Merge pull request #810 from yuriks/memmap

Kernel: Add VMManager to manage process address spaces

7 files changed, 491 insertions, 38 deletions

diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index 42b4be93..bbc28516 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -36,6 +36,7 @@ set(SRCS
             hle/kernel/shared_memory.cpp
             hle/kernel/thread.cpp
             hle/kernel/timer.cpp
+            hle/kernel/vm_manager.cpp
             hle/service/ac_u.cpp
             hle/service/act_u.cpp
             hle/service/am_app.cpp
@@ -147,6 +148,7 @@ set(HEADERS
             hle/kernel/shared_memory.h
             hle/kernel/thread.h
             hle/kernel/timer.h
+            hle/kernel/vm_manager.h
             hle/result.h
             hle/service/ac_u.h
             hle/service/act_u.h
diff --git a/src/core/hle/kernel/vm_manager.cpp b/src/core/hle/kernel/vm_manager.cpp
new file mode 100644
index 00000000..b2dd2154
--- /dev/null
+++ b/src/core/hle/kernel/vm_manager.cpp
@@ -0,0 +1,245 @@
+// Copyright 2015 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "common/assert.h"
+
+#include "core/hle/kernel/vm_manager.h"
+#include "core/memory_setup.h"
+
+namespace Kernel {
+
+bool VirtualMemoryArea::CanBeMergedWith(const VirtualMemoryArea& next) const {
+    ASSERT(base + size == next.base);
+    if (permissions != next.permissions ||
+            meminfo_state != next.meminfo_state ||
+            type != next.type) {
+        return false;
+    }
+    if (type == VMAType::AllocatedMemoryBlock &&
+            (backing_block != next.backing_block || offset + size != next.offset)) {
+        return false;
+    }
+    if (type == VMAType::BackingMemory && backing_memory + size != next.backing_memory) {
+        return false;
+    }
+    if (type == VMAType::MMIO && paddr + size != next.paddr) {
+        return false;
+    }
+    return true;
+}
+
+VMManager::VMManager() {
+    Reset();
+}
+
+void VMManager::Reset() {
+    vma_map.clear();
+
+    // Initialize the map with a single free region covering the entire managed space.
+    VirtualMemoryArea initial_vma;
+    initial_vma.size = MAX_ADDRESS;
+    vma_map.emplace(initial_vma.base, initial_vma);
+
+    UpdatePageTableForVMA(initial_vma);
+}
+
+VMManager::VMAHandle VMManager::FindVMA(VAddr target) const {
+    return std::prev(vma_map.upper_bound(target));
+}
+
+ResultVal<VMManager::VMAHandle> VMManager::MapMemoryBlock(VAddr target,
+        std::shared_ptr<std::vector<u8>> block, u32 offset, u32 size, MemoryState state) {
+    ASSERT(block != nullptr);
+    ASSERT(offset + size <= block->size());
+
+    // This is the appropriately sized VMA that will turn into our allocation.
+    CASCADE_RESULT(VMAIter vma_handle, CarveVMA(target, size));
+    VirtualMemoryArea& final_vma = vma_handle->second;
+    ASSERT(final_vma.size == size);
+
+    final_vma.type = VMAType::AllocatedMemoryBlock;
+    final_vma.permissions = VMAPermission::ReadWrite;
+    final_vma.meminfo_state = state;
+    final_vma.backing_block = block;
+    final_vma.offset = offset;
+    UpdatePageTableForVMA(final_vma);
+
+    return MakeResult<VMAHandle>(MergeAdjacent(vma_handle));
+}
+
+ResultVal<VMManager::VMAHandle> VMManager::MapBackingMemory(VAddr target, u8 * memory, u32 size, MemoryState state) {
+    ASSERT(memory != nullptr);
+
+    // This is the appropriately sized VMA that will turn into our allocation.
+    CASCADE_RESULT(VMAIter vma_handle, CarveVMA(target, size));
+    VirtualMemoryArea& final_vma = vma_handle->second;
+    ASSERT(final_vma.size == size);
+
+    final_vma.type = VMAType::BackingMemory;
+    final_vma.permissions = VMAPermission::ReadWrite;
+    final_vma.meminfo_state = state;
+    final_vma.backing_memory = memory;
+    UpdatePageTableForVMA(final_vma);
+
+    return MakeResult<VMAHandle>(MergeAdjacent(vma_handle));
+}
+
+ResultVal<VMManager::VMAHandle> VMManager::MapMMIO(VAddr target, PAddr paddr, u32 size, MemoryState state) {
+    // This is the appropriately sized VMA that will turn into our allocation.
