6 files changed, 624 insertions, 0 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index 2d403d471..97fbdcbf9 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -131,6 +131,8 @@ add_library(common STATIC
     hash.h
     hex_util.cpp
     hex_util.h
+    host_memory.cpp
+    host_memory.h
     intrusive_red_black_tree.h
     logging/backend.cpp
     logging/backend.h
diff --git a/src/common/host_memory.cpp b/src/common/host_memory.cpp
new file mode 100644
index 000000000..8bd70abc7
--- /dev/null
+++ b/src/common/host_memory.cpp
@@ -0,0 +1,538 @@
+#ifdef _WIN32
+
+#include <iterator>
+#include <unordered_map>
+#include <boost/icl/separate_interval_set.hpp>
+#include <windows.h>
+#include "common/dynamic_library.h"
+
+#elif defined(__linux__) // ^^^ Windows ^^^ vvv Linux vvv
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#endif // ^^^ Linux ^^^
+
+#include <mutex>
+
+#include "common/alignment.h"
+#include "common/assert.h"
+#include "common/host_memory.h"
+#include "common/logging/log.h"
+#include "common/scope_exit.h"
+
+namespace Common {
+
+constexpr size_t PageAlignment = 0x1000;
+constexpr size_t HugePageSize = 0x200000;
+
+#ifdef _WIN32
+
+// Manually imported for MinGW compatibility
+#ifndef MEM_RESERVE_PLACEHOLDER
+#define MEM_RESERVE_PLACEHOLDER 0x0004000
+#endif
+#ifndef MEM_REPLACE_PLACEHOLDER
+#define MEM_REPLACE_PLACEHOLDER 0x00004000
+#endif
+#ifndef MEM_COALESCE_PLACEHOLDERS
+#define MEM_COALESCE_PLACEHOLDERS 0x00000001
+#endif
+#ifndef MEM_PRESERVE_PLACEHOLDER
+#define MEM_PRESERVE_PLACEHOLDER 0x00000002
+#endif
+
+using PFN_CreateFileMapping2 = _Ret_maybenull_ HANDLE(WINAPI*)(
+    _In_ HANDLE File, _In_opt_ SECURITY_ATTRIBUTES* SecurityAttributes, _In_ ULONG DesiredAccess,
+    _In_ ULONG PageProtection, _In_ ULONG AllocationAttributes, _In_ ULONG64 MaximumSize,
+    _In_opt_ PCWSTR Name,
+    _Inout_updates_opt_(ParameterCount) MEM_EXTENDED_PARAMETER* ExtendedParameters,
+    _In_ ULONG ParameterCount);
+
+using PFN_VirtualAlloc2 = _Ret_maybenull_ PVOID(WINAPI*)(
+    _In_opt_ HANDLE Process, _In_opt_ PVOID BaseAddress, _In_ SIZE_T Size,
+    _In_ ULONG AllocationType, _In_ ULONG PageProtection,
+    _Inout_updates_opt_(ParameterCount) MEM_EXTENDED_PARAMETER* ExtendedParameters,
+    _In_ ULONG ParameterCount);
+
+using PFN_MapViewOfFile3 = _Ret_maybenull_ PVOID(WINAPI*)(
+    _In_ HANDLE FileMapping, _In_opt_ HANDLE Process, _In_opt_ PVOID BaseAddress,
+    _In_ ULONG64 Offset, _In_ SIZE_T ViewSize, _In_ ULONG AllocationType, _In_ ULONG PageProtection,
+    _Inout_updates_opt_(ParameterCount) MEM_EXTENDED_PARAMETER* ExtendedParameters,
+    _In_ ULONG ParameterCount);
+
+using PFN_UnmapViewOfFile2 = BOOL(WINAPI*)(_In_ HANDLE Process, _In_ PVOID BaseAddress,
+                                           _In_ ULONG UnmapFlags);
+
+template <typename T>
+static void GetFuncAddress(Common::DynamicLibrary& dll, const char* name, T& pfn) {
+    if (!dll.GetSymbol(name, &pfn)) {
+        LOG_CRITICAL(HW_Memory, "Failed to load {}", name);
+        throw std::bad_alloc{};
+    }
+}
+
+class HostMemory::Impl {
+public:
+    explicit Impl(size_t backing_size_, size_t virtual_size_)
+        : backing_size{backing_size_}, virtual_size{virtual_size_}, process{GetCurrentProcess()},
+          kernelbase_dll("Kernelbase") {
+        if (!kernelbase_dll.IsOpen()) {
+            LOG_CRITICAL(HW_Memory, "Failed to load Kernelbase.dll");
+            throw std::bad_alloc{};
+        }
+        GetFuncAddress(kernelbase_dll, "CreateFileMapping2", pfn_CreateFileMapping2);
+        GetFuncAddress(kernelbase_dll, "VirtualAlloc2", pfn_VirtualAlloc2);
