ladybird/Kernel/Memory/MemoryManager.cpp

/*
 * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Assertions.h>
#include <AK/StringView.h>
#include <Kernel/Arch/CPU.h>
#include <Kernel/Arch/PageDirectory.h>
#include <Kernel/Arch/PageFault.h>
#include <Kernel/Arch/RegisterState.h>
#include <Kernel/BootInfo.h>
#include <Kernel/FileSystem/Inode.h>
#include <Kernel/Heap/kmalloc.h>
#include <Kernel/InterruptDisabler.h>
#include <Kernel/KSyms.h>
#include <Kernel/Memory/AnonymousVMObject.h>
#include <Kernel/Memory/MemoryManager.h>
#include <Kernel/Memory/PhysicalRegion.h>
#include <Kernel/Memory/SharedInodeVMObject.h>
#include <Kernel/Multiboot.h>
#include <Kernel/Panic.h>
#include <Kernel/Prekernel/Prekernel.h>
#include <Kernel/Process.h>
#include <Kernel/Sections.h>
#include <Kernel/StdLib.h>

extern u8 start_of_kernel_image[];
extern u8 end_of_kernel_image[];
extern u8 start_of_kernel_text[];
extern u8 start_of_kernel_data[];
extern u8 end_of_kernel_bss[];
extern u8 start_of_ro_after_init[];
extern u8 end_of_ro_after_init[];
extern u8 start_of_unmap_after_init[];
extern u8 end_of_unmap_after_init[];
extern u8 start_of_kernel_ksyms[];
extern u8 end_of_kernel_ksyms[];

extern multiboot_module_entry_t multiboot_copy_boot_modules_array[16];
extern size_t multiboot_copy_boot_modules_count;

namespace Kernel::Memory {

ErrorOr<FlatPtr> page_round_up(FlatPtr x)
{
    if (x > (explode_byte(0xFF) & ~0xFFF)) {
        return Error::from_errno(EINVAL);
    }
    return (((FlatPtr)(x)) + PAGE_SIZE - 1) & (~(PAGE_SIZE - 1));
}

// NOTE: We can NOT use Singleton for this class, because
// MemoryManager::initialize is called *before* global constructors are
// run. If we do, then Singleton would get re-initialized, causing
// the memory manager to be initialized twice!
static MemoryManager* s_the;

MemoryManager& MemoryManager::the()
{
    return *s_the;
}

bool MemoryManager::is_initialized()
{
    return s_the != nullptr;
}

static UNMAP_AFTER_INIT VirtualRange kernel_virtual_range()
{
#if ARCH(AARCH64)
    // NOTE: This is not the same as x86_64, because the aarch64 kernel currently doesn't use the pre-kernel.
    return VirtualRange { VirtualAddress(kernel_mapping_base), KERNEL_PD_END - kernel_mapping_base };
#else
    size_t kernel_range_start = kernel_mapping_base + 2 * MiB; // The first 2 MiB are used for mapping the pre-kernel
    return VirtualRange { VirtualAddress(kernel_range_start), KERNEL_PD_END - kernel_range_start };
#endif
}

MemoryManager::GlobalData::GlobalData()
    : region_tree(kernel_virtual_range())
{
}

UNMAP_AFTER_INIT MemoryManager::MemoryManager()
{
    s_the = this;

    parse_memory_map();
    activate_kernel_page_directory(kernel_page_directory());
    protect_kernel_image();

    // We're temporarily "committing" to two pages that we need to allocate below
    auto committed_pages = commit_physical_pages(2).release_value();

    m_shared_zero_page = committed_pages.take_one();

    // We're wasting a page here, we just need a special tag (physical
    // address) so that we know when we need to lazily allocate a page
    // that we should be drawing this page from the committed pool rather
    // than potentially failing if no pages are available anymore.
    // By using a tag we don't have to query the VMObject for every page
    // whether it was committed or not
    m_lazy_committed_page = committed_pages.take_one();
}

UNMAP_AFTER_INIT MemoryManager::~MemoryManager() = default;

UNMAP_AFTER_INIT void MemoryManager::protect_kernel_image()
{
    SpinlockLocker page_lock(kernel_page_directory().get_lock());
    // Disable writing to the kernel text and rodata segments.
    for (auto const* i = start_of_kernel_text; i < start_of_kernel_data; i += PAGE_SIZE) {
        auto& pte = *ensure_pte(kernel_page_directory(), VirtualAddress(i));
        pte.set_writable(false);
    }
    if (Processor::current().has_nx()) {
        // Disable execution of the kernel data, bss and heap segments.
        for (auto const* i = start_of_kernel_data; i < end_of_kernel_image; i += PAGE_SIZE) {
            auto& pte = *ensure_pte(kernel_page_directory(), VirtualAddress(i));
            pte.set_execute_disabled(true);
        }
    }
}

UNMAP_AFTER_INIT void MemoryManager::unmap_prekernel()
{
    SpinlockLocker page_lock(kernel_page_directory().get_lock());

    auto start = start_of_prekernel_image.page_base().get();
    auto end = end_of_prekernel_image.page_base().get();

    for (auto i = start; i <= end; i += PAGE_SIZE)
        release_pte(kernel_page_directory(), VirtualAddress(i), i == end ? IsLastPTERelease::Yes : IsLastPTERelease::No);
    flush_tlb(&kernel_page_directory(), VirtualAddress(start), (end - start) / PAGE_SIZE);
}

UNMAP_AFTER_INIT void MemoryManager::protect_readonly_after_init_memory()
{
    SpinlockLocker page_lock(kernel_page_directory().get_lock());
    // Disable writing to the .ro_after_init section
    for (auto i = (FlatPtr)&start_of_ro_after_init; i < (FlatPtr)&end_of_ro_after_init; i += PAGE_SIZE) {
        auto& pte = *ensure_pte(kernel_page_directory(), VirtualAddress(i));
        pte.set_writable(false);
        flush_tlb(&kernel_page_directory(), VirtualAddress(i));
    }
}

void MemoryManager::unmap_text_after_init()
{
    SpinlockLocker page_lock(kernel_page_directory().get_lock());

    auto start = page_round_down((FlatPtr)&start_of_unmap_after_init);
    auto end = page_round_up((FlatPtr)&end_of_unmap_after_init).release_value_but_fixme_should_propagate_errors();

    // Unmap the entire .unmap_after_init section
    for (auto i = start; i < end; i += PAGE_SIZE) {
        auto& pte = *ensure_pte(kernel_page_directory(), VirtualAddress(i));
        pte.clear();
        flush_tlb(&kernel_page_directory(), VirtualAddress(i));
    }

    dmesgln("Unmapped {} KiB of kernel text after init! :^)", (end - start) / KiB);
}

