banan-os/kernel/arch/i386/MMU.cpp

#include <BAN/Errors.h>
#include <kernel/Debug.h>
#include <kernel/Memory/MMU.h>
#include <kernel/Memory/kmalloc.h>

#include <string.h>

#define MMU_DEBUG_PRINT 0

// bits 31-12 set
#define PAGE_MASK  0xfffff000
#define FLAGS_MASK 0x00000fff

namespace Kernel
{

	static MMU* s_instance = nullptr;

	void MMU::initialize()
	{
		ASSERT(s_instance == nullptr);
		s_instance = new MMU();
		ASSERT(s_instance);
		s_instance->initialize_kernel();
		s_instance->load();
	}

	MMU& MMU::get()
	{
		ASSERT(s_instance);
		return *s_instance;
	}

	static uint64_t* allocate_page_aligned_page()
	{
		uint64_t* page = (uint64_t*)kmalloc(PAGE_SIZE, PAGE_SIZE);
		ASSERT(page);
		ASSERT(((uintptr_t)page % PAGE_SIZE) == 0);
		memset(page, 0, PAGE_SIZE);
		return page;
	}

	void MMU::initialize_kernel()
	{
		m_highest_paging_struct = (uint64_t*)kmalloc(sizeof(uint64_t) * 4, 32);
		ASSERT(m_highest_paging_struct);
		ASSERT(((uintptr_t)m_highest_paging_struct % 32) == 0);

		// allocate all page directories
		for (int i = 0; i < 4; i++)
		{
			uint64_t* page_directory = allocate_page_aligned_page();
			m_highest_paging_struct[i] = (uint64_t)page_directory | Flags::Present;
		}

		// FIXME: We should just identity map until g_kernel_end

		// create and identity map first 6 MiB
		uint64_t* page_directory1 = (uint64_t*)(m_highest_paging_struct[0] & PAGE_MASK);
		for (uint64_t i = 0; i < 3; i++)
		{
			uint64_t* page_table = allocate_page_aligned_page();
			for (uint64_t j = 0; j < 512; j++)
				page_table[j] = (i << 21) | (j << 12) | Flags::ReadWrite | Flags::Present;

			page_directory1[i] = (uint64_t)page_table | Flags::ReadWrite | Flags::Present;
		}

		// dont map first page (0 -> 4 KiB) so that nullptr dereference
		// causes page fault :)
		uint64_t* page_table1 = (uint64_t*)(page_directory1[0] & PAGE_MASK);
		page_table1[0] = 0;
	}

	MMU::MMU()
	{
		if (s_instance == nullptr)
			return;
		
		// Here we copy the s_instances paging structs since they are
		// global for every process

		uint64_t* global_pdpt = s_instance->m_highest_paging_struct;

		uint64_t* pdpt = (uint64_t*)kmalloc(sizeof(uint64_t) * 4, 32);
		ASSERT(pdpt);
		
		for (uint32_t pdpte = 0; pdpte < 4; pdpte++)
		{
			if (!(global_pdpt[pdpte] & Flags::Present))
				continue;

			uint64_t* global_pd = (uint64_t*)(global_pdpt[pdpte] & PAGE_MASK);

			uint64_t* pd = allocate_page_aligned_page();
			pdpt[pdpte] = (uint64_t)pd | (global_pdpt[pdpte] & ~PAGE_MASK);

			for (uint32_t pde = 0; pde < 512; pde++)
			{
				if (!(global_pd[pde] & Flags::Present))
					continue;

				uint64_t* global_pt = (uint64_t*)(global_pd[pde] & PAGE_MASK);

				uint64_t* pt = allocate_page_aligned_page();
				pd[pde] = (uint64_t)pt | (global_pd[pde] & ~PAGE_MASK);

				memcpy(pt, global_pt, PAGE_SIZE);
			}
		}

		m_highest_paging_struct = pdpt;
	}

	MMU::~MMU()
	{
		uint64_t* pdpt = m_highest_paging_struct;
		for (uint32_t pdpte = 0; pdpte < 512; pdpte++)
		{
			if (!(pdpt[pdpte] & Flags::Present))
				continue;
			uint64_t* pd = (uint64_t*)(pdpt[pdpte] & PAGE_MASK);
			for (uint32_t pde = 0; pde < 512; pde++)
			{
				if (!(pd[pde] & Flags::Present))
					continue;
				kfree((void*)(pd[pde] & PAGE_MASK));
			}
			kfree(pd);
		}
		kfree(pdpt);
	}

	void MMU::load()
	{
		asm volatile("movl %0, %%cr3" :: "r"(m_highest_paging_struct));
	}

	void MMU::map_page_at(paddr_t paddr, vaddr_t vaddr, uint8_t flags)
	{
	#if MMU_DEBUG_PRINT
		dprintln("AllocatePage(0x{8H})", address);
	#endif
		ASSERT(flags & Flags::Present);

		ASSERT(!(paddr & ~PAGE_MASK));
		ASSERT(!(vaddr & ~PAGE_MASK));

		uint32_t pdpte = (vaddr & 0xC0000000) >> 30;
		uint32_t pde   = (vaddr & 0x3FE00000) >> 21;
		uint32_t pte   = (vaddr & 0x001FF000) >> 12;

		uint64_t* page_directory = (uint64_t*)(m_highest_paging_struct[pdpte] & PAGE_MASK);
		if (!(page_directory[pde] & Flags::Present))
		{
			uint64_t* page_table = allocate_page_aligned_page();
			page_directory[pde] = (uint64_t)page_table;
		}
		page_directory[pde] |= flags;

		uint64_t* page_table = (uint64_t*)(page_directory[pde] & PAGE_MASK);
		page_table[pte] = paddr | flags;
	}

	void MMU::identity_map_page(paddr_t address, uint8_t flags)
	{
		address &= PAGE_MASK;
		map_page_at(address, address, flags);
	}

	void MMU::identity_map_range(paddr_t address, ptrdiff_t size, uint8_t flags)
	{
		paddr_t s_page = address & PAGE_MASK;
		paddr_t e_page = (address + size - 1) & PAGE_MASK;
		for (paddr_t page = s_page; page <= e_page; page += PAGE_SIZE)
			identity_map_page(page, flags);
	}

	void MMU::unmap_page(vaddr_t address)
	{
	#if MMU_DEBUG_PRINT
		dprintln("UnAllocatePage(0x{8H})", address & PAGE_MASK);
	#endif

		uint32_t pdpte = (address & 0xC0000000) >> 30;
		uint32_t pde   = (address & 0x3FE00000) >> 21;
		uint32_t pte   = (address & 0x001FF000) >> 12;

		uint64_t* page_directory = (uint64_t*)(m_highest_paging_struct[pdpte] & PAGE_MASK);
		if (!(page_directory[pde] & Flags::Present))
			return;

		uint64_t* page_table = (uint64_t*)(page_directory[pde] & PAGE_MASK);
		if (!(page_table[pte] & Flags::Present))
			return;

		page_table[pte] = 0;

		// TODO: Unallocate the page table if this was the only allocated page
	}

	void MMU::unmap_range(vaddr_t address, ptrdiff_t size)
	{
		uintptr_t s_page = address & PAGE_MASK;
		uintptr_t e_page = (address + size - 1) & PAGE_MASK;
		for (uintptr_t page = s_page; page <= e_page; page += PAGE_SIZE)
			unmap_page(page);
	}

	uint8_t MMU::get_page_flags(vaddr_t address) const
	{
		uint32_t pdpte = (address & 0xC0000000) >> 30;
		uint32_t pde   = (address & 0x3FE00000) >> 21;
		uint32_t pte   = (address & 0x001FF000) >> 12;

		uint64_t* page_directory = (uint64_t*)(m_highest_paging_struct[pdpte] & PAGE_MASK);
		if (!(page_directory[pde] & Flags::Present))
			return 0;

		uint64_t* page_table = (uint64_t*)(page_directory[pde] & PAGE_MASK);
		if (!(page_table[pte] & Flags::Present))
			return 0;

		return page_table[pte] & FLAGS_MASK;
	}

}