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

#include "arch/MMU.h"
#include "Log.h"
#include "memory/MemoryManager.h"
#include "memory/MemoryMap.h"
#include <luna/Alignment.h>
#include <luna/CString.h>
#include <luna/Result.h>
#include <luna/ScopeGuard.h>
#include <luna/SystemError.h>

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

PageDirectory* g_kernel_directory;
u64 g_kernel_directory_virt;

// The bootloader maps up to 16GiB of physical memory for us at address 0. Using this bootstrap mapping, we'll map (all)
// physical memory at 0xFFFF800000000000.
u64 g_physical_mapping_base = 0;

void PageTableEntry::set_address(u64 addr)
{
    this->address = (addr >> 12);
}

u64 PageTableEntry::get_address() const
{
    return (u64)this->address << 12;
}

#pragma GCC pop_options

void PageTableEntry::clear()
{
    raw = 0;
}

static bool has_flag(int flags, MMU::Flags flag)
{
    return flags & flag;
}

namespace MMU
{
    template <typename T> T translate_physical(T phys)
    {
        return (T)(g_physical_mapping_base + (u64)phys);
    }

    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;
    }

    PageDirectory* get_virtual_page_directory()
    {
        return translate_physical(get_page_directory());
    }

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

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

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

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

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

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

    int arch_flags_to_mmu(const 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 result;
    }

    PageTableEntry& l4_entry(u64 virt)
    {
        auto index = l4_index(virt);
        return get_virtual_page_directory()->entries[index];
    }

    PageDirectory& page_table(const PageTableEntry& entry)
    {
        return *translate_physical((PageDirectory*)entry.get_address());
    }

    PageTableEntry& l3_entry(const PageTableEntry& entry, u64 virt)
    {
        auto index = l3_index(virt);
        return page_table(entry).entries[index];
    }

    PageTableEntry& l2_entry(const PageTableEntry& entry, u64 virt)
    {
        auto index = l2_index(virt);
        return page_table(entry).entries[index];
    }

    PageTableEntry& l1_entry(const PageTableEntry& entry, u64 virt)
    {
        auto index = l1_index(virt);
        return page_table(entry).entries[index];
    }

    Result<PageTableEntry*> find_entry(u64 virt)
    {
        const auto& l4 = l4_entry(virt);
        if (!l4.present) return err(EFAULT);
        auto& l3 = l3_entry(l4, virt);
        if (!l3.present) return err(EFAULT);
        if (l3.larger_pages) return &l3;
        auto& l2 = l2_entry(l3, virt);
        if (!l2.present) return err(EFAULT);
        if (l2.larger_pages) return &l2;
        return &l1_entry(l2, virt);
    }

    Result<PageTableEntry*> apply_cascading_flags(u64 virt, int flags)
    {
        auto& l4 = l4_entry(virt);
        if (!l4.present) return err(EFAULT);
        if (flags & Flags::ReadWrite) l4.read_write = true;
        if (flags & Flags::User) l4.user = true;
        auto& l3 = l3_entry(l4, virt);
        if (!l3.present) return err(EFAULT);
        if (l3.larger_pages) return &l3;
        if (flags & Flags::ReadWrite) l3.read_write = true;
        if (flags & Flags::User) l3.user = true;
        auto& l2 = l2_entry(l3, virt);
        if (!l2.present) return err(EFAULT);
        if (l2.larger_pages) return &l2;
        if (flags & Flags::ReadWrite) l2.read_write = true;
        if (flags & Flags::User) l2.user = true;
        auto& l1 = l1_entry(l2, virt);
        return &l1;
    }

    Result<void> map(u64 virt, u64 phys, int flags)
    {
        auto& l4 = l4_entry(virt);
        if (!l4.present)
        {
            const u64 addr = TRY(MemoryManager::alloc_frame());
            l4.present = true;
            l4.set_address(addr);
            memset(&page_table(l4), 0, ARCH_PAGE_SIZE);
        }
        if (flags & Flags::ReadWrite) l4.read_write = true;
        if (flags & Flags::User) l4.user = true;

        auto& l3 = l3_entry(l4, virt);
        if (!l3.present)
        {
            const u64 addr = TRY(MemoryManager::alloc_frame());
            l3.present = true;
            l3.set_address(addr);
            memset(&page_table(l3), 0, ARCH_PAGE_SIZE);
        }
        if (flags & Flags::ReadWrite) l3.read_write = true;
        if (flags & Flags::User) l3.user = true;

        if (l3.larger_pages) return err(EFIXME); // FIXME: Replacing larger pages is not supported ATM

        auto& l2 = l2_entry(l3, virt);
        if (!l2.present)
        {
            const u64 addr = TRY(MemoryManager::alloc_frame());
            l2.present = true;
            l2.set_address(addr);
            memset(&page_table(l2), 0, ARCH_PAGE_SIZE);
        }
        if (flags & Flags::ReadWrite) l2.read_write = true;
        if (flags & Flags::User) l2.user = true;

        if (l2.larger_pages) return err(EFIXME); // FIXME: Replacing larger pages is not supported ATM

        auto& l1 = l1_entry(l2, virt);
        if (l1.present) return err(EEXIST); // Please explicitly unmap the page before mapping it again.
        l1.present = true;
        l1.read_write = has_flag(flags, Flags::ReadWrite);
        l1.user = has_flag(flags, Flags::User);
        l1.write_through = has_flag(flags, Flags::WriteThrough);
        l1.cache_disabled = has_flag(flags, Flags::CacheDisable);
        l1.no_execute = has_flag(flags, Flags::NoExecute);
        l1.set_address(phys);
        return {};
    }