+        GetFuncAddress(kernelbase_dll, "MapViewOfFile3", pfn_MapViewOfFile3);
+        GetFuncAddress(kernelbase_dll, "UnmapViewOfFile2", pfn_UnmapViewOfFile2);
+
+        // Allocate backing file map
+        backing_handle =
+            pfn_CreateFileMapping2(INVALID_HANDLE_VALUE, nullptr, FILE_MAP_WRITE | FILE_MAP_READ,
+                                   PAGE_READWRITE, SEC_COMMIT, backing_size, nullptr, nullptr, 0);
+        if (!backing_handle) {
+            LOG_CRITICAL(HW_Memory, "Failed to allocate {} MiB of backing memory",
+                         backing_size >> 20);
+            throw std::bad_alloc{};
+        }
+        // Allocate a virtual memory for the backing file map as placeholder
+        backing_base = static_cast<u8*>(pfn_VirtualAlloc2(process, nullptr, backing_size,
+                                                          MEM_RESERVE | MEM_RESERVE_PLACEHOLDER,
+                                                          PAGE_NOACCESS, nullptr, 0));
+        if (!backing_base) {
+            Release();
+            LOG_CRITICAL(HW_Memory, "Failed to reserve {} MiB of virtual memory",
+                         backing_size >> 20);
+            throw std::bad_alloc{};
+        }
+        // Map backing placeholder
+        void* const ret = pfn_MapViewOfFile3(backing_handle, process, backing_base, 0, backing_size,
+                                             MEM_REPLACE_PLACEHOLDER, PAGE_READWRITE, nullptr, 0);
+        if (ret != backing_base) {
+            Release();
+            LOG_CRITICAL(HW_Memory, "Failed to map {} MiB of virtual memory", backing_size >> 20);
+            throw std::bad_alloc{};
+        }
+        // Allocate virtual address placeholder
+        virtual_base = static_cast<u8*>(pfn_VirtualAlloc2(process, nullptr, virtual_size,
+                                                          MEM_RESERVE | MEM_RESERVE_PLACEHOLDER,
+                                                          PAGE_NOACCESS, nullptr, 0));
+        if (!virtual_base) {
+            Release();
+            LOG_CRITICAL(HW_Memory, "Failed to reserve {} GiB of virtual memory",
+                         virtual_size >> 30);
+            throw std::bad_alloc{};
+        }
+    }
+
+    ~Impl() {
+        Release();
+    }
+
+    void Map(size_t virtual_offset, size_t host_offset, size_t length) {
+        std::unique_lock lock{placeholder_mutex};
+        if (!IsNiechePlaceholder(virtual_offset, length)) {
+            Split(virtual_offset, length);
+        }
+        ASSERT(placeholders.find({virtual_offset, virtual_offset + length}) == placeholders.end());
+        TrackPlaceholder(virtual_offset, host_offset, length);
+
+        MapView(virtual_offset, host_offset, length);
+    }
+
+    void Unmap(size_t virtual_offset, size_t length) {
+        std::lock_guard lock{placeholder_mutex};
+
+        // Unmap until there are no more placeholders
+        while (UnmapOnePlaceholder(virtual_offset, length)) {
+        }
+    }
+
+    void Protect(size_t virtual_offset, size_t length, bool read, bool write) {
+        DWORD new_flags{};
+        if (read && write) {
+            new_flags = PAGE_READWRITE;
+        } else if (read && !write) {
+            new_flags = PAGE_READONLY;
+        } else if (!read && !write) {
+            new_flags = PAGE_NOACCESS;
+        } else {
+            UNIMPLEMENTED_MSG("Protection flag combination read={} write={}", read, write);
+        }
+        const size_t virtual_end = virtual_offset + length;
+
+        std::lock_guard lock{placeholder_mutex};
+        auto [it, end] = placeholders.equal_range({virtual_offset, virtual_end});
+        while (it != end) {
