Add basic paging. Only identity maps the bottom 4MB as a start.

Kernel/MemoryManager.cpp

@@ -0,0 +1,90 @@
+#include "MemoryManager.h"
+#include <AK/Assertions.h>
+#include <AK/kstdio.h>
+#include <AK/kmalloc.h>
+#include "i386.h"
+#include "StdLib.h"
+
+static MemoryManager* s_the;
+
+MemoryManager& MemoryManager::the()
+{
+    return *s_the;
+}
+
+MemoryManager::MemoryManager()
+{
+    m_pageDirectory = (dword*)0x5000;
+    m_pageTableZero = (dword*)0x6000;
+
+    initializePaging();
+}
+
+MemoryManager::~MemoryManager()
+{
+}
+
+void MemoryManager::initializePaging()
+{
+    static_assert(sizeof(MemoryManager::PageDirectoryEntry) == 4);
+    static_assert(sizeof(MemoryManager::PageTableEntry) == 4);
+    memset(m_pageTableZero, 0, 4096);
+    memset(m_pageDirectory, 0, 4096);
+
+    kprintf("MM: Page directory @ %p\n", m_pageDirectory);
+    kprintf("MM: Page table zero @ %p [0]=%x\n", m_pageTableZero, m_pageTableZero[0]);
+    // Build a basic PDB that identity maps the first 1MB.
+    identityMap(LinearAddress(0), 4 * MB);
+
+    asm volatile("movl %%eax, %%cr3"::"a"(m_pageDirectory));
+    asm volatile(
+        "movl %cr0, %eax\n"
+        "orl $0x80000001, %eax\n"
+        "movl %eax, %cr0\n"
+    );
+}
+
+auto MemoryManager::ensurePTE(LinearAddress linearAddress) -> PageTableEntry
+{
+    dword pageDirectoryIndex = (linearAddress.get() >> 22) & 0x3ff;
+    dword pageTableIndex = (linearAddress.get() >> 12) & 0x3ff;
+
+    PageDirectoryEntry pde = PageDirectoryEntry(&m_pageDirectory[pageDirectoryIndex]);
+    if (!pde.isPresent()) {
+        kprintf("PDE %u !present, allocating\n", pageDirectoryIndex);
+        if (pageDirectoryIndex == 0) {
+            pde.setPageTableBase((dword)m_pageTableZero);
+            pde.setUserAllowed(true);
+            pde.setPresent(true);
+            pde.setWritable(true);
+        } else {
+            // FIXME: We need an allocator!
+            ASSERT_NOT_REACHED();
+        }
+    }
+    return PageTableEntry(&pde.pageTableBase()[pageTableIndex]);
+}
+
+void MemoryManager::identityMap(LinearAddress linearAddress, size_t length)
+{
+    // FIXME: ASSERT(linearAddress is 4KB aligned);
+    for (dword offset = 0; offset < length; offset += 4096) {
+        auto pteAddress = linearAddress.offset(offset);
+        auto pte = ensurePTE(pteAddress);
+        pte.setPhysicalPageBase(pteAddress.get());
+        pte.setUserAllowed(true);
+        pte.setPresent(true);
+        pte.setWritable(true);
+        if (pteAddress.get() == 0x6023) {
+            kprintf("kek\n");
+            HANG;
+        }
+    }
+}
+
+void MemoryManager::initialize()
+{
+    s_the = new MemoryManager;
+}
+
+