feat/kernel: Added a physical page manager, has caching for single page alloc

.vscode/settings.json

@@ -2,6 +2,8 @@
     "files.associations": {
         "cstdio": "c",
         "stdarg.h": "c",
-        "idt.h": "c"
+        "idt.h": "c",
+        "limine.h": "c",
+        "stddef.h": "c"
     }
 }

kernel/src/boot/emk.h

@@ -0,0 +1,15 @@
+#ifndef EMK_H
+#define EMK_H
+
+#include <boot/limine.h>
+#include <stdint.h>
+
+extern uint64_t hhdm_offset;
+extern struct limine_memmap_response *memmap;
+
+#define HIGHER_HALF(ptr) ((void *)((uint64_t)ptr) + hhdm_offset)
+#define PHYSICAL(ptr) ((void *)((uint64_t)ptr) - hhdm_offset)
+
+#define BIT(x) (1ULL << (x))
+
+#endif // EMK_H

kernel/src/emk.c

@@ -1,5 +1,6 @@
 /* EMK 1.0 Copyright (c) 2025 Piraterna */
 #include <boot/limine.h>
+#include <boot/emk.h>
 #include <arch/cpu.h>
 #include <arch/io.h>
 #include <dev/serial.h>
@@ -7,11 +8,22 @@
 #include <util/log.h>
 #include <arch/gdt.h>
 #include <arch/idt.h>
+#include <sys/kpanic.h>
+#include <mm/pmm.h>
 
 __attribute__((used, section(".limine_requests"))) static volatile LIMINE_BASE_REVISION(3);
+__attribute__((used, section(".limine_requests"))) static volatile struct limine_memmap_request memmap_request = {
+    .id = LIMINE_MEMMAP_REQUEST,
+    .revision = 0};
+__attribute__((used, section(".limine_requests"))) static volatile struct limine_hhdm_request hhdm_request = {
+    .id = LIMINE_HHDM_REQUEST,
+    .revision = 0};
 __attribute__((used, section(".limine_requests_start"))) static volatile LIMINE_REQUESTS_START_MARKER;
 __attribute__((used, section(".limine_requests_end"))) static volatile LIMINE_REQUESTS_END_MARKER;
 
+uint64_t hhdm_offset = 0;
+struct limine_memmap_response *memmap = NULL;
+
 void emk_entry(void)
 {
     if (serial_init(COM1) != 0)
@@ -33,5 +45,30 @@ void emk_entry(void)
     idt_init();
     log_early("Initialized IDT");
 
+    if (!hhdm_request.response)
+    {
+        kpanic(NULL, "Failed to get HHDM request");
+    }
+
+    if (!memmap_request.response)
+    {
+        kpanic(NULL, "Failed to get memmap request");
+    }
+
+    memmap = memmap_request.response;
+    hhdm_offset = hhdm_request.response->offset;
+    log_early("HHDM Offset: %llx", hhdm_offset);
+    pmm_init();
+    log_early("Initialized PMM");
+
+    /* Test allocate a single physical page */
+    char *a = pmm_request_pages(1, true);
+    if (!a)
+        kpanic(NULL, "Failed to allocate single physical page");
+
+    *a = 32;
+    log_early("Allocated 1 physical page: %llx", (uint64_t)a);
+    pmm_release_pages(a, 1);
+
     hlt();
 }

kernel/src/lib/bitmap.h

@@ -0,0 +1,21 @@
+#ifndef BITMAP_H
+#define BITMAP_H
+
+#include <stdint.h>
+
+static inline void bitmap_set(uint8_t *bitmap, uint64_t bit)
+{
+    bitmap[bit / 8] |= 1 << (bit % 8);
+}
+
+static inline void bitmap_clear(uint8_t *bitmap, uint64_t bit)
+{
+    bitmap[bit / 8] &= ~(1 << (bit % 8));
+}
+
+static inline uint8_t bitmap_get(uint8_t *bitmap, uint64_t bit)
+{
+    return (bitmap[bit / 8] & (1 << (bit % 8))) != 0;
+}
+
+#endif // BITMAP_H

