forked from Bananymous/banan-os
126 lines
3.5 KiB
C++
126 lines
3.5 KiB
C++
#include <BAN/Errors.h>
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#include <kernel/MMU.h>
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#include <kernel/kmalloc.h>
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#include <kernel/Serial.h>
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#include <string.h>
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#define PRESENT (1 << 0)
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#define READ_WRITE (1 << 1)
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// bits 31-12 set
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#define PAGE_MASK 0xfffff000
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#define PAGE_SIZE 0x00001000
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static MMU* s_instance = nullptr;
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void MMU::Intialize()
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{
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ASSERT(s_instance == nullptr);
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s_instance = new MMU();
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}
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MMU& MMU::Get()
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{
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ASSERT(s_instance);
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return *s_instance;
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}
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static uint64_t* allocate_page_aligned_page()
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{
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uint64_t* page_directory = (uint64_t*)kmalloc(PAGE_SIZE, PAGE_SIZE);
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ASSERT(page_directory);
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ASSERT(((uintptr_t)page_directory % PAGE_SIZE) == 0);
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memset(page_directory, 0, PAGE_SIZE);
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return page_directory;
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}
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MMU::MMU()
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{
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m_page_descriptor_pointer_table = (uint64_t*)kmalloc(sizeof(uint64_t) * 4, 32);
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ASSERT(m_page_descriptor_pointer_table);
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ASSERT(((uintptr_t)m_page_descriptor_pointer_table % 32) == 0);
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// create and zero out all page directories
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for (int i = 0; i < 4; i++)
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{
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uint64_t* page_directory = allocate_page_aligned_page();
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m_page_descriptor_pointer_table[i] = (uint64_t)page_directory | PRESENT;
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}
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// create and identity map first 4 MiB
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uint64_t* page_directory1 = (uint64_t*)(m_page_descriptor_pointer_table[0] & PAGE_MASK);
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for (uint64_t i = 0; i < 2; i++)
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{
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uint64_t* page_table = allocate_page_aligned_page();
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for (uint64_t j = 0; j < 512; j++)
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page_table[j] = (i << 21) | (j << 12) | READ_WRITE | PRESENT;
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page_directory1[i] = (uint64_t)page_table | READ_WRITE | PRESENT;
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}
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// dont map first page (0 -> 4 KiB) so that nullptr dereference
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// causes page fault :)
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uint64_t* page_table1 = (uint64_t*)page_directory1[0];
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page_table1[0] = 0;
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// reload this new pdpt
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asm volatile("movl %0, %%cr3" :: "r"(m_page_descriptor_pointer_table));
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}
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void MMU::AllocatePage(uintptr_t address)
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{
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uint32_t pdpte = (address & 0xC0000000) >> 30;
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uint32_t pde = (address & 0x3FE00000) >> 21;
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uint32_t pte = (address & 0x001FF000) >> 12;
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ASSERT(pdpte < 4);
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uint64_t* page_directory = (uint64_t*)(m_page_descriptor_pointer_table[pdpte] & PAGE_MASK);
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if (!(page_directory[pde] & PRESENT))
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{
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uint64_t* page_table = allocate_page_aligned_page();
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page_directory[pde] = (uint64_t)page_table | READ_WRITE | PRESENT;
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}
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uint64_t* page_table = (uint64_t*)(page_directory[pde] & PAGE_MASK);
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page_table[pte] = (address & PAGE_MASK) | READ_WRITE | PRESENT;
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asm volatile("invlpg (%0)" :: "r"(address & PAGE_MASK) : "memory");
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}
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void MMU::AllocateRange(uintptr_t address, ptrdiff_t size)
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{
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uintptr_t s_page = address & PAGE_MASK;
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uintptr_t e_page = (address + size - 1) & PAGE_MASK;
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for (uintptr_t page = s_page; page <= e_page; page += PAGE_SIZE)
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AllocatePage(page);
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}
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void MMU::UnAllocatePage(uintptr_t address)
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{
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uint32_t pdpte = (address & 0xC0000000) >> 30;
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uint32_t pde = (address & 0x3FE00000) >> 21;
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uint32_t pte = (address & 0x001FF000) >> 12;
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uint64_t* page_directory = (uint64_t*)(m_page_descriptor_pointer_table[pdpte] & PAGE_MASK);
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ASSERT(page_directory[pde] & PRESENT);
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uint64_t* page_table = (uint64_t*)(page_directory[pde] & PAGE_MASK);
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ASSERT(page_table[pte] & PRESENT);
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page_table[pte] = 0;
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// TODO: Unallocate the page table if this was the only allocated page
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asm volatile("invlpg (%0)" :: "r"(address & PAGE_MASK) : "memory");
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}
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void MMU::UnAllocateRange(uintptr_t address, ptrdiff_t size)
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{
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uintptr_t s_page = address & PAGE_MASK;
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uintptr_t e_page = (address + size - 1) & PAGE_MASK;
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for (uintptr_t page = s_page; page <= e_page; page += PAGE_SIZE)
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UnAllocatePage(page);
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}
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