SUB-OS/mm/pmm.c

#include <mm/pmm.h>
#include <lib/bitmap.h>
#include <lib/string.h>
#include <kernel/printk.h>

#define MAX_PHYSICAL_PAGES (1024 * 1024) // 4 GB (1,048,576 4KB pages)
#define BITMAP_SIZE        (MAX_PHYSICAL_PAGES / 64)

static bitmap_word_t page_bitmap[BITMAP_SIZE];
static uint64_t total_pages = 0;
static uint64_t used_pages = 0;
static uint64_t total_memory_bytes = 0;
static uint64_t usable_memory_bytes = 0;

void pmm_init(void* memory_map, uint64_t memory_map_count) {
    // Initially mark all pages as reserved (1 in bitmap)
    memset(page_bitmap, 0xFF, sizeof(page_bitmap));
    total_pages = 0;
    used_pages = 0;
    total_memory_bytes = 0;
    usable_memory_bytes = 0;

    e820_entry_t* entries = (e820_entry_t*)memory_map;

    if (memory_map && memory_map_count > 0) {
        for (uint64_t i = 0; i < memory_map_count; i++) {
            uint64_t base = entries[i].base;
            uint64_t length = entries[i].length;
            uint32_t type = entries[i].type;

            total_memory_bytes += length;

            if (type == E820_TYPE_USABLE) {
                usable_memory_bytes += length;

                uint64_t start_page = base / PMM_PAGE_SIZE;
                uint64_t page_count = length / PMM_PAGE_SIZE;

                for (uint64_t p = 0; p < page_count; p++) {
                    uint64_t page = start_page + p;
                    if (page < MAX_PHYSICAL_PAGES) {
                        bitmap_clear(page_bitmap, page);
                        if (page >= total_pages) {
                            total_pages = page + 1;
                        }
                    }
                }
            }
        }
    }

    // Fallback if no E820 usable regions detected
    if (usable_memory_bytes == 0 || total_pages == 0) {
#if defined(__aarch64__) || defined(__arm__) || defined(__armv8i__)
        uint64_t dram_start = 0x40000000;
        uint64_t dram_size  = 128ULL * 1024 * 1024;
        uint64_t start_page = dram_start / PMM_PAGE_SIZE;
        uint64_t count_pages = dram_size / PMM_PAGE_SIZE;

        total_pages = start_page + count_pages;
        total_memory_bytes = dram_size;
        usable_memory_bytes = dram_size;

        for (uint64_t p = 0; p < count_pages; p++) {
            bitmap_clear(page_bitmap, start_page + p);
        }
#else
        total_pages = 32768; // 128 MB
        total_memory_bytes = 128ULL * 1024 * 1024;
        usable_memory_bytes = 128ULL * 1024 * 1024;
        for (uint64_t p = 0; p < total_pages; p++) {
            bitmap_clear(page_bitmap, p);
        }
#endif
    }

    // ALWAYS Reserve Kernel & Critical Bootloader/Page Tables Area
#if defined(__aarch64__) || defined(__arm__) || defined(__armv8i__)
    uint64_t dram_start_page = 0x40000000 / PMM_PAGE_SIZE;
    for (uint64_t p = dram_start_page; p < dram_start_page + 2048; p++) {
        bitmap_set(page_bitmap, p);
    }
#else
    // Reserve lower 8 MB on x86_64 (IVT, BDA, bootloader, GDT/IDT, PML4 page tables, kernel binary)
    size_t kernel_reserved_pages = (8 * 1024 * 1024) / PMM_PAGE_SIZE; // 2048 pages (8MB)
    for (size_t p = 0; p < kernel_reserved_pages; p++) {
        bitmap_set(page_bitmap, p);
    }
#endif

    // Count actual used pages (bits set in bitmap up to total_pages)
    used_pages = 0;
    for (uint64_t p = 0; p < total_pages; p++) {
        if (bitmap_test(page_bitmap, p)) {
            used_pages++;
        }
    }

    printk(KERN_INFO "PMM: Total Memory: %llu MB, Usable: %llu MB, Free Pages: %llu\n",
           total_memory_bytes / (1024 * 1024),
           usable_memory_bytes / (1024 * 1024),
           pmm_get_free_pages());
}

void* pmm_alloc_page(void) {
    for (uint64_t i = 0; i < total_pages; i++) {
        if (!bitmap_test(page_bitmap, i)) {
            bitmap_set(page_bitmap, i);
            used_pages++;
            return (void*)(i * PMM_PAGE_SIZE);
        }
    }
    return NULL; // Out of memory
}

void* pmm_alloc_pages(size_t count) {
    if (count == 0) return NULL;

    uint64_t consecutive_free = 0;
    uint64_t start_page = 0;

    for (uint64_t i = 0; i < total_pages; i++) {
        if (!bitmap_test(page_bitmap, i)) {
            if (consecutive_free == 0) {
                start_page = i;
            }
            consecutive_free++;
            if (consecutive_free == count) {
                // Found contiguous block, mark all as allocated
                for (uint64_t p = start_page; p < start_page + count; p++) {
                    bitmap_set(page_bitmap, p);
                }
                used_pages += count;
                return (void*)(start_page * PMM_PAGE_SIZE);
            }
        } else {
            consecutive_free = 0;
        }
    }

    return NULL; // Out of memory for contiguous block
}

void pmm_free_page(void* ptr) {
    if (!ptr) return;
    uint64_t page = (uint64_t)ptr / PMM_PAGE_SIZE;
    if (page < total_pages && bitmap_test(page_bitmap, page)) {
        bitmap_clear(page_bitmap, page);
        if (used_pages > 0) used_pages--;
    }
}

void pmm_free_pages(void* ptr, size_t count) {
    if (!ptr || count == 0) return;
    uint64_t start_page = (uint64_t)ptr / PMM_PAGE_SIZE;
    for (size_t i = 0; i < count; i++) {
        uint64_t page = start_page + i;
        if (page < total_pages && bitmap_test(page_bitmap, page)) {
            bitmap_clear(page_bitmap, page);
            if (used_pages > 0) used_pages--;
        }
    }
}

uint64_t pmm_get_total_memory(void) {
    return total_memory_bytes;
}

uint64_t pmm_get_usable_memory(void) {
    return usable_memory_bytes;
}

uint64_t pmm_get_total_pages(void) {
    return total_pages;
}

uint64_t pmm_get_free_pages(void) {
    return (total_pages > used_pages) ? (total_pages - used_pages) : 0;
}

uint64_t pmm_get_used_pages(void) {
    return used_pages;
}