+            const size_t offset = std::max(it->lower(), virtual_offset);
+            const size_t protect_length = std::min(it->upper(), virtual_end) - offset;
+            DWORD old_flags{};
+            if (!VirtualProtect(virtual_base + offset, protect_length, new_flags, &old_flags)) {
+                LOG_CRITICAL(HW_Memory, "Failed to change virtual memory protect rules");
+            }
+            ++it;
+        }
+    }
+
+    const size_t backing_size; ///< Size of the backing memory in bytes
+    const size_t virtual_size; ///< Size of the virtual address placeholder in bytes
+
+    u8* backing_base{};
+    u8* virtual_base{};
+
+private:
+    /// Release all resources in the object
+    void Release() {
+        if (!placeholders.empty()) {
+            for (const auto& placeholder : placeholders) {
+                if (!pfn_UnmapViewOfFile2(process, virtual_base + placeholder.lower(),
+                                          MEM_PRESERVE_PLACEHOLDER)) {
+                    LOG_CRITICAL(HW_Memory, "Failed to unmap virtual memory placeholder");
+                }
+            }
+            Coalesce(0, virtual_size);
+        }
+        if (virtual_base) {
+            if (!VirtualFree(virtual_base, 0, MEM_RELEASE)) {
+                LOG_CRITICAL(HW_Memory, "Failed to free virtual memory");
+            }
+        }
+        if (backing_base) {
+            if (!pfn_UnmapViewOfFile2(process, backing_base, MEM_PRESERVE_PLACEHOLDER)) {
+                LOG_CRITICAL(HW_Memory, "Failed to unmap backing memory placeholder");
+            }
+            if (!VirtualFreeEx(process, backing_base, 0, MEM_RELEASE)) {
+                LOG_CRITICAL(HW_Memory, "Failed to free backing memory");
+            }
+        }
+        if (!CloseHandle(backing_handle)) {
+            LOG_CRITICAL(HW_Memory, "Failed to free backing memory file handle");
+        }
+    }
+
+    /// Unmap one placeholder in the given range (partial unmaps are supported)
+    /// Return true when there are no more placeholders to unmap
+    bool UnmapOnePlaceholder(size_t virtual_offset, size_t length) {
+        const auto it = placeholders.find({virtual_offset, virtual_offset + length});
+        const auto begin = placeholders.begin();
+        const auto end = placeholders.end();
+        if (it == end) {
+            return false;
+        }
+        const size_t placeholder_begin = it->lower();
+        const size_t placeholder_end = it->upper();
+        const size_t unmap_begin = std::max(virtual_offset, placeholder_begin);
+        const size_t unmap_end = std::min(virtual_offset + length, placeholder_end);
+        ASSERT(unmap_begin >= placeholder_begin && unmap_begin < placeholder_end);
+        ASSERT(unmap_end <= placeholder_end && unmap_end > placeholder_begin);
+
+        const auto host_pointer_it = placeholder_host_pointers.find(placeholder_begin);
+        ASSERT(host_pointer_it != placeholder_host_pointers.end());
+        const size_t host_offset = host_pointer_it->second;
+
+        const bool split_left = unmap_begin > placeholder_begin;
+        const bool split_right = unmap_end < placeholder_end;
+
+        if (!pfn_UnmapViewOfFile2(process, virtual_base + placeholder_begin,
+                                  MEM_PRESERVE_PLACEHOLDER)) {
+            LOG_CRITICAL(HW_Memory, "Failed to unmap placeholder");
+        }
+        // If we have to remap memory regions due to partial unmaps, we are in a data race as
+        // Windows doesn't support remapping memory without unmapping first. Avoid adding any extra
+        // logic within the panic region described below.
