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

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#include <BAN/Errors.h>
#include <kernel/MMU.h>
#include <kernel/kmalloc.h>
#include <kernel/Serial.h>
#include <string.h>
#define PRESENT (1 << 0)
#define READ_WRITE (1 << 1)
// bits 31-12 set
#define PAGE_MASK 0xfffff000
#define PAGE_SIZE 0x00001000
static MMU* s_instance = nullptr;
void MMU::Intialize()
{
ASSERT(s_instance == nullptr);
s_instance = new MMU();
}
MMU& MMU::Get()
{
ASSERT(s_instance);
return *s_instance;
}
static uint64_t* allocate_page_aligned_page()
{
uint64_t* page_directory = (uint64_t*)kmalloc(PAGE_SIZE, PAGE_SIZE);
ASSERT(page_directory);
ASSERT(((uintptr_t)page_directory % PAGE_SIZE) == 0);
memset(page_directory, 0, PAGE_SIZE);
return page_directory;
}
MMU::MMU()
{
m_page_descriptor_pointer_table = (uint64_t*)kmalloc(sizeof(uint64_t) * 4, 32);
ASSERT(m_page_descriptor_pointer_table);
ASSERT(((uintptr_t)m_page_descriptor_pointer_table % 32) == 0);
// create and zero out all page directories
for (int i = 0; i < 4; i++)
{
uint64_t* page_directory = allocate_page_aligned_page();
m_page_descriptor_pointer_table[i] = (uint64_t)page_directory | PRESENT;
}
// create and identity map first 4 MiB
uint64_t* page_directory1 = (uint64_t*)(m_page_descriptor_pointer_table[0] & PAGE_MASK);
for (uint64_t i = 0; i < 2; i++)
{
uint64_t* page_table = allocate_page_aligned_page();
for (uint64_t j = 0; j < 512; j++)
page_table[j] = (i << 21) | (j << 12) | READ_WRITE | PRESENT;
page_directory1[i] = (uint64_t)page_table | READ_WRITE | 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_table1[0] = 0;
// reload this new pdpt
asm volatile("movl %0, %%cr3" :: "r"(m_page_descriptor_pointer_table));
}
void MMU::AllocatePage(uintptr_t address)
{
uint32_t pdpte = (address & 0xC0000000) >> 30;
uint32_t pde = (address & 0x3FE00000) >> 21;
uint32_t pte = (address & 0x001FF000) >> 12;
ASSERT(pdpte < 4);
uint64_t* page_directory = (uint64_t*)(m_page_descriptor_pointer_table[pdpte] & PAGE_MASK);
if (!(page_directory[pde] & PRESENT))
{
uint64_t* page_table = allocate_page_aligned_page();
page_directory[pde] = (uint64_t)page_table | READ_WRITE | PRESENT;
}
uint64_t* page_table = (uint64_t*)(page_directory[pde] & PAGE_MASK);
page_table[pte] = (address & PAGE_MASK) | READ_WRITE | PRESENT;
asm volatile("invlpg (%0)" :: "r"(address & PAGE_MASK) : "memory");
}
void MMU::AllocateRange(uintptr_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)
AllocatePage(page);
}