Luna/kernel/src/memory/MemoryManager.cpp

#include "memory/MemoryManager.h"
#include "Log.h"
#include "arch/MMU.h"
#include "boot/bootboot.h"
#include <Alignment.h>
#include <String.h>
#include <SystemError.h>
#include <Types.h>

extern BOOTBOOT bootboot;

extern u8 start_of_kernel_rodata[1];
extern u8 end_of_kernel_rodata[1];
extern u8 start_of_kernel_data[1];
extern u8 end_of_kernel_data[1];

static bool page_bitmap_read(u64 index);
static void page_bitmap_set(u64 index, bool value);

static u64 free_mem = 0;
static u64 used_mem = 0;
static u64 reserved_mem = 0;

static char* page_bitmap_addr = nullptr;
static char* page_virtual_bitmap_addr = nullptr;
static u64 page_bitmap_size;

static u64 start_index = 0;

static bool page_bitmap_read(u64 index)
{
    return (page_virtual_bitmap_addr[index / 8] & (0b10000000 >> (index % 8))) > 0;
}

static void page_bitmap_set(u64 index, bool value)
{
    u64 byte_index = index / 8;
    u8 mask = 0b10000000 >> (index % 8);
    page_virtual_bitmap_addr[byte_index] &= (u8)(~mask);
    if (value) { page_virtual_bitmap_addr[byte_index] |= mask; }
}

#define CHECK_PAGE_ALIGNED(address) check(is_aligned(address, ARCH_PAGE_SIZE))

namespace MemoryManager
{
    Result<void> protect_kernel_sections()
    {
        const u64 rodata_size = (u64)(end_of_kernel_rodata - start_of_kernel_rodata);
        const u64 rodata_pages = get_blocks_from_size(rodata_size, ARCH_PAGE_SIZE);
        TRY(remap((u64)start_of_kernel_rodata, rodata_pages, MMU::NoExecute));

        const u64 data_size = (u64)(end_of_kernel_data - start_of_kernel_data);
        const u64 data_pages = get_blocks_from_size(data_size, ARCH_PAGE_SIZE);
        TRY(remap((u64)start_of_kernel_data, data_pages, MMU::NoExecute | MMU::ReadWrite));

        return {};
    }

    void init_physical_allocator()
    {
        u64 total_mem = 0;

        void* biggest_memory_block = nullptr;
        u64 biggest_memory_block_size = 0;

        // walk the memory map
        MMapEnt* ptr = &bootboot.mmap;
        u64 mmap_entries = (bootboot.size - 128) / 16;
        for (u64 i = 0; i < mmap_entries; i++)
        {
            u64 size = MMapEnt_Size(ptr);
            total_mem += size;
            if (!MMapEnt_IsFree(ptr))
            {
                ptr++;
                continue;
            }
            if (size > biggest_memory_block_size)
            {
                biggest_memory_block = (void*)MMapEnt_Ptr(ptr);
                biggest_memory_block_size = MMapEnt_Size(ptr);
            }
            ptr++;
        }

        page_bitmap_addr = (char*)biggest_memory_block;
        page_virtual_bitmap_addr = page_bitmap_addr; // we'll map this to virtual memory as soon as the MMU is ready
        if ((total_mem / ARCH_PAGE_SIZE / 8) >= biggest_memory_block_size)
        {
            kerrorln("ERROR: No single memory block is enough to hold the page bitmap");
            for (;;)
                ;
        }

        page_bitmap_size = total_mem / ARCH_PAGE_SIZE / 8 + 1;
        memset(page_bitmap_addr, 0xFF, page_bitmap_size);

        ptr = &bootboot.mmap;
        for (u64 i = 0; i < mmap_entries; i++)
        {
            u64 index = MMapEnt_Ptr(ptr) / ARCH_PAGE_SIZE;
            if (!MMapEnt_IsFree(ptr)) { reserved_mem += MMapEnt_Size(ptr); }
            else
            {
                free_mem += MMapEnt_Size(ptr);
                for (u64 j = 0; j < (MMapEnt_Size(ptr) / ARCH_PAGE_SIZE); j++) { page_bitmap_set(index + j, false); }
            }
            ptr++;
        }