+
+        // Panic region, we are in a data race right now
+        if (split_left || split_right) {
+            Split(unmap_begin, unmap_end - unmap_begin);
+        }
+        if (split_left) {
+            MapView(placeholder_begin, host_offset, unmap_begin - placeholder_begin);
+        }
+        if (split_right) {
+            MapView(unmap_end, host_offset + unmap_end - placeholder_begin,
+                    placeholder_end - unmap_end);
+        }
+        // End panic region
+
+        size_t coalesce_begin = unmap_begin;
+        if (!split_left) {
+            // Try to coalesce pages to the left
+            coalesce_begin = it == begin ? 0 : std::prev(it)->upper();
+            if (coalesce_begin != placeholder_begin) {
+                Coalesce(coalesce_begin, unmap_end - coalesce_begin);
+            }
+        }
+        if (!split_right) {
+            // Try to coalesce pages to the right
+            const auto next = std::next(it);
+            const size_t next_begin = next == end ? virtual_size : next->lower();
+            if (placeholder_end != next_begin) {
+                // We can coalesce to the right
+                Coalesce(coalesce_begin, next_begin - coalesce_begin);
+            }
+        }
+        // Remove and reinsert placeholder trackers
+        UntrackPlaceholder(it);
+        if (split_left) {
+            TrackPlaceholder(placeholder_begin, host_offset, unmap_begin - placeholder_begin);
+        }
+        if (split_right) {
+            TrackPlaceholder(unmap_end, host_offset + unmap_end - placeholder_begin,
+                             placeholder_end - unmap_end);
+        }
+        return true;
+    }
+
+    void MapView(size_t virtual_offset, size_t host_offset, size_t length) {
+        if (!pfn_MapViewOfFile3(backing_handle, process, virtual_base + virtual_offset, host_offset,
+                                length, MEM_REPLACE_PLACEHOLDER, PAGE_READWRITE, nullptr, 0)) {
+            LOG_CRITICAL(HW_Memory, "Failed to map placeholder");
+        }
+    }
+
+    void Split(size_t virtual_offset, size_t length) {
+        if (!VirtualFreeEx(process, reinterpret_cast<LPVOID>(virtual_base + virtual_offset), length,
+                           MEM_RELEASE | MEM_PRESERVE_PLACEHOLDER)) {
+            LOG_CRITICAL(HW_Memory, "Failed to split placeholder");
+        }
+    }
+
+    void Coalesce(size_t virtual_offset, size_t length) {
+        if (!VirtualFreeEx(process, reinterpret_cast<LPVOID>(virtual_base + virtual_offset), length,
+                           MEM_RELEASE | MEM_COALESCE_PLACEHOLDERS)) {
+            LOG_CRITICAL(HW_Memory, "Failed to coalesce placeholders");
+        }
+    }
+
+    void TrackPlaceholder(size_t virtual_offset, size_t host_offset, size_t length) {
+        placeholders.insert({virtual_offset, virtual_offset + length});
+        placeholder_host_pointers.emplace(virtual_offset, host_offset);
+    }
+
+    void UntrackPlaceholder(boost::icl::separate_interval_set<size_t>::iterator it) {
+        placeholders.erase(it);
+        placeholder_host_pointers.erase(it->lower());
+    }
+
+    /// Return true when a given memory region is a "nieche" and the placeholders don't have to be
+    /// splitted.