kernel/src/mm/pmm.c

@@ -0,0 +1,170 @@
+#include <mm/pmm.h>
+#include <boot/emk.h>
+#include <util/log.h>
+#include <arch/cpu.h>
+#include <util/align.h>
+#include <lib/string.h>
+#include <lib/bitmap.h>
+#include <sys/spinlock.h>
+
+#define PAGE_CACHE_SIZE 1024
+#define MIN_ALIGN PAGE_SIZE
+#define BITMAP_WORD_SIZE (sizeof(uint64_t) * 8)
+
+uint64_t bitmap_pages;
+uint64_t bitmap_size;
+uint8_t *bitmap;
+static uint64_t free_pages;
+static spinlock_t pmm_lock;
+static uint64_t page_cache[PAGE_CACHE_SIZE];
+static size_t cache_size;
+static size_t cache_index;
+
+static inline bool is_aligned(void *addr, size_t align)
+{
+    return ((uintptr_t)addr % align) == 0;
+}
+
+void pmm_init(void)
+{
+    spinlock_init(&pmm_lock);
+
+    uint64_t high = 0;
+    free_pages = 0;
+
+    for (uint64_t i = 0; i < memmap->entry_count; i++)
+    {
+        struct limine_memmap_entry *e = memmap->entries[i];
+        if (e->type == LIMINE_MEMMAP_USABLE)
+        {
+            uint64_t top = e->base + e->length;
+            if (top > high)
+                high = top;
+            free_pages += e->length / PAGE_SIZE;
+            log_early("Usable memory region: 0x%.16llx -> 0x%.16llx", e->base, e->base + e->length);
+        }
+    }
+
+    bitmap_pages = high / PAGE_SIZE;
+    bitmap_size = ALIGN_UP(bitmap_pages / 8, PAGE_SIZE);
+
+    for (uint64_t i = 0; i < memmap->entry_count; i++)
+    {
+        struct limine_memmap_entry *e = memmap->entries[i];
+        if (e->type == LIMINE_MEMMAP_USABLE && e->length >= bitmap_size)
+        {
+            bitmap = (uint8_t *)(e->base + hhdm_offset);
+            memset(bitmap, 0xFF, bitmap_size);
+            e->base += bitmap_size;
+            e->length -= bitmap_size;
+            free_pages -= bitmap_size / PAGE_SIZE;
+            break;
+        }
+    }
+
+    cache_size = PAGE_CACHE_SIZE;
+    cache_index = 0;
+    memset(page_cache, 0, sizeof(page_cache));
+
+    for (uint64_t i = 0; i < memmap->entry_count; i++)
+    {
+        struct limine_memmap_entry *e = memmap->entries[i];
+        if (e->type == LIMINE_MEMMAP_USABLE)
+        {
+            for (uint64_t j = e->base; j < e->base + e->length; j += PAGE_SIZE)
+            {
+                if ((j / PAGE_SIZE) < bitmap_pages)
+                {
+                    bitmap_clear(bitmap, j / PAGE_SIZE);
+                }
+            }
+        }
+    }
+}
+
+void *pmm_request_pages(size_t pages, bool higher_half)
+{
+    if (pages == 0 || pages > free_pages)
+        return NULL;
+
+    spinlock_acquire(&pmm_lock);
+
+    if (pages == 1 && cache_index > 0)
+    {
+        void *addr = (void *)(page_cache[--cache_index] * PAGE_SIZE);
+        bitmap_set(bitmap, (uint64_t)addr / PAGE_SIZE);
+        free_pages--;
+        spinlock_release(&pmm_lock);
+        return higher_half ? (void *)((uint64_t)addr + hhdm_offset) : addr;
+    }
+
+    uint64_t word_count = (bitmap_pages + BITMAP_WORD_SIZE - 1) / BITMAP_WORD_SIZE;
+    uint64_t *bitmap_words = (uint64_t *)bitmap;
+
+    for (uint64_t i = 0; i < word_count; i++)
+    {
+        if (bitmap_words[i] != UINT64_MAX)
+        {
+            uint64_t start_bit = i * BITMAP_WORD_SIZE;
+            uint64_t consecutive = 0;
+
+            for (uint64_t j = 0; j < BITMAP_WORD_SIZE && start_bit + j < bitmap_pages; j++)
+            {
+                if (!bitmap_get(bitmap, start_bit + j))
+                {
+                    if (++consecutive == pages)
+                    {
+                        for (uint64_t k = 0; k < pages; k++)
+                        {
+                            bitmap_set(bitmap, start_bit + j - pages + 1 + k);
+                        }
+                        free_pages -= pages;
+
+                        void *addr = (void *)((start_bit + j - pages + 1) * PAGE_SIZE);
+                        spinlock_release(&pmm_lock);
+                        return higher_half ? (void *)((uint64_t)addr + hhdm_offset) : addr;
+                    }
+                }
+                else
+                {
+                    consecutive = 0;
+                }
+            }
+        }
+    }
+
+    spinlock_release(&pmm_lock);
+    return NULL;
+}
+
+void pmm_release_pages(void *ptr, size_t pages)
+{
+    if (!ptr || !is_aligned(ptr, MIN_ALIGN))
+        return;
+
+    spinlock_acquire(&pmm_lock);
+
+    uint64_t start = ((uint64_t)ptr - (hhdm_offset * ((uint64_t)ptr >= hhdm_offset))) / PAGE_SIZE;
+
+    if (start + pages > bitmap_pages)
+    {
+        spinlock_release(&pmm_lock);
+        return;
+    }
+
+    for (size_t i = 0; i < pages; i++)
+    {
+        if (bitmap_get(bitmap, start + i))
+        {
+            bitmap_clear(bitmap, start + i);
+            free_pages++;
+
+            if (pages == 1 && cache_index < cache_size)
+            {
+                page_cache[cache_index++] = start;
+            }
+        }
+    }
+
+    spinlock_release(&pmm_lock);
+}