UNMAP_AFTER_INIT void MemoryManager::protect_ksyms_after_init()
{
    SpinlockLocker page_lock(kernel_page_directory().get_lock());

    auto start = page_round_down((FlatPtr)start_of_kernel_ksyms);
    auto end = page_round_up((FlatPtr)end_of_kernel_ksyms).release_value_but_fixme_should_propagate_errors();

    for (auto i = start; i < end; i += PAGE_SIZE) {
        auto& pte = *ensure_pte(kernel_page_directory(), VirtualAddress(i));
        pte.set_writable(false);
        flush_tlb(&kernel_page_directory(), VirtualAddress(i));
    }

    dmesgln("Write-protected kernel symbols after init.");
}

IterationDecision MemoryManager::for_each_physical_memory_range(Function<IterationDecision(PhysicalMemoryRange const&)> callback)
{
    return m_global_data.with([&](auto& global_data) {
        VERIFY(!global_data.physical_memory_ranges.is_empty());
        for (auto& current_range : global_data.physical_memory_ranges) {
            IterationDecision decision = callback(current_range);
            if (decision != IterationDecision::Continue)
                return decision;
        }
        return IterationDecision::Continue;
    });
}

UNMAP_AFTER_INIT void MemoryManager::register_reserved_ranges()
{
    m_global_data.with([&](auto& global_data) {
        VERIFY(!global_data.physical_memory_ranges.is_empty());
        ContiguousReservedMemoryRange range;
        for (auto& current_range : global_data.physical_memory_ranges) {
            if (current_range.type != PhysicalMemoryRangeType::Reserved) {
                if (range.start.is_null())
                    continue;
                global_data.reserved_memory_ranges.append(ContiguousReservedMemoryRange { range.start, current_range.start.get() - range.start.get() });
                range.start.set((FlatPtr) nullptr);
                continue;
            }
            if (!range.start.is_null()) {
                continue;
            }
            range.start = current_range.start;
        }
        if (global_data.physical_memory_ranges.last().type != PhysicalMemoryRangeType::Reserved)
            return;
        if (range.start.is_null())
            return;
        global_data.reserved_memory_ranges.append(ContiguousReservedMemoryRange { range.start, global_data.physical_memory_ranges.last().start.get() + global_data.physical_memory_ranges.last().length - range.start.get() });
    });
}

bool MemoryManager::is_allowed_to_read_physical_memory_for_userspace(PhysicalAddress start_address, size_t read_length) const
{
    // Note: Guard against overflow in case someone tries to mmap on the edge of
    // the RAM
    if (start_address.offset_addition_would_overflow(read_length))
        return false;
    auto end_address = start_address.offset(read_length);

    return m_global_data.with([&](auto& global_data) {
        for (auto const& current_range : global_data.reserved_memory_ranges) {
            if (current_range.start > start_address)
                continue;
            if (current_range.start.offset(current_range.length) < end_address)
                continue;
            return true;
        }
        return false;
    });
}

UNMAP_AFTER_INIT void MemoryManager::parse_memory_map()
{
    // Register used memory regions that we know of.
    m_global_data.with([&](auto& global_data) {
        global_data.used_memory_ranges.ensure_capacity(4);
#if ARCH(X86_64)
        // NOTE: We don't touch the first 1 MiB of RAM on x86-64 even if it's usable as indicated
        // by a certain memory map. There are 2 reasons for this:
        //
        // The first reason is specified for Linux doing the same thing in
        // https://cateee.net/lkddb/web-lkddb/X86_RESERVE_LOW.html -
        // "By default we reserve the first 64K of physical RAM, as a number of BIOSes are known
        //  to corrupt that memory range during events such as suspend/resume or monitor cable insertion,
        //  so it must not be used by the kernel."
        //
        // Linux also allows configuring this knob in compiletime for this reserved range length, that might
        // also include the EBDA and other potential ranges in the first 1 MiB that could be corrupted by the BIOS:
        // "You can set this to 4 if you are absolutely sure that you trust the BIOS to get all its memory
        //  reservations and usages right. If you know your BIOS have problems beyond the default 64K area,
        //  you can set this to 640 to avoid using the entire low memory range."
        //
        // The second reason is that the first 1 MiB memory range should also include the actual BIOS blob
        // together with possible execution blob code for various option ROMs, which should not be touched
        // by our kernel.
        //
        // **To be completely on the safe side** and never worry about where the EBDA is located, how BIOS might
        // corrupt the low memory range during power state changing, other bad behavior of some BIOS might change
        // a value in the very first 64k bytes of RAM, etc - we should just ignore this range completely.
        global_data.used_memory_ranges.append(UsedMemoryRange { UsedMemoryRangeType::LowMemory, PhysicalAddress(0x00000000), PhysicalAddress(1 * MiB) });
#endif
        global_data.used_memory_ranges.append(UsedMemoryRange { UsedMemoryRangeType::Kernel, PhysicalAddress(virtual_to_low_physical((FlatPtr)start_of_kernel_image)), PhysicalAddress(page_round_up(virtual_to_low_physical((FlatPtr)end_of_kernel_image)).release_value_but_fixme_should_propagate_errors()) });

        if (multiboot_flags & 0x4) {
            auto* bootmods_start = multiboot_copy_boot_modules_array;
            auto* bootmods_end = bootmods_start + multiboot_copy_boot_modules_count;

            for (auto* bootmod = bootmods_start; bootmod < bootmods_end; bootmod++) {
                global_data.used_memory_ranges.append(UsedMemoryRange { UsedMemoryRangeType::BootModule, PhysicalAddress(bootmod->start), PhysicalAddress(bootmod->end) });
            }
        }

        auto* mmap_begin = multiboot_memory_map;
        auto* mmap_end = multiboot_memory_map + multiboot_memory_map_count;

        struct ContiguousPhysicalVirtualRange {
            PhysicalAddress lower;
            PhysicalAddress upper;
        };

        Vector<ContiguousPhysicalVirtualRange> contiguous_physical_ranges;

        for (auto* mmap = mmap_begin; mmap < mmap_end; mmap++) {
            // We have to copy these onto the stack, because we take a reference to these when printing them out,
            // and doing so on a packed struct field is UB.
            auto address = mmap->addr;
            auto length = mmap->len;
            ArmedScopeGuard write_back_guard = [&]() {
                mmap->addr = address;
                mmap->len = length;
            };

            dmesgln("MM: Multiboot mmap: address={:p}, length={}, type={}", address, length, mmap->type);

            auto start_address = PhysicalAddress(address);
            switch (mmap->type) {
            case (MULTIBOOT_MEMORY_AVAILABLE):
                global_data.physical_memory_ranges.append(PhysicalMemoryRange { PhysicalMemoryRangeType::Usable, start_address, length });
                break;
            case (MULTIBOOT_MEMORY_RESERVED):
#if ARCH(X86_64)
                // Workaround for https://gitlab.com/qemu-project/qemu/-/commit/8504f129450b909c88e199ca44facd35d38ba4de
                // That commit added a reserved 12GiB entry for the benefit of virtual firmware.
                // We can safely ignore this block as it isn't actually reserved on any real hardware.
                // From: https://lore.kernel.org/all/20220701161014.3850-1-joao.m.martins@oracle.com/
                // "Always add the HyperTransport range into e820 even when the relocation isn't
                // done *and* there's >= 40 phys bit that would put max phyusical boundary to 1T
                // This should allow virtual firmware to avoid the reserved range at the
                // 1T boundary on VFs with big bars."
                if (address != 0x000000fd00000000 || length != (0x000000ffffffffff - 0x000000fd00000000) + 1)
#endif
                    global_data.physical_memory_ranges.append(PhysicalMemoryRange { PhysicalMemoryRangeType::Reserved, start_address, length });
                break;
            case (MULTIBOOT_MEMORY_ACPI_RECLAIMABLE):
                global_data.physical_memory_ranges.append(PhysicalMemoryRange { PhysicalMemoryRangeType::ACPI_Reclaimable, start_address, length });
                break;
            case (MULTIBOOT_MEMORY_NVS):
                global_data.physical_memory_ranges.append(PhysicalMemoryRange { PhysicalMemoryRangeType::ACPI_NVS, start_address, length });
                break;
            case (MULTIBOOT_MEMORY_BADRAM):
                dmesgln("MM: Warning, detected bad memory range!");
                global_data.physical_memory_ranges.append(PhysicalMemoryRange { PhysicalMemoryRangeType::BadMemory, start_address, length });
                break;
            default:
                dbgln("MM: Unknown range!");
                global_data.physical_memory_ranges.append(PhysicalMemoryRange { PhysicalMemoryRangeType::Unknown, start_address, length });
                break;
            }

            if (mmap->type != MULTIBOOT_MEMORY_AVAILABLE)
                continue;

