Kernel: Move Memory/PageDirectory.{cpp,h} to arch-specific directory

The handling of page tables is very architecture specific, so belongs
in the Arch directory. Some parts were already architecture-specific,
however this commit moves the rest of the PageDirectory class into the
Arch directory.

While we're here the aarch64/PageDirectory.{h,cpp} files are updated to
be aarch64 specific, by renaming some members and removing x86_64
specific code.

Kernel/Arch/aarch64/PageDirectory.cpp

@@ -5,8 +5,17 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Singleton.h>
+#include <Kernel/Arch/CPU.h>
+#include <Kernel/Arch/PageDirectory.h>
 #include <Kernel/Arch/aarch64/ASM_wrapper.h>
-#include <Kernel/Memory/PageDirectory.h>
+#include <Kernel/InterruptDisabler.h>
+#include <Kernel/Memory/MemoryManager.h>
+#include <Kernel/Prekernel/Prekernel.h>
+#include <Kernel/Process.h>
+#include <Kernel/Random.h>
+#include <Kernel/Sections.h>
+#include <Kernel/Thread.h>
 
 namespace Kernel::Memory {
 
@@ -36,4 +45,68 @@ void activate_page_directory(PageDirectory const&, Thread*)
     TODO_AARCH64();
 }
 
+UNMAP_AFTER_INIT NonnullLockRefPtr<PageDirectory> PageDirectory::must_create_kernel_page_directory()
+{
+    return adopt_lock_ref_if_nonnull(new (nothrow) PageDirectory).release_nonnull();
+}
+
+ErrorOr<NonnullLockRefPtr<PageDirectory>> PageDirectory::try_create_for_userspace()
+{
+    auto directory = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) PageDirectory));
+
+    directory->m_root_table = TRY(MM.allocate_physical_page());
+
+    directory->m_directory_table = TRY(MM.allocate_physical_page());
+    auto kernel_pd_index = (kernel_mapping_base >> 30) & 0x1ffu;
+    for (size_t i = 0; i < kernel_pd_index; i++) {
+        directory->m_directory_pages[i] = TRY(MM.allocate_physical_page());
+    }
+
+    // Share the top 1 GiB of kernel-only mappings (>=kernel_mapping_base)
+    directory->m_directory_pages[kernel_pd_index] = MM.kernel_page_directory().m_directory_pages[kernel_pd_index];
+
+    {
+        InterruptDisabler disabler;
+        auto& table = *(PageDirectoryPointerTable*)MM.quickmap_page(*directory->m_root_table);
+        table.raw[0] = (FlatPtr)directory->m_directory_table->paddr().as_ptr() | TABLE_DESCRIPTOR;
+        MM.unquickmap_page();
+    }
+
+    {
+        InterruptDisabler disabler;
+        auto& table = *(PageDirectoryPointerTable*)MM.quickmap_page(*directory->m_directory_table);
+        for (size_t i = 0; i < sizeof(m_directory_pages) / sizeof(m_directory_pages[0]); i++) {
+            if (directory->m_directory_pages[i]) {
+                table.raw[i] = (FlatPtr)directory->m_directory_pages[i]->paddr().as_ptr() | PAGE_DESCRIPTOR;
+            }
+        }
+        MM.unquickmap_page();
+    }
+
+    register_page_directory(directory);
+    return directory;
+}
+
+PageDirectory::PageDirectory() = default;
+
+UNMAP_AFTER_INIT void PageDirectory::allocate_kernel_directory()
+{
+    // Adopt the page tables already set up by boot.S
+    dmesgln("MM: boot_pml4t @ {}", boot_pml4t);
+    m_root_table = PhysicalPage::create(boot_pml4t, MayReturnToFreeList::No);
+    dmesgln("MM: boot_pdpt @ {}", boot_pdpt);
+    dmesgln("MM: boot_pd0 @ {}", boot_pd0);
+    dmesgln("MM: boot_pd_kernel @ {}", boot_pd_kernel);
+    m_directory_table = PhysicalPage::create(boot_pdpt, MayReturnToFreeList::No);
+    m_directory_pages[0] = PhysicalPage::create(boot_pd0, MayReturnToFreeList::No);
+    m_directory_pages[(kernel_mapping_base >> 30) & 0x1ff] = PhysicalPage::create(boot_pd_kernel, MayReturnToFreeList::No);
+}
+
+PageDirectory::~PageDirectory()
+{
+    if (is_root_table_initialized()) {
+        deregister_page_directory(this);
+    }
+}
+
 }