    Result<void> remap(u64 virt, int flags)
    {
        auto& l1 = *TRY(apply_cascading_flags(virt, flags));
        if (!l1.present) return err(EFAULT);
        l1.read_write = has_flag(flags, Flags::ReadWrite);
        l1.user = has_flag(flags, Flags::User);
        l1.write_through = has_flag(flags, Flags::WriteThrough);
        l1.cache_disabled = has_flag(flags, Flags::CacheDisable);
        l1.no_execute = has_flag(flags, Flags::NoExecute);
        flush_page(virt);
        return {};
    }

    Result<u64> unmap(u64 virt)
    {
        auto& l1 = *TRY(find_entry(virt));
        if (!l1.present) return err(EFAULT);
        const u64 address = l1.get_address();
        l1.clear();
        flush_page(virt);
        return address;
    }

    Result<u64> get_physical(u64 virt)
    {
        const auto& l1 = *TRY(find_entry(virt));
        if (!l1.present) return err(EFAULT);
        return l1.get_address();
    }

    Result<int> get_flags(u64 virt)
    {
        const auto& l1 = *TRY(find_entry(virt));
        if (!l1.present) return err(EFAULT);
        return arch_flags_to_mmu(l1);
    }

    void setup_initial_page_directory()
    {
        PageDirectory* const dir = get_page_directory();
        g_kernel_directory = dir;

        const u64 physical_memory_base = 0xFFFF800000000000;

        MemoryMapIterator iter;
        const MemoryMapEntry highest_entry = iter.highest();

        const u64 physical_memory_size = highest_entry.address() + highest_entry.size();

        // FIXME: Do this using 2MiB huge pages.
        MemoryManager::map_frames_at(physical_memory_base, 0, physical_memory_size / ARCH_PAGE_SIZE,
                                     MMU::ReadWrite | MMU::NoExecute);

        g_physical_mapping_base = physical_memory_base;

        g_kernel_directory_virt = translate_physical((u64)g_kernel_directory);

        kdbgln("MMU init page directory (ring0): virt %#.16lx, phys %p", g_kernel_directory_virt, g_kernel_directory);
    }

    Result<PageDirectory*> create_page_directory_for_userspace()
    {
        const u64 directory_phys = TRY(MemoryManager::alloc_frame());
        const u64 directory_virt = translate_physical(directory_phys);

        PageDirectory* const directory = (PageDirectory*)directory_virt;
        memset(directory, 0, ARCH_PAGE_SIZE);

        constexpr auto HALF_PAGE = ARCH_PAGE_SIZE / 2;
        // Copy the upper part of the page directory (higher half)
        memcpy(offset_ptr(directory, HALF_PAGE), offset_ptr((PageDirectory*)g_kernel_directory_virt, HALF_PAGE),
               HALF_PAGE);

        kdbgln("MMU init page directory (ring3): virt %p, phys %#.16lx", directory, directory_phys);

        return (PageDirectory*)directory_phys;
    }

    Result<void> delete_userspace_page_directory(PageDirectory* directory)
    {
        check(directory);

        switch_page_directory(g_kernel_directory);

        auto guard = make_scope_guard([directory] { MemoryManager::free_frame((u64)directory); });

        PageDirectory* const table = translate_physical(directory);

        // Let's iterate over every top-level entry, skipping the last two entries (recursive mapping and kernel pages)
        for (u64 i = 0; i < 510; i++)
        {
            PageTableEntry& l4 = table->entries[i];
            if (!l4.present) continue;

            PageDirectory* const pdp = &page_table(l4);

            for (u64 j = 0; j < 512; j++)
            {
                PageTableEntry& l3 = pdp->entries[j];
                if (!l3.present) continue;
                if (l3.larger_pages)
                {
                    // FIXME: Maybe we shouldn't delete some pages in an address space, such as shared memory.
                    TRY(MemoryManager::free_frame(l3.get_address()));
                }

                PageDirectory* const pd = &page_table(l3);

                for (u64 k = 0; k < 512; k++)
                {
                    PageTableEntry& l2 = pd->entries[k];
                    if (!l2.present) continue;
                    if (l2.larger_pages)
                    {
                        // FIXME: Maybe we shouldn't delete some pages in an address space, such as shared memory.
                        TRY(MemoryManager::free_frame(l2.get_address()));
                    }

                    PageDirectory* const pt = &page_table(l2);

                    for (u64 l = 0; l < 512; l++)
                    {
                        PageTableEntry& l1 = pt->entries[l];
                        if (!l1.present) continue;

                        // FIXME: Maybe we shouldn't delete some pages in an address space, such as shared memory.
                        TRY(MemoryManager::free_frame(l1.get_address()));
                    }

                    TRY(MemoryManager::free_frame(l2.get_address()));
                }

                TRY(MemoryManager::free_frame(l3.get_address()));
            }

            TRY(MemoryManager::free_frame(l4.get_address()));
        }

        // No need to clean up manually, the ScopeGuard we set up earlier will do that for us.
        return {};
    }

    PageDirectory* kernel_page_directory()
    {
        return g_kernel_directory;
    }
}