            // Fix up unaligned memory regions.
            auto diff = (FlatPtr)address % PAGE_SIZE;
            if (diff != 0) {
                dmesgln("MM: Got an unaligned physical_region from the bootloader; correcting {:p} by {} bytes", address, diff);
                diff = PAGE_SIZE - diff;
                address += diff;
                length -= diff;
            }
            if ((length % PAGE_SIZE) != 0) {
                dmesgln("MM: Got an unaligned physical_region from the bootloader; correcting length {} by {} bytes", length, length % PAGE_SIZE);
                length -= length % PAGE_SIZE;
            }
            if (length < PAGE_SIZE) {
                dmesgln("MM: Memory physical_region from bootloader is too small; we want >= {} bytes, but got {} bytes", PAGE_SIZE, length);
                continue;
            }

            for (PhysicalSize page_base = address; page_base <= (address + length); page_base += PAGE_SIZE) {
                auto addr = PhysicalAddress(page_base);

                // Skip used memory ranges.
                bool should_skip = false;
                for (auto& used_range : global_data.used_memory_ranges) {
                    if (addr.get() >= used_range.start.get() && addr.get() <= used_range.end.get()) {
                        should_skip = true;
                        break;
                    }
                }
                if (should_skip)
                    continue;

                if (contiguous_physical_ranges.is_empty() || contiguous_physical_ranges.last().upper.offset(PAGE_SIZE) != addr) {
                    contiguous_physical_ranges.append(ContiguousPhysicalVirtualRange {
                        .lower = addr,
                        .upper = addr,
                    });
                } else {
                    contiguous_physical_ranges.last().upper = addr;
                }
            }
        }

        for (auto& range : contiguous_physical_ranges) {
            global_data.physical_regions.append(PhysicalRegion::try_create(range.lower, range.upper).release_nonnull());
        }

        for (auto& region : global_data.physical_regions)
            global_data.system_memory_info.physical_pages += region->size();

        register_reserved_ranges();
        for (auto& range : global_data.reserved_memory_ranges) {
            dmesgln("MM: Contiguous reserved range from {}, length is {}", range.start, range.length);
        }

        initialize_physical_pages();

        VERIFY(global_data.system_memory_info.physical_pages > 0);

        // We start out with no committed pages
        global_data.system_memory_info.physical_pages_uncommitted = global_data.system_memory_info.physical_pages;

        for (auto& used_range : global_data.used_memory_ranges) {
            dmesgln("MM: {} range @ {} - {} (size {:#x})", UserMemoryRangeTypeNames[to_underlying(used_range.type)], used_range.start, used_range.end.offset(-1), used_range.end.as_ptr() - used_range.start.as_ptr());
        }

        for (auto& region : global_data.physical_regions) {
            dmesgln("MM: User physical region: {} - {} (size {:#x})", region->lower(), region->upper().offset(-1), PAGE_SIZE * region->size());
            region->initialize_zones();
        }
    });
}

UNMAP_AFTER_INIT void MemoryManager::initialize_physical_pages()
{
    m_global_data.with([&](auto& global_data) {
        // We assume that the physical page range is contiguous and doesn't contain huge gaps!
        PhysicalAddress highest_physical_address;
        for (auto& range : global_data.used_memory_ranges) {
            if (range.end.get() > highest_physical_address.get())
                highest_physical_address = range.end;
        }
        for (auto& region : global_data.physical_memory_ranges) {
            auto range_end = PhysicalAddress(region.start).offset(region.length);
            if (range_end.get() > highest_physical_address.get())
                highest_physical_address = range_end;
        }

        // Calculate how many total physical pages the array will have
        m_physical_page_entries_count = PhysicalAddress::physical_page_index(highest_physical_address.get()) + 1;
        VERIFY(m_physical_page_entries_count != 0);
        VERIFY(!Checked<decltype(m_physical_page_entries_count)>::multiplication_would_overflow(m_physical_page_entries_count, sizeof(PhysicalPageEntry)));

        // Calculate how many bytes the array will consume
        auto physical_page_array_size = m_physical_page_entries_count * sizeof(PhysicalPageEntry);
        auto physical_page_array_pages = page_round_up(physical_page_array_size).release_value_but_fixme_should_propagate_errors() / PAGE_SIZE;
        VERIFY(physical_page_array_pages * PAGE_SIZE >= physical_page_array_size);

        // Calculate how many page tables we will need to be able to map them all
        auto needed_page_table_count = (physical_page_array_pages + 512 - 1) / 512;

        auto physical_page_array_pages_and_page_tables_count = physical_page_array_pages + needed_page_table_count;

        // Now that we know how much memory we need for a contiguous array of PhysicalPage instances, find a memory region that can fit it
        PhysicalRegion* found_region { nullptr };
        Optional<size_t> found_region_index;
        for (size_t i = 0; i < global_data.physical_regions.size(); ++i) {
            auto& region = global_data.physical_regions[i];
            if (region->size() >= physical_page_array_pages_and_page_tables_count) {
                found_region = region;
                found_region_index = i;
                break;
            }
        }

        if (!found_region) {
            dmesgln("MM: Need {} bytes for physical page management, but no memory region is large enough!", physical_page_array_pages_and_page_tables_count);
            VERIFY_NOT_REACHED();
        }

        VERIFY(global_data.system_memory_info.physical_pages >= physical_page_array_pages_and_page_tables_count);
        global_data.system_memory_info.physical_pages -= physical_page_array_pages_and_page_tables_count;

        if (found_region->size() == physical_page_array_pages_and_page_tables_count) {
            // We're stealing the entire region
            global_data.physical_pages_region = global_data.physical_regions.take(*found_region_index);
        } else {
            global_data.physical_pages_region = found_region->try_take_pages_from_beginning(physical_page_array_pages_and_page_tables_count);
        }
        global_data.used_memory_ranges.append({ UsedMemoryRangeType::PhysicalPages, global_data.physical_pages_region->lower(), global_data.physical_pages_region->upper() });

        // Create the bare page directory. This is not a fully constructed page directory and merely contains the allocators!
        m_kernel_page_directory = PageDirectory::must_create_kernel_page_directory();