+    bool IsNiechePlaceholder(size_t virtual_offset, size_t length) const {
+        const auto it = placeholders.upper_bound({virtual_offset, virtual_offset + length});
+        if (it != placeholders.end() && it->lower() == virtual_offset + length) {
+            const bool is_root = it == placeholders.begin() && virtual_offset == 0;
+            return is_root || std::prev(it)->upper() == virtual_offset;
+        }
+        return false;
+    }
+
+    HANDLE process{};        ///< Current process handle
+    HANDLE backing_handle{}; ///< File based backing memory
+
+    DynamicLibrary kernelbase_dll;
+    PFN_CreateFileMapping2 pfn_CreateFileMapping2{};
+    PFN_VirtualAlloc2 pfn_VirtualAlloc2{};
+    PFN_MapViewOfFile3 pfn_MapViewOfFile3{};
+    PFN_UnmapViewOfFile2 pfn_UnmapViewOfFile2{};
+
+    std::mutex placeholder_mutex;                                 ///< Mutex for placeholders
+    boost::icl::separate_interval_set<size_t> placeholders;       ///< Mapped placeholders
+    std::unordered_map<size_t, size_t> placeholder_host_pointers; ///< Placeholder backing offset
+};
+
+#elif defined(__linux__) // ^^^ Windows ^^^ vvv Linux vvv
+
+class HostMemory::Impl {
+public:
+    explicit Impl(size_t backing_size_, size_t virtual_size_)
+        : backing_size{backing_size_}, virtual_size{virtual_size_} {
+        bool good = false;
+        SCOPE_EXIT({
+            if (!good) {
+                Release();
+            }
+        });
+
+        // Backing memory initialization
+        fd = memfd_create("HostMemory", 0);
+        if (fd == -1) {
+            LOG_CRITICAL(HW_Memory, "memfd_create failed: {}", strerror(errno));
+            throw std::bad_alloc{};
+        }
+
+        // Defined to extend the file with zeros
+        int ret = ftruncate(fd, backing_size);
+        if (ret != 0) {
+            LOG_CRITICAL(HW_Memory, "ftruncate failed with {}, are you out-of-memory?",
+                         strerror(errno));
+            throw std::bad_alloc{};
+        }
+
+        backing_base = static_cast<u8*>(
+            mmap(nullptr, backing_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0));
+        if (backing_base == MAP_FAILED) {
+            LOG_CRITICAL(HW_Memory, "mmap failed: {}", strerror(errno));
+            throw std::bad_alloc{};
+        }
+
+        // Virtual memory initialization
+        virtual_base = static_cast<u8*>(
+            mmap(nullptr, virtual_size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));
+        if (virtual_base == MAP_FAILED) {
+            LOG_CRITICAL(HW_Memory, "mmap failed: {}", strerror(errno));
+            throw std::bad_alloc{};
+        }
+
+        good = true;
+    }
+
+    ~Impl() {
+        Release();
+    }
+
+    void Map(size_t virtual_offset, size_t host_offset, size_t length) {
+
+        void* ret = mmap(virtual_base + virtual_offset, length, PROT_READ | PROT_WRITE,
+                         MAP_SHARED | MAP_FIXED, fd, host_offset);
+        ASSERT_MSG(ret != MAP_FAILED, "mmap failed: {}", strerror(errno));
+    }
+
+    void Unmap(size_t virtual_offset, size_t length) {
+        // The method name is wrong. We're still talking about the virtual range.
+        // We don't want to unmap, we want to reserve this memory.
+
+        void* ret = mmap(virtual_base + virtual_offset, length, PROT_NONE,
+                         MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+        ASSERT_MSG(ret != MAP_FAILED, "mmap failed: {}", strerror(errno));
+    }
+
+    void Protect(size_t virtual_offset, size_t length, bool read, bool write) {
+        int flags = 0;
+        if (read) {
+            flags |= PROT_READ;
+        }
+        if (write) {
+            flags |= PROT_WRITE;
+        }
+        int ret = mprotect(virtual_base + virtual_offset, length, flags);
+        ASSERT_MSG(ret == 0, "mprotect failed: {}", strerror(errno));
+    }
+
+    const size_t backing_size; ///< Size of the backing memory in bytes
+    const size_t virtual_size; ///< Size of the virtual address placeholder in bytes
+
+    u8* backing_base{reinterpret_cast<u8*>(MAP_FAILED)};
+    u8* virtual_base{reinterpret_cast<u8*>(MAP_FAILED)};
+
+private:
+    /// Release all resources in the object
+    void Release() {
+        if (virtual_base != MAP_FAILED) {
+            int ret = munmap(virtual_base, virtual_size);
+            ASSERT_MSG(ret == 0, "munmap failed: {}", strerror(errno));
+        }
+
+        if (backing_base != MAP_FAILED) {
+            int ret = munmap(backing_base, backing_size);
+            ASSERT_MSG(ret == 0, "munmap failed: {}", strerror(errno));
+        }
+
+        if (fd != -1) {
+            int ret = close(fd);
+            ASSERT_MSG(ret == 0, "close failed: {}", strerror(errno));
+        }
+    }
+
+    int fd{-1}; // memfd file descriptor, -1 is the error value of memfd_create
+};
+
+#else // ^^^ Linux ^^^ vvv Generic vvv
+
+class HostMemory::Impl {
+public:
+    explicit Impl(size_t /*backing_size */, size_t /* virtual_size */) {
+        // This is just a place holder.