+    CASCADE_RESULT(VMAIter vma_handle, CarveVMA(target, size));
+    VirtualMemoryArea& final_vma = vma_handle->second;
+    ASSERT(final_vma.size == size);
+
+    final_vma.type = VMAType::MMIO;
+    final_vma.permissions = VMAPermission::ReadWrite;
+    final_vma.meminfo_state = state;
+    final_vma.paddr = paddr;
+    UpdatePageTableForVMA(final_vma);
+
+    return MakeResult<VMAHandle>(MergeAdjacent(vma_handle));
+}
+
+void VMManager::Unmap(VMAHandle vma_handle) {
+    VMAIter iter = StripIterConstness(vma_handle);
+
+    VirtualMemoryArea& vma = iter->second;
+    vma.type = VMAType::Free;
+    vma.permissions = VMAPermission::None;
+    vma.meminfo_state = MemoryState::Free;
+
+    vma.backing_block = nullptr;
+    vma.offset = 0;
+    vma.backing_memory = nullptr;
+    vma.paddr = 0;
+
+    UpdatePageTableForVMA(vma);
+
+    MergeAdjacent(iter);
+}
+
+void VMManager::Reprotect(VMAHandle vma_handle, VMAPermission new_perms) {
+    VMAIter iter = StripIterConstness(vma_handle);
+
+    VirtualMemoryArea& vma = iter->second;
+    vma.permissions = new_perms;
+    UpdatePageTableForVMA(vma);
+
+    MergeAdjacent(iter);
+}
+
+VMManager::VMAIter VMManager::StripIterConstness(const VMAHandle & iter) {
+    // This uses a neat C++ trick to convert a const_iterator to a regular iterator, given
+    // non-const access to its container.
+    return vma_map.erase(iter, iter); // Erases an empty range of elements
+}
+
+ResultVal<VMManager::VMAIter> VMManager::CarveVMA(VAddr base, u32 size) {
+    ASSERT_MSG((size & Memory::PAGE_MASK) == 0, "non-page aligned size: %8X", size);
+    ASSERT_MSG((base & Memory::PAGE_MASK) == 0, "non-page aligned base: %08X", base);
+
+    VMAIter vma_handle = StripIterConstness(FindVMA(base));
+    if (vma_handle == vma_map.end()) {
+        // Target address is outside the range managed by the kernel
+        return ResultCode(ErrorDescription::InvalidAddress, ErrorModule::OS,
+                ErrorSummary::InvalidArgument, ErrorLevel::Usage); // 0xE0E01BF5
+    }
+
+    VirtualMemoryArea& vma = vma_handle->second;
+    if (vma.type != VMAType::Free) {
+        // Region is already allocated
+        return ResultCode(ErrorDescription::InvalidAddress, ErrorModule::OS,
+                ErrorSummary::InvalidState, ErrorLevel::Usage); // 0xE0A01BF5
+    }
+
+    u32 start_in_vma = base - vma.base;
+    u32 end_in_vma = start_in_vma + size;
+
+    if (end_in_vma > vma.size) {
+        // Requested allocation doesn't fit inside VMA
+        return ResultCode(ErrorDescription::InvalidAddress, ErrorModule::OS,
+                ErrorSummary::InvalidState, ErrorLevel::Usage); // 0xE0A01BF5
+    }
+
+    if (end_in_vma != vma.size) {
+        // Split VMA at the end of the allocated region
+        SplitVMA(vma_handle, end_in_vma);
+    }
+    if (start_in_vma != 0) {
+        // Split VMA at the start of the allocated region
+        vma_handle = SplitVMA(vma_handle, start_in_vma);
+    }
+
+    return MakeResult<VMAIter>(vma_handle);
+}
+
+VMManager::VMAIter VMManager::SplitVMA(VMAIter vma_handle, u32 offset_in_vma) {
+    VirtualMemoryArea& old_vma = vma_handle->second;
+    VirtualMemoryArea new_vma = old_vma; // Make a copy of the VMA
+
+    // For now, don't allow no-op VMA splits (trying to split at a boundary) because it's probably
+    // a bug. This restriction might be removed later.