        {
            // Carve out the whole page directory covering the kernel image to make MemoryManager::initialize_physical_pages() happy
            FlatPtr start_of_range = ((FlatPtr)start_of_kernel_image & ~(FlatPtr)0x1fffff);
            FlatPtr end_of_range = ((FlatPtr)end_of_kernel_image & ~(FlatPtr)0x1fffff) + 0x200000;
            MUST(global_data.region_tree.place_specifically(*MUST(Region::create_unbacked()).leak_ptr(), VirtualRange { VirtualAddress(start_of_range), end_of_range - start_of_range }));
        }

        // Allocate a virtual address range for our array
        // This looks awkward, but it basically creates a dummy region to occupy the address range permanently.
        auto& region = *MUST(Region::create_unbacked()).leak_ptr();
        MUST(global_data.region_tree.place_anywhere(region, RandomizeVirtualAddress::No, physical_page_array_pages * PAGE_SIZE));
        auto range = region.range();

        // Now that we have our special m_physical_pages_region region with enough pages to hold the entire array
        // try to map the entire region into kernel space so we always have it
        // We can't use ensure_pte here because it would try to allocate a PhysicalPage and we don't have the array
        // mapped yet so we can't create them

        // Create page tables at the beginning of m_physical_pages_region, followed by the PhysicalPageEntry array
        auto page_tables_base = global_data.physical_pages_region->lower();
        auto physical_page_array_base = page_tables_base.offset(needed_page_table_count * PAGE_SIZE);
        auto physical_page_array_current_page = physical_page_array_base.get();
        auto virtual_page_array_base = range.base().get();
        auto virtual_page_array_current_page = virtual_page_array_base;
        for (size_t pt_index = 0; pt_index < needed_page_table_count; pt_index++) {
            auto virtual_page_base_for_this_pt = virtual_page_array_current_page;
            auto pt_paddr = page_tables_base.offset(pt_index * PAGE_SIZE);
            auto* pt = reinterpret_cast<PageTableEntry*>(quickmap_page(pt_paddr));
            __builtin_memset(pt, 0, PAGE_SIZE);
            for (size_t pte_index = 0; pte_index < PAGE_SIZE / sizeof(PageTableEntry); pte_index++) {
                auto& pte = pt[pte_index];
                pte.set_physical_page_base(physical_page_array_current_page);
                pte.set_user_allowed(false);
                pte.set_writable(true);
                if (Processor::current().has_nx())
                    pte.set_execute_disabled(false);
                pte.set_global(true);
                pte.set_present(true);

                physical_page_array_current_page += PAGE_SIZE;
                virtual_page_array_current_page += PAGE_SIZE;
            }
            unquickmap_page();

            // Hook the page table into the kernel page directory
            u32 page_directory_index = (virtual_page_base_for_this_pt >> 21) & 0x1ff;
            auto* pd = reinterpret_cast<PageDirectoryEntry*>(quickmap_page(boot_pd_kernel));
            PageDirectoryEntry& pde = pd[page_directory_index];

            VERIFY(!pde.is_present()); // Nothing should be using this PD yet

            // We can't use ensure_pte quite yet!
            pde.set_page_table_base(pt_paddr.get());
            pde.set_user_allowed(false);
            pde.set_present(true);
            pde.set_writable(true);
            pde.set_global(true);

            unquickmap_page();

            flush_tlb_local(VirtualAddress(virtual_page_base_for_this_pt));
        }

        // We now have the entire PhysicalPageEntry array mapped!
        m_physical_page_entries = (PhysicalPageEntry*)range.base().get();
        for (size_t i = 0; i < m_physical_page_entries_count; i++)
            new (&m_physical_page_entries[i]) PageTableEntry();

        // Now we should be able to allocate PhysicalPage instances,
        // so finish setting up the kernel page directory
        m_kernel_page_directory->allocate_kernel_directory();

        // Now create legit PhysicalPage objects for the page tables we created.
        virtual_page_array_current_page = virtual_page_array_base;
        for (size_t pt_index = 0; pt_index < needed_page_table_count; pt_index++) {
            VERIFY(virtual_page_array_current_page <= range.end().get());
            auto pt_paddr = page_tables_base.offset(pt_index * PAGE_SIZE);
            auto physical_page_index = PhysicalAddress::physical_page_index(pt_paddr.get());
            auto& physical_page_entry = m_physical_page_entries[physical_page_index];
            auto physical_page = adopt_lock_ref(*new (&physical_page_entry.allocated.physical_page) PhysicalPage(MayReturnToFreeList::No));

            // NOTE: This leaked ref is matched by the unref in MemoryManager::release_pte()
            (void)physical_page.leak_ref();

            virtual_page_array_current_page += (PAGE_SIZE / sizeof(PageTableEntry)) * PAGE_SIZE;
        }

        dmesgln("MM: Physical page entries: {}", range);
    });
}

PhysicalPageEntry& MemoryManager::get_physical_page_entry(PhysicalAddress physical_address)
{
    auto physical_page_entry_index = PhysicalAddress::physical_page_index(physical_address.get());
    VERIFY(physical_page_entry_index < m_physical_page_entries_count);
    return m_physical_page_entries[physical_page_entry_index];
}

PhysicalAddress MemoryManager::get_physical_address(PhysicalPage const& physical_page)
{
    PhysicalPageEntry const& physical_page_entry = *reinterpret_cast<PhysicalPageEntry const*>((u8 const*)&physical_page - __builtin_offsetof(PhysicalPageEntry, allocated.physical_page));
    size_t physical_page_entry_index = &physical_page_entry - m_physical_page_entries;
    VERIFY(physical_page_entry_index < m_physical_page_entries_count);
    return PhysicalAddress((PhysicalPtr)physical_page_entry_index * PAGE_SIZE);
}

PageTableEntry* MemoryManager::pte(PageDirectory& page_directory, VirtualAddress vaddr)
{
    VERIFY_INTERRUPTS_DISABLED();
    VERIFY(page_directory.get_lock().is_locked_by_current_processor());
    u32 page_directory_table_index = (vaddr.get() >> 30) & 0x1ff;
    u32 page_directory_index = (vaddr.get() >> 21) & 0x1ff;
    u32 page_table_index = (vaddr.get() >> 12) & 0x1ff;

    auto* pd = quickmap_pd(const_cast<PageDirectory&>(page_directory), page_directory_table_index);
    PageDirectoryEntry const& pde = pd[page_directory_index];
    if (!pde.is_present())
        return nullptr;

    return &quickmap_pt(PhysicalAddress((FlatPtr)pde.page_table_base()))[page_table_index];
}

PageTableEntry* MemoryManager::ensure_pte(PageDirectory& page_directory, VirtualAddress vaddr)
{
    VERIFY_INTERRUPTS_DISABLED();
    VERIFY(page_directory.get_lock().is_locked_by_current_processor());
    u32 page_directory_table_index = (vaddr.get() >> 30) & 0x1ff;
    u32 page_directory_index = (vaddr.get() >> 21) & 0x1ff;
    u32 page_table_index = (vaddr.get() >> 12) & 0x1ff;

    auto* pd = quickmap_pd(page_directory, page_directory_table_index);
    auto& pde = pd[page_directory_index];
    if (pde.is_present())
        return &quickmap_pt(PhysicalAddress(pde.page_table_base()))[page_table_index];

    bool did_purge = false;
    auto page_table_or_error = allocate_physical_page(ShouldZeroFill::Yes, &did_purge);
    if (page_table_or_error.is_error()) {
        dbgln("MM: Unable to allocate page table to map {}", vaddr);
        return nullptr;
    }
    auto page_table = page_table_or_error.release_value();
    if (did_purge) {
        // If any memory had to be purged, ensure_pte may have been called as part
        // of the purging process. So we need to re-map the pd in this case to ensure
        // we're writing to the correct underlying physical page
        pd = quickmap_pd(page_directory, page_directory_table_index);
        VERIFY(&pde == &pd[page_directory_index]); // Sanity check

