starting work on page tables

kernel/src/paging/PageFrameAllocator.cpp

@@ -0,0 +1,139 @@
+#include "PageFrameAllocator.h"
+
+uint64_t freeMemory;
+uint64_t reservedMemory;
+uint64_t usedMemory;
+bool Initialized = false;
+
+void PageFrameAllocator::ReadEFIMemoryMap(EFI_MEMORY_DESCRIPTOR* mMap, size_t mMapSize, size_t mMapDescSize){
+    if (Initialized) return;
+
+    Initialized = true;
+
+    uint64_t mMapEntries = mMapSize / mMapDescSize;
+
+    void* largestFreeMemSeg = NULL;
+    size_t largestFreeMemSegSize = 0;
+
+    for (int i = 0; i < mMapEntries; i++) {
+        EFI_MEMORY_DESCRIPTOR* desc = (EFI_MEMORY_DESCRIPTOR*)((uint64_t)mMap + (i * mMapDescSize));
+        if (desc->type == 7) {
+            if (desc -> numPages * 4096 > largestFreeMemSegSize) {
+                largestFreeMemSeg = desc-> physAddr;
+                largestFreeMemSegSize = desc -> numPages * 4096;
+            }
+        }
+    }
+
+    uint64_t memorySize = GetMemorySize(mMap, mMapEntries, mMapDescSize);
+    freeMemory = memorySize;
+    uint64_t bitmapSize = memorySize / 4096 / 8 + 1;
+
+    InitBitmap(bitmapSize, largestFreeMemSeg);
+
+    // lock pages of bitmap
+	LockPages(&PageBitmap, PageBitmap.Size / 4096 + 1);
+
+    //reserve pages of unsable/reserverd memory
+	for (int i = 0; i < mMapEntries; i++) {
+        EFI_MEMORY_DESCRIPTOR* desc = (EFI_MEMORY_DESCRIPTOR*)((uint64_t)mMap + (i * mMapDescSize));
+        if (desc->type != 7) { // not efiConventionalMemory
+			ReservePages(desc->physAddr, desc->numPages);
+		}
+	}
+}
+
+void PageFrameAllocator::InitBitmap(size_t bitmapSize, void* bufferAddress){
+    PageBitmap.Size = bitmapSize;
+    PageBitmap.Buffer = (uint8_t*)bufferAddress;
+    for (int i = 0; i < bitmapSize; i++){
+        *(uint8_t*)(PageBitmap.Buffer + i) = 0; 
+    }
+}
+
+void PageFrameAllocator::FreePage(void* address) {
+	uint64_t index = (uint64_t)address / 4096;
+	if (PageBitmap[index] == false) return; // page is already free
+
+	// free page in bitmap
+	PageBitmap.Set(index, false);
+	freeMemory += 4096;
+	usedMemory -= 4096;
+}
+
+void PageFrameAllocator::FreePages(void* address, uint64_t pageCount) {
+	for (int t = 0; t < pageCount; t++) {
+		FreePage((void*)((uint64_t)address + (t * 4096)));
+	}
+}
+
+void PageFrameAllocator::LockPage(void* address) {
+	uint64_t index = (uint64_t)address / 4096;
+	if (PageBitmap[index] == true) return; // page is already locked
+
+	// lock page in bitmap
+	PageBitmap.Set(index, true);
+	freeMemory -= 4096;
+	usedMemory += 4096;
+}
+
+void PageFrameAllocator::LockPages(void* address, uint64_t pageCount) {
+	for (int t = 0; t < pageCount; t++) {
+		LockPage((void*)((uint64_t)address + (t * 4096)));
+	}
+}
+
+void PageFrameAllocator::UnreservePage(void* address) {
+	uint64_t index = (uint64_t)address / 4096;
+	if (PageBitmap[index] == false) return; // page is already free
+
+	// free page in bitmap
+	PageBitmap.Set(index, false);
+	freeMemory += 4096;
+	reservedMemory -= 4096;
+}
+
+void PageFrameAllocator::UnreservePages(void* address, uint64_t pageCount) {
+	for (int t = 0; t < pageCount; t++) {
+		UnreservePage((void*)((uint64_t)address + (t * 4096)));
+	}
+}
+
+void PageFrameAllocator::ReservePage(void* address) {
+	uint64_t index = (uint64_t)address / 4096;
+	if (PageBitmap[index] == true) return; // page is already locked
+
+	// lock page in bitmap
+	PageBitmap.Set(index, true);
+	freeMemory -= 4096;
+	reservedMemory += 4096;
+}
+
+void PageFrameAllocator::ReservePages(void* address, uint64_t pageCount) {
+	for (int t = 0; t < pageCount; t++) {
+		ReservePage((void*)((uint64_t)address + (t * 4096)));
+	}
+}
+
+void* PageFrameAllocator::RequestPage() {
+	for (uint64_t index = 0; index < PageBitmap.Size * 8; index++) {
+		if (PageBitmap[index] == true) continue;
+
+		LockPage((void*)(index * 4096));
+		return (void*)(index * 4096);
+	}
+
+	return NULL; // page frame swap to file
+}
+
+uint64_t PageFrameAllocator::GetFreeRAM() {
+	return freeMemory;
+}
+
+uint64_t PageFrameAllocator::GetUsedRAM() {
+	return usedMemory;
+}
+
+uint64_t PageFrameAllocator::GetReservedRAM() {
+	return reservedMemory;
+}