kernel/src/mm/pmm.h

@@ -0,0 +1,13 @@
+#ifndef PMM_H
+#define PMM_H
+
+#include <stddef.h>
+#include <stdbool.h>
+
+#define PAGE_SIZE 0x1000
+
+void pmm_init();
+void *pmm_request_pages(size_t pages, bool higher_half);
+void pmm_release_pages(void *ptr, size_t pages);
+
+#endif // PMM_H

kernel/src/sys/spinlock.h

@@ -0,0 +1,40 @@
+#ifndef SPINLOCK_H
+#define SPINLOCK_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+typedef struct
+{
+    volatile uint32_t lock; // 0 = unlocked, 1 = locked
+} spinlock_t;
+
+static inline void spinlock_init(spinlock_t *lock)
+{
+    lock->lock = 0;
+}
+
+static inline void spinlock_acquire(spinlock_t *lock)
+{
+    while (__atomic_test_and_set(&lock->lock, __ATOMIC_ACQUIRE))
+    {
+        asm volatile("pause" ::: "memory");
+    }
+}
+
+static inline void spinlock_release(spinlock_t *lock)
+{
+    __atomic_clear(&lock->lock, __ATOMIC_RELEASE);
+}
+
+static inline bool spinlock_try_acquire(spinlock_t *lock)
+{
+    return !__atomic_test_and_set(&lock->lock, __ATOMIC_ACQUIRE);
+}
+
+static inline bool spinlock_held(spinlock_t *lock)
+{
+    return __atomic_load_n(&lock->lock, __ATOMIC_RELAXED) != 0;
+}
+
+#endif // SPINLOCK_H

kernel/src/util/align.h

@@ -0,0 +1,10 @@
+#ifndef ALIGN_H
+#define ALIGN_H
+
+#define DIV_ROUND_UP(x, y) (((uint64_t)(x) + ((uint64_t)(y) - 1)) / (uint64_t)(y))
+#define ALIGN_UP(x, y) (DIV_ROUND_UP(x, y) * (uint64_t)(y))
+#define ALIGN_DOWN(x, y) (((uint64_t)(x) / (uint64_t)(y)) * (uint64_t)(y))
+
+#define IS_PAGE_ALIGNED(x) (((uintptr_t)(x) & (PAGE_SIZE - 1)) == 0)
+
+#endif // ALIGN_H