        VERIFY(!pde.is_present()); // Should have not changed
    }
    pde.set_page_table_base(page_table->paddr().get());
    pde.set_user_allowed(true);
    pde.set_present(true);
    pde.set_writable(true);
    pde.set_global(&page_directory == m_kernel_page_directory.ptr());

    // NOTE: This leaked ref is matched by the unref in MemoryManager::release_pte()
    (void)page_table.leak_ref();

    return &quickmap_pt(PhysicalAddress(pde.page_table_base()))[page_table_index];
}

void MemoryManager::release_pte(PageDirectory& page_directory, VirtualAddress vaddr, IsLastPTERelease is_last_pte_release)
{
    VERIFY_INTERRUPTS_DISABLED();
    VERIFY(page_directory.get_lock().is_locked_by_current_processor());
    u32 page_directory_table_index = (vaddr.get() >> 30) & 0x1ff;
    u32 page_directory_index = (vaddr.get() >> 21) & 0x1ff;
    u32 page_table_index = (vaddr.get() >> 12) & 0x1ff;

    auto* pd = quickmap_pd(page_directory, page_directory_table_index);
    PageDirectoryEntry& pde = pd[page_directory_index];
    if (pde.is_present()) {
        auto* page_table = quickmap_pt(PhysicalAddress((FlatPtr)pde.page_table_base()));
        auto& pte = page_table[page_table_index];
        pte.clear();

        if (is_last_pte_release == IsLastPTERelease::Yes || page_table_index == 0x1ff) {
            // If this is the last PTE in a region or the last PTE in a page table then
            // check if we can also release the page table
            bool all_clear = true;
            for (u32 i = 0; i <= 0x1ff; i++) {
                if (!page_table[i].is_null()) {
                    all_clear = false;
                    break;
                }
            }
            if (all_clear) {
                get_physical_page_entry(PhysicalAddress { pde.page_table_base() }).allocated.physical_page.unref();
                pde.clear();
            }
        }
    }
}

UNMAP_AFTER_INIT void MemoryManager::initialize(u32 cpu)
{
    dmesgln("Initialize MMU");
    ProcessorSpecific<MemoryManagerData>::initialize();

    if (cpu == 0) {
        new MemoryManager;
        kmalloc_enable_expand();
    }
}

Region* MemoryManager::find_user_region_from_vaddr(AddressSpace& space, VirtualAddress vaddr)
{
    return space.find_region_containing({ vaddr, 1 });
}

void MemoryManager::validate_syscall_preconditions(Process& process, RegisterState const& regs)
{
    bool should_crash = false;
    char const* crash_description = nullptr;
    int crash_signal = 0;

    auto unlock_and_handle_crash = [&](char const* description, int signal) {
        should_crash = true;
        crash_description = description;
        crash_signal = signal;
    };

    process.address_space().with([&](auto& space) -> void {
        VirtualAddress userspace_sp = VirtualAddress { regs.userspace_sp() };
        if (!MM.validate_user_stack(*space, userspace_sp)) {
            dbgln("Invalid stack pointer: {}", userspace_sp);
            return unlock_and_handle_crash("Bad stack on syscall entry", SIGSEGV);
        }

        VirtualAddress ip = VirtualAddress { regs.ip() };
        auto* calling_region = MM.find_user_region_from_vaddr(*space, ip);
        if (!calling_region) {
            dbgln("Syscall from {:p} which has no associated region", ip);
            return unlock_and_handle_crash("Syscall from unknown region", SIGSEGV);
        }

        if (calling_region->is_writable()) {
            dbgln("Syscall from writable memory at {:p}", ip);
            return unlock_and_handle_crash("Syscall from writable memory", SIGSEGV);
        }

        if (space->enforces_syscall_regions() && !calling_region->is_syscall_region()) {
            dbgln("Syscall from non-syscall region");
            return unlock_and_handle_crash("Syscall from non-syscall region", SIGSEGV);
        }
    });

    if (should_crash) {
        handle_crash(regs, crash_description, crash_signal);
    }
}

PageFaultResponse MemoryManager::handle_page_fault(PageFault const& fault)
{
    auto faulted_in_range = [&fault](auto const* start, auto const* end) {
        return fault.vaddr() >= VirtualAddress { start } && fault.vaddr() < VirtualAddress { end };
    };

    if (faulted_in_range(&start_of_ro_after_init, &end_of_ro_after_init)) {
        dbgln("Attempt to write into READONLY_AFTER_INIT section");
        return PageFaultResponse::ShouldCrash;
    }

    if (faulted_in_range(&start_of_unmap_after_init, &end_of_unmap_after_init)) {
        auto const* kernel_symbol = symbolicate_kernel_address(fault.vaddr().get());
        dbgln("Attempt to access UNMAP_AFTER_INIT section ({}: {})", fault.vaddr(), kernel_symbol ? kernel_symbol->name : "(Unknown)");
        return PageFaultResponse::ShouldCrash;
    }

    if (faulted_in_range(&start_of_kernel_ksyms, &end_of_kernel_ksyms)) {
        dbgln("Attempt to access KSYMS section");
        return PageFaultResponse::ShouldCrash;
    }

    if (Processor::current_in_irq()) {
        dbgln("CPU[{}] BUG! Page fault while handling IRQ! code={}, vaddr={}, irq level: {}",
            Processor::current_id(), fault.code(), fault.vaddr(), Processor::current_in_irq());
        dump_kernel_regions();
        return PageFaultResponse::ShouldCrash;
    }
    dbgln_if(PAGE_FAULT_DEBUG, "MM: CPU[{}] handle_page_fault({:#04x}) at {}", Processor::current_id(), fault.code(), fault.vaddr());

    // The faulting region may be unmapped concurrently to handling this page fault, and since
    // regions are singly-owned it would usually result in the region being immediately
    // de-allocated. To ensure the region is not de-allocated while we're still handling the
    // fault we increase a page fault counter on the region, and the region will refrain from
    // de-allocating itself until the counter reaches zero. (Since unmapping the region also
    // includes removing it from the region tree while holding the address space spinlock, and
    // because we increment the counter while still holding the spinlock it is guaranteed that
    // we always increment the counter before it gets a chance to be deleted)
    Region* region = nullptr;
    if (is_user_address(fault.vaddr())) {
        auto page_directory = PageDirectory::find_current();
        if (!page_directory)
            return PageFaultResponse::ShouldCrash;
        auto* process = page_directory->process();
        VERIFY(process);
        region = process->address_space().with([&](auto& space) -> Region* {
            auto* region = find_user_region_from_vaddr(*space, fault.vaddr());
            if (!region)
                return nullptr;
            region->start_handling_page_fault({});
            return region;
        });
    } else {
        region = MM.m_global_data.with([&](auto& global_data) -> Region* {
            auto* region = global_data.region_tree.find_region_containing(fault.vaddr());
            if (!region)
                return nullptr;
            region->start_handling_page_fault({});
            return region;
        });
    }
    if (!region)
        return PageFaultResponse::ShouldCrash;

    auto response = region->handle_fault(fault);
    region->finish_handling_page_fault({});
    return response;
}

ErrorOr<NonnullOwnPtr<Region>> MemoryManager::allocate_contiguous_kernel_region(size_t size, StringView name, Region::Access access, Region::Cacheable cacheable)
{
    VERIFY(!(size % PAGE_SIZE));
    OwnPtr<KString> name_kstring;
    if (!name.is_null())
        name_kstring = TRY(KString::try_create(name));
    auto vmobject = TRY(AnonymousVMObject::try_create_physically_contiguous_with_size(size));
    auto region = TRY(Region::create_unplaced(move(vmobject), 0, move(name_kstring), access, cacheable));
    TRY(m_global_data.with([&](auto& global_data) { return global_data.region_tree.place_anywhere(*region, RandomizeVirtualAddress::No, size); }));
    TRY(region->map(kernel_page_directory()));
    return region;
}

ErrorOr<NonnullOwnPtr<Memory::Region>> MemoryManager::allocate_dma_buffer_page(StringView name, Memory::Region::Access access, RefPtr<Memory::PhysicalPage>& dma_buffer_page)
{
    dma_buffer_page = TRY(allocate_physical_page());
    // Do not enable Cache for this region as physical memory transfers are performed (Most architectures have this behavior by default)
    return allocate_kernel_region(dma_buffer_page->paddr(), PAGE_SIZE, name, access, Region::Cacheable::No);
}

ErrorOr<NonnullOwnPtr<Memory::Region>> MemoryManager::allocate_dma_buffer_page(StringView name, Memory::Region::Access access)
{
    RefPtr<Memory::PhysicalPage> dma_buffer_page;

    return allocate_dma_buffer_page(name, access, dma_buffer_page);
}

ErrorOr<NonnullOwnPtr<Memory::Region>> MemoryManager::allocate_dma_buffer_pages(size_t size, StringView name, Memory::Region::Access access, Vector<NonnullRefPtr<Memory::PhysicalPage>>& dma_buffer_pages)
{
    VERIFY(!(size % PAGE_SIZE));
    dma_buffer_pages = TRY(allocate_contiguous_physical_pages(size));
    // Do not enable Cache for this region as physical memory transfers are performed (Most architectures have this behavior by default)
    return allocate_kernel_region(dma_buffer_pages.first()->paddr(), size, name, access, Region::Cacheable::No);
}

ErrorOr<NonnullOwnPtr<Memory::Region>> MemoryManager::allocate_dma_buffer_pages(size_t size, StringView name, Memory::Region::Access access)
{
    VERIFY(!(size % PAGE_SIZE));
    Vector<NonnullRefPtr<Memory::PhysicalPage>> dma_buffer_pages;

    return allocate_dma_buffer_pages(size, name, access, dma_buffer_pages);
}

ErrorOr<NonnullOwnPtr<Region>> MemoryManager::allocate_kernel_region(size_t size, StringView name, Region::Access access, AllocationStrategy strategy, Region::Cacheable cacheable)
{
    VERIFY(!(size % PAGE_SIZE));
    OwnPtr<KString> name_kstring;
    if (!name.is_null())
        name_kstring = TRY(KString::try_create(name));
    auto vmobject = TRY(AnonymousVMObject::try_create_with_size(size, strategy));
    auto region = TRY(Region::create_unplaced(move(vmobject), 0, move(name_kstring), access, cacheable));
    TRY(m_global_data.with([&](auto& global_data) { return global_data.region_tree.place_anywhere(*region, RandomizeVirtualAddress::No, size); }));
    TRY(region->map(kernel_page_directory()));
    return region;
}

ErrorOr<NonnullOwnPtr<Region>> MemoryManager::allocate_kernel_region(PhysicalAddress paddr, size_t size, StringView name, Region::Access access, Region::Cacheable cacheable)
{
    VERIFY(!(size % PAGE_SIZE));
    auto vmobject = TRY(AnonymousVMObject::try_create_for_physical_range(paddr, size));
    OwnPtr<KString> name_kstring;
    if (!name.is_null())
        name_kstring = TRY(KString::try_create(name));
    auto region = TRY(Region::create_unplaced(move(vmobject), 0, move(name_kstring), access, cacheable));
    TRY(m_global_data.with([&](auto& global_data) { return global_data.region_tree.place_anywhere(*region, RandomizeVirtualAddress::No, size, PAGE_SIZE); }));
    TRY(region->map(kernel_page_directory()));
    return region;
}

ErrorOr<NonnullOwnPtr<Region>> MemoryManager::allocate_kernel_region_with_vmobject(VMObject& vmobject, size_t size, StringView name, Region::Access access, Region::Cacheable cacheable)
{
    VERIFY(!(size % PAGE_SIZE));

    OwnPtr<KString> name_kstring;
    if (!name.is_null())
        name_kstring = TRY(KString::try_create(name));

    auto region = TRY(Region::create_unplaced(vmobject, 0, move(name_kstring), access, cacheable));
    TRY(m_global_data.with([&](auto& global_data) { return global_data.region_tree.place_anywhere(*region, RandomizeVirtualAddress::No, size); }));
    TRY(region->map(kernel_page_directory()));
    return region;
}

ErrorOr<CommittedPhysicalPageSet> MemoryManager::commit_physical_pages(size_t page_count)
{
    VERIFY(page_count > 0);
    auto result = m_global_data.with([&](auto& global_data) -> ErrorOr<CommittedPhysicalPageSet> {
        if (global_data.system_memory_info.physical_pages_uncommitted < page_count) {
            dbgln("MM: Unable to commit {} pages, have only {}", page_count, global_data.system_memory_info.physical_pages_uncommitted);
            return ENOMEM;
        }

        global_data.system_memory_info.physical_pages_uncommitted -= page_count;
        global_data.system_memory_info.physical_pages_committed += page_count;
        return CommittedPhysicalPageSet { {}, page_count };
    });
    if (result.is_error()) {
        Process::for_each_ignoring_jails([&](Process const& process) {
            size_t amount_resident = 0;
            size_t amount_shared = 0;
            size_t amount_virtual = 0;
            process.address_space().with([&](auto& space) {
                amount_resident = space->amount_resident();
                amount_shared = space->amount_shared();
                amount_virtual = space->amount_virtual();
            });
            process.name().with([&](auto& process_name) {
                dbgln("{}({}) resident:{}, shared:{}, virtual:{}",
                    process_name->view(),
                    process.pid(),
                    amount_resident / PAGE_SIZE,
                    amount_shared / PAGE_SIZE,
                    amount_virtual / PAGE_SIZE);
            });
            return IterationDecision::Continue;
        });
    }
    return result;
}

void MemoryManager::uncommit_physical_pages(Badge<CommittedPhysicalPageSet>, size_t page_count)
{
    VERIFY(page_count > 0);

    m_global_data.with([&](auto& global_data) {
        VERIFY(global_data.system_memory_info.physical_pages_committed >= page_count);

        global_data.system_memory_info.physical_pages_uncommitted += page_count;
        global_data.system_memory_info.physical_pages_committed -= page_count;
    });
}

void MemoryManager::deallocate_physical_page(PhysicalAddress paddr)
{
    return m_global_data.with([&](auto& global_data) {
        // Are we returning a user page?
        for (auto& region : global_data.physical_regions) {
            if (!region->contains(paddr))
                continue;

            region->return_page(paddr);
            --global_data.system_memory_info.physical_pages_used;

