Kernel: Rename Kernel/VM/ to Kernel/Memory/

This directory isn't just about virtual memory, it's about all kinds
of memory management.

Kernel/Memory/PageDirectory.h

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <AK/RefCounted.h>
+#include <AK/RefPtr.h>
+#include <Kernel/Forward.h>
+#include <Kernel/Memory/PhysicalPage.h>
+#include <Kernel/Memory/RangeAllocator.h>
+
+namespace Kernel {
+
+class PageDirectory : public RefCounted<PageDirectory> {
+    friend class MemoryManager;
+
+public:
+    static RefPtr<PageDirectory> try_create_for_userspace(RangeAllocator const* parent_range_allocator = nullptr);
+    static NonnullRefPtr<PageDirectory> must_create_kernel_page_directory();
+    static RefPtr<PageDirectory> find_by_cr3(FlatPtr);
+
+    ~PageDirectory();
+
+    void allocate_kernel_directory();
+
+    FlatPtr cr3() const
+    {
+#if ARCH(X86_64)
+        return m_pml4t->paddr().get();
+#else
+        return m_directory_table->paddr().get();
+#endif
+    }
+
+    RangeAllocator& range_allocator() { return m_range_allocator; }
+    const RangeAllocator& range_allocator() const { return m_range_allocator; }
+
+    RangeAllocator& identity_range_allocator() { return m_identity_range_allocator; }
+
+    Space* space() { return m_space; }
+    const Space* space() const { return m_space; }
+
+    void set_space(Badge<Space>, Space& space) { m_space = &space; }
+
+    RecursiveSpinLock& get_lock() { return m_lock; }
+
+private:
+    PageDirectory();
+
+    Space* m_space { nullptr };
+    RangeAllocator m_range_allocator;
+    RangeAllocator m_identity_range_allocator;
+#if ARCH(X86_64)
+    RefPtr<PhysicalPage> m_pml4t;
+#endif
+    RefPtr<PhysicalPage> m_directory_table;
+#if ARCH(X86_64)
+    RefPtr<PhysicalPage> m_directory_pages[512];
+#else
+    RefPtr<PhysicalPage> m_directory_pages[4];
+#endif
+    HashMap<FlatPtr, RefPtr<PhysicalPage>> m_page_tables;
+    RecursiveSpinLock m_lock;
+};
+
+}