+        // Please implement fastmem in a propper way on your platform.
+        throw std::bad_alloc{};
+    }
+
+    void Map(size_t virtual_offset, size_t host_offset, size_t length) {}
+
+    void Unmap(size_t virtual_offset, size_t length) {}
+
+    void Protect(size_t virtual_offset, size_t length, bool read, bool write) {}
+
+    u8* backing_base{nullptr};
+    u8* virtual_base{nullptr};
+};
+
+#endif // ^^^ Generic ^^^
+
+HostMemory::HostMemory(size_t backing_size_, size_t virtual_size_)
+    : backing_size(backing_size_), virtual_size(virtual_size_) {
+    try {
+        // Try to allocate a fastmem arena.
+        // The implementation will fail with std::bad_alloc on errors.
+        impl = std::make_unique<HostMemory::Impl>(AlignUp(backing_size, PageAlignment),
+                                                  AlignUp(virtual_size, PageAlignment) +
+                                                      3 * HugePageSize);
+        backing_base = impl->backing_base;
+        virtual_base = impl->virtual_base;
+
+        if (virtual_base) {
+            virtual_base += 2 * HugePageSize - 1;
+            virtual_base -= reinterpret_cast<size_t>(virtual_base) & (HugePageSize - 1);
+            virtual_base_offset = virtual_base - impl->virtual_base;
+        }
+
+    } catch (const std::bad_alloc&) {
+        LOG_CRITICAL(HW_Memory,
+                     "Fastmem unavailable, falling back to VirtualBuffer for memory allocation");
+        fallback_buffer = std::make_unique<Common::VirtualBuffer<u8>>(backing_size);
+        backing_base = fallback_buffer->data();
+        virtual_base = nullptr;
+    }
+}
+
+HostMemory::~HostMemory() = default;
+
+HostMemory::HostMemory(HostMemory&&) noexcept = default;
+
+HostMemory& HostMemory::operator=(HostMemory&&) noexcept = default;
+
+void HostMemory::Map(size_t virtual_offset, size_t host_offset, size_t length) {
+    ASSERT(virtual_offset % PageAlignment == 0);
+    ASSERT(host_offset % PageAlignment == 0);
+    ASSERT(length % PageAlignment == 0);
+    ASSERT(virtual_offset + length <= virtual_size);
+    ASSERT(host_offset + length <= backing_size);
+    if (length == 0 || !virtual_base || !impl) {
+        return;
+    }
+    impl->Map(virtual_offset + virtual_base_offset, host_offset, length);
+}
+
+void HostMemory::Unmap(size_t virtual_offset, size_t length) {
+    ASSERT(virtual_offset % PageAlignment == 0);
+    ASSERT(length % PageAlignment == 0);
+    ASSERT(virtual_offset + length <= virtual_size);
+    if (length == 0 || !virtual_base || !impl) {
+        return;
+    }
+    impl->Unmap(virtual_offset + virtual_base_offset, length);
+}
+
+void HostMemory::Protect(size_t virtual_offset, size_t length, bool read, bool write) {
+    ASSERT(virtual_offset % PageAlignment == 0);
+    ASSERT(length % PageAlignment == 0);
+    ASSERT(virtual_offset + length <= virtual_size);
+    if (length == 0 || !virtual_base || !impl) {
+        return;
+    }
+    impl->Protect(virtual_offset + virtual_base_offset, length, read, write);
+}
+
+} // namespace Common
diff --git a/src/common/host_memory.h b/src/common/host_memory.h
new file mode 100644
index 000000000..9b8326d0f
--- /dev/null
+++ b/src/common/host_memory.h
@@ -0,0 +1,70 @@
+// Copyright 2019 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include "common/common_types.h"
+#include "common/virtual_buffer.h"
+
+namespace Common {
+
+/**
+ * A low level linear memory buffer, which supports multiple mappings
+ * Its purpose is to rebuild a given sparse memory layout, including mirrors.
+ */
+class HostMemory {
+public:
+    explicit HostMemory(size_t backing_size_, size_t virtual_size_);
+    ~HostMemory();
+
+    /**
+     * Copy constructors. They shall return a copy of the buffer without the mappings.