            // Always return pages to the uncommitted pool. Pages that were
            // committed and allocated are only freed upon request. Once
            // returned there is no guarantee being able to get them back.
            ++global_data.system_memory_info.physical_pages_uncommitted;
            return;
        }
        PANIC("MM: deallocate_physical_page couldn't figure out region for page @ {}", paddr);
    });
}

RefPtr<PhysicalPage> MemoryManager::find_free_physical_page(bool committed)
{
    RefPtr<PhysicalPage> page;
    m_global_data.with([&](auto& global_data) {
        if (committed) {
            // Draw from the committed pages pool. We should always have these pages available
            VERIFY(global_data.system_memory_info.physical_pages_committed > 0);
            global_data.system_memory_info.physical_pages_committed--;
        } else {
            // We need to make sure we don't touch pages that we have committed to
            if (global_data.system_memory_info.physical_pages_uncommitted == 0)
                return;
            global_data.system_memory_info.physical_pages_uncommitted--;
        }
        for (auto& region : global_data.physical_regions) {
            page = region->take_free_page();
            if (!page.is_null()) {
                ++global_data.system_memory_info.physical_pages_used;
                break;
            }
        }
    });

    if (page.is_null())
        dbgln("MM: couldn't find free physical page. Continuing...");

    return page;
}

NonnullRefPtr<PhysicalPage> MemoryManager::allocate_committed_physical_page(Badge<CommittedPhysicalPageSet>, ShouldZeroFill should_zero_fill)
{
    auto page = find_free_physical_page(true);
    VERIFY(page);
    if (should_zero_fill == ShouldZeroFill::Yes) {
        InterruptDisabler disabler;
        auto* ptr = quickmap_page(*page);
        memset(ptr, 0, PAGE_SIZE);
        unquickmap_page();
    }
    return page.release_nonnull();
}

ErrorOr<NonnullRefPtr<PhysicalPage>> MemoryManager::allocate_physical_page(ShouldZeroFill should_zero_fill, bool* did_purge)
{
    return m_global_data.with([&](auto&) -> ErrorOr<NonnullRefPtr<PhysicalPage>> {
        auto page = find_free_physical_page(false);
        bool purged_pages = false;

        if (!page) {
            // We didn't have a single free physical page. Let's try to free something up!
            // First, we look for a purgeable VMObject in the volatile state.
            for_each_vmobject([&](auto& vmobject) {
                if (!vmobject.is_anonymous())
                    return IterationDecision::Continue;
                auto& anonymous_vmobject = static_cast<AnonymousVMObject&>(vmobject);
                if (!anonymous_vmobject.is_purgeable() || !anonymous_vmobject.is_volatile())
                    return IterationDecision::Continue;
                if (auto purged_page_count = anonymous_vmobject.purge()) {
                    dbgln("MM: Purge saved the day! Purged {} pages from AnonymousVMObject", purged_page_count);
                    page = find_free_physical_page(false);
                    purged_pages = true;
                    VERIFY(page);
                    return IterationDecision::Break;
                }
                return IterationDecision::Continue;
            });
        }
        if (!page) {
            // Second, we look for a file-backed VMObject with clean pages.
            for_each_vmobject([&](auto& vmobject) {
                if (!vmobject.is_inode())
                    return IterationDecision::Continue;
                auto& inode_vmobject = static_cast<InodeVMObject&>(vmobject);
                if (auto released_page_count = inode_vmobject.try_release_clean_pages(1)) {
                    dbgln("MM: Clean inode release saved the day! Released {} pages from InodeVMObject", released_page_count);
                    page = find_free_physical_page(false);
                    VERIFY(page);
                    return IterationDecision::Break;
                }
                return IterationDecision::Continue;
            });
        }
        if (!page) {
            dmesgln("MM: no physical pages available");
            return ENOMEM;
        }

        if (should_zero_fill == ShouldZeroFill::Yes) {
            auto* ptr = quickmap_page(*page);
            memset(ptr, 0, PAGE_SIZE);
            unquickmap_page();
        }

        if (did_purge)
            *did_purge = purged_pages;
        return page.release_nonnull();
    });
}

ErrorOr<Vector<NonnullRefPtr<PhysicalPage>>> MemoryManager::allocate_contiguous_physical_pages(size_t size)
{
    VERIFY(!(size % PAGE_SIZE));
    size_t page_count = ceil_div(size, static_cast<size_t>(PAGE_SIZE));

    auto physical_pages = TRY(m_global_data.with([&](auto& global_data) -> ErrorOr<Vector<NonnullRefPtr<PhysicalPage>>> {
        // We need to make sure we don't touch pages that we have committed to
        if (global_data.system_memory_info.physical_pages_uncommitted < page_count)
            return ENOMEM;

        for (auto& physical_region : global_data.physical_regions) {
            auto physical_pages = physical_region->take_contiguous_free_pages(page_count);
            if (!physical_pages.is_empty()) {
                global_data.system_memory_info.physical_pages_uncommitted -= page_count;
                global_data.system_memory_info.physical_pages_used += page_count;
                return physical_pages;
            }
        }
        dmesgln("MM: no contiguous physical pages available");
        return ENOMEM;
    }));

    {
        auto cleanup_region = TRY(MM.allocate_kernel_region(physical_pages[0]->paddr(), PAGE_SIZE * page_count, {}, Region::Access::Read | Region::Access::Write));
        memset(cleanup_region->vaddr().as_ptr(), 0, PAGE_SIZE * page_count);
    }
    return physical_pages;
}

void MemoryManager::enter_process_address_space(Process& process)
{
    process.address_space().with([](auto& space) {
        enter_address_space(*space);
    });
}

void MemoryManager::enter_address_space(AddressSpace& space)
{
    auto* current_thread = Thread::current();
    VERIFY(current_thread != nullptr);
    activate_page_directory(space.page_directory(), current_thread);
}

void MemoryManager::flush_tlb_local(VirtualAddress vaddr, size_t page_count)
{
    Processor::flush_tlb_local(vaddr, page_count);
}

void MemoryManager::flush_tlb(PageDirectory const* page_directory, VirtualAddress vaddr, size_t page_count)
{
    Processor::flush_tlb(page_directory, vaddr, page_count);
}

PageDirectoryEntry* MemoryManager::quickmap_pd(PageDirectory& directory, size_t pdpt_index)
{
    VERIFY_INTERRUPTS_DISABLED();

    VirtualAddress vaddr(KERNEL_QUICKMAP_PD_PER_CPU_BASE + Processor::current_id() * PAGE_SIZE);
    size_t pte_index = (vaddr.get() - KERNEL_PT1024_BASE) / PAGE_SIZE;

    auto& pte = boot_pd_kernel_pt1023[pte_index];
    auto pd_paddr = directory.m_directory_pages[pdpt_index]->paddr();
    if (pte.physical_page_base() != pd_paddr.get()) {
        pte.set_physical_page_base(pd_paddr.get());
        pte.set_present(true);
        pte.set_writable(true);
        pte.set_user_allowed(false);
        flush_tlb_local(vaddr);
    }
    return (PageDirectoryEntry*)vaddr.get();
}

PageTableEntry* MemoryManager::quickmap_pt(PhysicalAddress pt_paddr)
{
    VERIFY_INTERRUPTS_DISABLED();

    VirtualAddress vaddr(KERNEL_QUICKMAP_PT_PER_CPU_BASE + Processor::current_id() * PAGE_SIZE);
    size_t pte_index = (vaddr.get() - KERNEL_PT1024_BASE) / PAGE_SIZE;

    auto& pte = ((PageTableEntry*)boot_pd_kernel_pt1023)[pte_index];
    if (pte.physical_page_base() != pt_paddr.get()) {
        pte.set_physical_page_base(pt_paddr.get());
        pte.set_present(true);
        pte.set_writable(true);
        pte.set_user_allowed(false);
        flush_tlb_local(vaddr);
    }
    return (PageTableEntry*)vaddr.get();
}

u8* MemoryManager::quickmap_page(PhysicalAddress const& physical_address)
{
    VERIFY_INTERRUPTS_DISABLED();
    auto& mm_data = get_data();
    mm_data.m_quickmap_previous_interrupts_state = mm_data.m_quickmap_in_use.lock();

    VirtualAddress vaddr(KERNEL_QUICKMAP_PER_CPU_BASE + Processor::current_id() * PAGE_SIZE);
    u32 pte_idx = (vaddr.get() - KERNEL_PT1024_BASE) / PAGE_SIZE;

    auto& pte = ((PageTableEntry*)boot_pd_kernel_pt1023)[pte_idx];
    if (pte.physical_page_base() != physical_address.get()) {
        pte.set_physical_page_base(physical_address.get());
        pte.set_present(true);
        pte.set_writable(true);
        pte.set_user_allowed(false);
        flush_tlb_local(vaddr);
    }
    return vaddr.as_ptr();
}

void MemoryManager::unquickmap_page()
{
    VERIFY_INTERRUPTS_DISABLED();
    auto& mm_data = get_data();
    VERIFY(mm_data.m_quickmap_in_use.is_locked());
    VirtualAddress vaddr(KERNEL_QUICKMAP_PER_CPU_BASE + Processor::current_id() * PAGE_SIZE);
    u32 pte_idx = (vaddr.get() - KERNEL_PT1024_BASE) / PAGE_SIZE;
    auto& pte = ((PageTableEntry*)boot_pd_kernel_pt1023)[pte_idx];
    pte.clear();
    flush_tlb_local(vaddr);
    mm_data.m_quickmap_in_use.unlock(mm_data.m_quickmap_previous_interrupts_state);
}

bool MemoryManager::validate_user_stack(AddressSpace& space, VirtualAddress vaddr) const
{
    if (!is_user_address(vaddr))
        return false;

    auto* region = find_user_region_from_vaddr(space, vaddr);
    return region && region->is_user() && region->is_stack();
}

void MemoryManager::unregister_kernel_region(Region& region)
{
    VERIFY(region.is_kernel());
    m_global_data.with([&](auto& global_data) { global_data.region_tree.remove(region); });
}

void MemoryManager::dump_kernel_regions()
{
    dbgln("Kernel regions:");
    char const* addr_padding = "        ";
    dbgln("BEGIN{}         END{}        SIZE{}       ACCESS NAME",
        addr_padding, addr_padding, addr_padding);
    m_global_data.with([&](auto& global_data) {
        for (auto& region : global_data.region_tree.regions()) {
            dbgln("{:p} -- {:p} {:p} {:c}{:c}{:c}{:c}{:c}{:c} {}",
                region.vaddr().get(),
                region.vaddr().offset(region.size() - 1).get(),
                region.size(),
                region.is_readable() ? 'R' : ' ',
                region.is_writable() ? 'W' : ' ',
                region.is_executable() ? 'X' : ' ',
                region.is_shared() ? 'S' : ' ',
                region.is_stack() ? 'T' : ' ',
                region.is_syscall_region() ? 'C' : ' ',
                region.name());
        }
    });
}

void MemoryManager::set_page_writable_direct(VirtualAddress vaddr, bool writable)
{
    SpinlockLocker page_lock(kernel_page_directory().get_lock());
    auto* pte = ensure_pte(kernel_page_directory(), vaddr);
    VERIFY(pte);
    if (pte->is_writable() == writable)
        return;
    pte->set_writable(writable);
    flush_tlb(&kernel_page_directory(), vaddr);
}

CommittedPhysicalPageSet::~CommittedPhysicalPageSet()
{
    if (m_page_count)
        MM.uncommit_physical_pages({}, m_page_count);
}

NonnullRefPtr<PhysicalPage> CommittedPhysicalPageSet::take_one()
{
    VERIFY(m_page_count > 0);
    --m_page_count;
    return MM.allocate_committed_physical_page({}, MemoryManager::ShouldZeroFill::Yes);
}

void CommittedPhysicalPageSet::uncommit_one()
{
    VERIFY(m_page_count > 0);
    --m_page_count;
    MM.uncommit_physical_pages({}, 1);
}

void MemoryManager::copy_physical_page(PhysicalPage& physical_page, u8 page_buffer[PAGE_SIZE])
{
    auto* quickmapped_page = quickmap_page(physical_page);
    memcpy(page_buffer, quickmapped_page, PAGE_SIZE);
    unquickmap_page();
}

ErrorOr<NonnullOwnPtr<Memory::Region>> MemoryManager::create_identity_mapped_region(PhysicalAddress address, size_t size)
{
    auto vmobject = TRY(Memory::AnonymousVMObject::try_create_for_physical_range(address, size));
    auto region = TRY(Memory::Region::create_unplaced(move(vmobject), 0, {}, Memory::Region::Access::ReadWriteExecute));
    Memory::VirtualRange range { VirtualAddress { (FlatPtr)address.get() }, size };
    region->m_range = range;
    TRY(region->map(MM.kernel_page_directory()));
    return region;
}

ErrorOr<NonnullOwnPtr<Region>> MemoryManager::allocate_unbacked_region_anywhere(size_t size, size_t alignment)
{
    auto region = TRY(Region::create_unbacked());
    TRY(m_global_data.with([&](auto& global_data) { return global_data.region_tree.place_anywhere(*region, RandomizeVirtualAddress::No, size, alignment); }));
    return region;
}

MemoryManager::SystemMemoryInfo MemoryManager::get_system_memory_info()
{
    return m_global_data.with([&](auto& global_data) {
        auto physical_pages_unused = global_data.system_memory_info.physical_pages_committed + global_data.system_memory_info.physical_pages_uncommitted;
        VERIFY(global_data.system_memory_info.physical_pages == (global_data.system_memory_info.physical_pages_used + physical_pages_unused));
        return global_data.system_memory_info;
    });
}
}