        lock_frames((u64)page_bitmap_addr, page_bitmap_size / ARCH_PAGE_SIZE + 1);
    }

    void init()
    {
        init_physical_allocator();
        MMU::setup_initial_page_directory();
    }

    void lock_frame(u64 frame)
    {
        const u64 index = ((u64)frame) / ARCH_PAGE_SIZE;
        if (page_bitmap_read(index)) return;
        page_bitmap_set(index, true);
        used_mem += ARCH_PAGE_SIZE;
        free_mem -= ARCH_PAGE_SIZE;
    }

    void lock_frames(u64 frames, u64 count)
    {
        for (u64 index = 0; index < count; index++) { lock_frame(frames + (index * ARCH_PAGE_SIZE)); }
    }

    Result<u64> alloc_frame()
    {
        for (u64 index = start_index; index < (page_bitmap_size * 8); index++)
        {
            if (page_bitmap_read(index)) continue;
            page_bitmap_set(index, true);
            start_index = index + 1;
            free_mem -= ARCH_PAGE_SIZE;
            used_mem += ARCH_PAGE_SIZE;
            return index * ARCH_PAGE_SIZE;
        }

        return err(ENOMEM);
    }

    Result<void> free_frame(u64 frame)
    {
        const u64 index = frame / ARCH_PAGE_SIZE;
        if (index > (page_bitmap_size * 8)) return err(EFAULT);
        if (!page_bitmap_read(index)) return err(EFAULT);
        page_bitmap_set(index, false);
        used_mem -= ARCH_PAGE_SIZE;
        free_mem += ARCH_PAGE_SIZE;
        if (start_index > index) start_index = index;
        return {};
    }

    Result<void> remap(u64 address, usize count, int flags)
    {
        CHECK_PAGE_ALIGNED(address);

        while (count--)
        {
            TRY(MMU::remap(address, flags));
            address += ARCH_PAGE_SIZE;
        }

        return {};
    }

    Result<void> map_frames_at(u64 virt, u64 phys, usize count, int flags)
    {
        CHECK_PAGE_ALIGNED(virt);
        CHECK_PAGE_ALIGNED(phys);

        while (count--)
        {
            TRY(MMU::map(virt, phys, flags));
            virt += ARCH_PAGE_SIZE;
            phys += ARCH_PAGE_SIZE;
        }

        return {};
    }

    Result<u64> alloc_at(u64 virt, usize count, int flags)
    {
        CHECK_PAGE_ALIGNED(virt);

        u64 start = virt;

        while (count--)
        {
            u64 frame = TRY(alloc_frame());
            TRY(MMU::map(virt, frame, flags));
            virt += ARCH_PAGE_SIZE;
        }

        return start;
    }

    Result<void> unmap_owned(u64 virt, usize count)
    {
        CHECK_PAGE_ALIGNED(virt);

        while (count--)
        {
            u64 frame = TRY(MMU::unmap(virt));
            TRY(free_frame(frame));
            virt += ARCH_PAGE_SIZE;
        }

        return {};
    }

    Result<void> unmap_weak(u64 virt, usize count)
    {
        CHECK_PAGE_ALIGNED(virt);

        while (count--)
        {
            TRY(MMU::unmap(virt));
            virt += ARCH_PAGE_SIZE;
        }

        return {};
    }

    Result<void> remap_unaligned(u64 address, usize count, int flags)
    {
        if (!is_aligned(address, ARCH_PAGE_SIZE)) count++;
        address = align_down(address, ARCH_PAGE_SIZE);

        while (count--)
        {
            TRY(MMU::remap(address, flags));
            address += ARCH_PAGE_SIZE;
        }

        return {};
    }

    bool validate_readable_page(u64 address)
    {
        auto rc = MMU::get_flags(address);
        if (rc.has_error()) return false;
        return true;
    }

    bool validate_writable_page(u64 address)
    {
        auto rc = MMU::get_flags(address);
        if (rc.has_error()) return false;
        if (rc.release_value() & MMU::ReadWrite) return true;
        return false;
    }

    u64 free()
    {
        return free_mem;
    }

    u64 used()
    {
        return used_mem;
    }

    u64 reserved()
    {
        return reserved_mem;
    }

    u64 total()
    {
        return free_mem + used_mem + reserved_mem;
    }
}