+    ASSERT(offset_in_vma < old_vma.size);
+    ASSERT(offset_in_vma > 0);
+
+    old_vma.size = offset_in_vma;
+    new_vma.base += offset_in_vma;
+    new_vma.size -= offset_in_vma;
+
+    switch (new_vma.type) {
+    case VMAType::Free:
+        break;
+    case VMAType::AllocatedMemoryBlock:
+        new_vma.offset += offset_in_vma;
+        break;
+    case VMAType::BackingMemory:
+        new_vma.backing_memory += offset_in_vma;
+        break;
+    case VMAType::MMIO:
+        new_vma.paddr += offset_in_vma;
+        break;
+    }
+
+    ASSERT(old_vma.CanBeMergedWith(new_vma));
+
+    return vma_map.emplace_hint(std::next(vma_handle), new_vma.base, new_vma);
+}
+
+VMManager::VMAIter VMManager::MergeAdjacent(VMAIter iter) {
+    VMAIter next_vma = std::next(iter);
+    if (next_vma != vma_map.end() && iter->second.CanBeMergedWith(next_vma->second)) {
+        iter->second.size += next_vma->second.size;
+        vma_map.erase(next_vma);
+    }
+
+    if (iter != vma_map.begin()) {
+        VMAIter prev_vma = std::prev(iter);
+        if (prev_vma->second.CanBeMergedWith(iter->second)) {
+            prev_vma->second.size += iter->second.size;
+            vma_map.erase(iter);
+            iter = prev_vma;
+        }
+    }
+
+    return iter;
+}
+
+void VMManager::UpdatePageTableForVMA(const VirtualMemoryArea& vma) {
+    switch (vma.type) {
+    case VMAType::Free:
+        Memory::UnmapRegion(vma.base, vma.size);
+        break;
+    case VMAType::AllocatedMemoryBlock:
+        Memory::MapMemoryRegion(vma.base, vma.size, vma.backing_block->data() + vma.offset);
+        break;
+    case VMAType::BackingMemory:
+        Memory::MapMemoryRegion(vma.base, vma.size, vma.backing_memory);
+        break;
+    case VMAType::MMIO:
+        // TODO(yuriks): Add support for MMIO handlers.
+        Memory::MapIoRegion(vma.base, vma.size);
+        break;
+    }
+}
+
+}
diff --git a/src/core/hle/kernel/vm_manager.h b/src/core/hle/kernel/vm_manager.h
new file mode 100644
index 00000000..22b72460
--- /dev/null
+++ b/src/core/hle/kernel/vm_manager.h
@@ -0,0 +1,200 @@
+// Copyright 2015 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <map>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "common/common_types.h"
+
+#include "core/hle/result.h"
+
+namespace Kernel {
+
+enum class VMAType : u8 {
+    /// VMA represents an unmapped region of the address space.
+    Free,
+    /// VMA is backed by a ref-counted allocate memory block.
+    AllocatedMemoryBlock,
+    /// VMA is backed by a raw, unmanaged pointer.
+    BackingMemory,
+    /// VMA is mapped to MMIO registers at a fixed PAddr.
+    MMIO,
+    // TODO(yuriks): Implement MemoryAlias to support MAP/UNMAP
+};
+
+/// Permissions for mapped memory blocks
+enum class VMAPermission : u8 {
+    None = 0,
+    Read = 1,
+    Write = 2,
+    Execute = 4,
+
+    ReadWrite = Read | Write,
+    ReadExecute = Read | Execute,
+    WriteExecute = Write | Execute,
+    ReadWriteExecute = Read | Write | Execute,
+};
+
+/// Set of values returned in MemoryInfo.state by svcQueryMemory.
+enum class MemoryState : u8 {
+    Free = 0,
+    Reserved = 1,
+    IO = 2,
+    Static = 3,
+    Code = 4,
+    Private = 5,
+    Shared = 6,
+    Continuous = 7,
+    Aliased = 8,
+    Alias = 9,
+    AliasCode = 10,
+    Locked = 11,
+};
+
+/**
+ * