Luna/kernel/src/memory/KernelVM.cpp

#include "memory/KernelVM.h"
#include "arch/MMU.h"
#include <luna/Bitmap.h>

static const u64 KERNEL_VM_RANGE_START = 0xfffffffff0000000;

static Bitmap g_kernelvm_bitmap;

static u8 bitmap_memory[4096];

static const usize KERNEL_VM_RANGE_SIZE = (sizeof(bitmap_memory) * 8) * ARCH_PAGE_SIZE;

static const u64 KERNEL_VM_RANGE_END = KERNEL_VM_RANGE_SIZE + KERNEL_VM_RANGE_START;

static_assert(KERNEL_VM_RANGE_END == 0xfffffffff8000000);

static usize g_used_vm;

namespace KernelVM
{
    void init()
    {
        g_kernelvm_bitmap.initialize(bitmap_memory, sizeof(bitmap_memory));
        g_kernelvm_bitmap.clear(false);
    }

    Result<u64> alloc_one_page()
    {
        for (u64 index = 0; index < g_kernelvm_bitmap.size(); index++)
        {
            if (g_kernelvm_bitmap.get(index)) continue;
            g_kernelvm_bitmap.set(index, true);
            g_used_vm += ARCH_PAGE_SIZE;
            return KERNEL_VM_RANGE_START + (index * ARCH_PAGE_SIZE);
        }

        return err(ENOMEM);
    }

    bool find_several_pages_impl(usize count, u64& start_index)
    {
        u64 first_free_index = 0;
        u64 free_contiguous_pages = 0;
        for (u64 index = 0; index < g_kernelvm_bitmap.size(); index++)
        {
            if (g_kernelvm_bitmap.get(index))
            {
                free_contiguous_pages = 0;
                continue;
            }

            // At this point, we have a free page.

            if (!free_contiguous_pages) first_free_index = index;
            free_contiguous_pages++;

            // Found enough contiguous free pages!!
            if (free_contiguous_pages == count)
            {
                start_index = first_free_index;
                return true;
            }
        }

        return false;
    }

    Result<u64> alloc_several_pages(const usize count)
    {
        u64 start_index;
        if (find_several_pages_impl(count, start_index))
        {
            g_kernelvm_bitmap.clear_region(start_index, count, true);
            g_used_vm += ARCH_PAGE_SIZE * count;
            return KERNEL_VM_RANGE_START + (start_index * ARCH_PAGE_SIZE);
        }

        return err(ENOMEM);
    }

    Result<void> free_one_page(u64 address)
    {
        if (address < KERNEL_VM_RANGE_START) return err(EFAULT);

        u64 index = (address - KERNEL_VM_RANGE_START) / ARCH_PAGE_SIZE;

        if (index >= g_kernelvm_bitmap.size()) return err(EFAULT);

        g_kernelvm_bitmap.set(index, false);
        g_used_vm -= ARCH_PAGE_SIZE;

        return {};
    }

    Result<void> free_several_pages(u64 address, usize count)
    {
        if (address < KERNEL_VM_RANGE_START) return err(EFAULT);
        if (address + (count * ARCH_PAGE_SIZE) >= KERNEL_VM_RANGE_END) return err(EFAULT);

        u64 index = (address - KERNEL_VM_RANGE_START) / ARCH_PAGE_SIZE;

        g_kernelvm_bitmap.clear_region(index, count, false);
        g_used_vm -= ARCH_PAGE_SIZE * count;

        return {};
    }

    usize used()
    {
        return g_used_vm;
    }

    usize free()
    {
        return KERNEL_VM_RANGE_SIZE - g_used_vm;
    }
}