+     * TODO: Implement them with COW if needed.
+     */
+    HostMemory(const HostMemory& other) = delete;
+    HostMemory& operator=(const HostMemory& other) = delete;
+
+    /**
+     * Move constructors. They will move the buffer and the mappings to the new object.
+     */
+    HostMemory(HostMemory&& other) noexcept;
+    HostMemory& operator=(HostMemory&& other) noexcept;
+
+    void Map(size_t virtual_offset, size_t host_offset, size_t length);
+
+    void Unmap(size_t virtual_offset, size_t length);
+
+    void Protect(size_t virtual_offset, size_t length, bool read, bool write);
+
+    [[nodiscard]] u8* BackingBasePointer() noexcept {
+        return backing_base;
+    }
+    [[nodiscard]] const u8* BackingBasePointer() const noexcept {
+        return backing_base;
+    }
+
+    [[nodiscard]] u8* VirtualBasePointer() noexcept {
+        return virtual_base;
+    }
+    [[nodiscard]] const u8* VirtualBasePointer() const noexcept {
+        return virtual_base;
+    }
+
+private:
+    size_t backing_size{};
+    size_t virtual_size{};
+
+    // Low level handler for the platform dependent memory routines
+    class Impl;
+    std::unique_ptr<Impl> impl;
+    u8* backing_base{};
+    u8* virtual_base{};
+    size_t virtual_base_offset{};
+
+    // Fallback if fastmem is not supported on this platform
+    std::unique_ptr<Common::VirtualBuffer<u8>> fallback_buffer;
+};
+
+} // namespace Common
diff --git a/src/common/page_table.h b/src/common/page_table.h
index e92b66b2b..8267e8b4d 100644
--- a/src/common/page_table.h
+++ b/src/common/page_table.h
@@ -111,6 +111,8 @@ struct PageTable {
     VirtualBuffer<u64> backing_addr;
 
     size_t current_address_space_width_in_bits;
+
+    u8* fastmem_arena;
 };
 
 } // namespace Common
diff --git a/src/common/settings.cpp b/src/common/settings.cpp
index bcb4e4be1..360e878d6 100644
--- a/src/common/settings.cpp
+++ b/src/common/settings.cpp
@@ -90,6 +90,13 @@ bool IsGPULevelHigh() {
            values.gpu_accuracy.GetValue() == GPUAccuracy::High;
 }
 
+bool IsFastmemEnabled() {
+    if (values.cpu_accuracy.GetValue() == CPUAccuracy::DebugMode) {
+        return values.cpuopt_fastmem;
+    }
+    return true;
+}
+
 float Volume() {
     if (values.audio_muted) {
         return 0.0f;
@@ -115,6 +122,7 @@ void RestoreGlobalState(bool is_powered_on) {
     values.cpuopt_unsafe_unfuse_fma.SetGlobal(true);
     values.cpuopt_unsafe_reduce_fp_error.SetGlobal(true);
     values.cpuopt_unsafe_inaccurate_nan.SetGlobal(true);
+    values.cpuopt_unsafe_fastmem_check.SetGlobal(true);
 
     // Renderer
     values.renderer_backend.SetGlobal(true);
diff --git a/src/common/settings.h b/src/common/settings.h
index 48085b9a9..1af8c5ac2 100644
--- a/src/common/settings.h
+++ b/src/common/settings.h
@@ -125,10 +125,12 @@ struct Values {
     bool cpuopt_const_prop;
     bool cpuopt_misc_ir;
     bool cpuopt_reduce_misalign_checks;
+    bool cpuopt_fastmem;
 
     Setting<bool> cpuopt_unsafe_unfuse_fma;
     Setting<bool> cpuopt_unsafe_reduce_fp_error;
     Setting<bool> cpuopt_unsafe_inaccurate_nan;
+    Setting<bool> cpuopt_unsafe_fastmem_check;
 
     // Renderer
     Setting<RendererBackend> renderer_backend;
@@ -249,6 +251,8 @@ void SetConfiguringGlobal(bool is_global);
 bool IsGPULevelExtreme();
 bool IsGPULevelHigh();
 
+bool IsFastmemEnabled();
+
 float Volume();
 
 std::string GetTimeZoneString();