89 lines
2.2 KiB
C
89 lines
2.2 KiB
C
#include "pmm.h"
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#include "../arch/arch.h"
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#include <stddef.h>
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#include <stdio.h>
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#include <string.h>
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#define BITMAP_SIZE 32768 // Supports up to 1GB of RAM
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#define USABLE_REGION_SIZE 32
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static uint8_t page_bitmap[BITMAP_SIZE];
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static uint64_t total_pages = 0;
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static uint64_t free_pages = 0;
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void pmm_init()
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{
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memset(page_bitmap, 0xFF, BITMAP_SIZE);
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for (size_t i = 0; i < memory_map.num_regions; i++)
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{
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memory_region_t region = memory_map.regions[i];
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uint64_t start_page = region.base_address / PAGE_SIZE;
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uint64_t num_pages = region.length / PAGE_SIZE;
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for (uint64_t page = start_page; page < start_page + num_pages; page++)
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{
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if (page < BITMAP_SIZE * 8)
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{
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page_bitmap[page / 8] &= ~(1 << (page % 8));
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free_pages++;
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total_pages++;
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}
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else
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{
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printf("System has more ram than the bitmap allows!\n");
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break;
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}
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}
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}
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// Reserve first 64MB which is reserved by boot code
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for (uint64_t page = 0; page < (64 * 1024 * 1024) / PAGE_SIZE; page++)
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{
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if (page < BITMAP_SIZE * 8)
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{
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if (!(page_bitmap[page / 8] & (1 << (page % 8))))
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{
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page_bitmap[page / 8] |= (1 << (page % 8));
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free_pages--;
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}
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}
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}
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}
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// Returns the address of first free physical page
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uint64_t pmm_alloc_page()
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{
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for (size_t i = 0; i < BITMAP_SIZE; i++)
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{
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if (page_bitmap[i] != 0xFF)
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{
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for (int bit = 0; bit < 8; bit++)
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{
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if (!(page_bitmap[i] & (1 << bit)))
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{
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page_bitmap[i] |= (1 << bit);
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free_pages--;
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return ((i * 8 + bit) * PAGE_SIZE);
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}
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}
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}
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}
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return 0;
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}
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// Frees the physical page at the specified address
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void pmm_free_page(uint64_t addr)
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{
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uint64_t page = addr / PAGE_SIZE;
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if (page < BITMAP_SIZE * 8)
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{
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if (page_bitmap[page / 8] & (1 << (page % 8)))
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{
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page_bitmap[page / 8] &= ~(1 << (page % 8));
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free_pages++;
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}
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}
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} |