2);
        auto& l1 = l1_entry(virt);
        if (!l1.present) return err;
        return arch_flags_to_mmu(l1);
    }

    void setup_initial_page_directory()
    {
        PageDirectory* dir = get_page_directory();
        u64 paddr = (u64)dir;
        PageTableEntry& recursive_entry = dir->entries[rindex];
        recursive_entry.read_write = true;
        recursive_entry.present = true;
        recursive_entry.set_address(paddr);
        flush_all();
    }
}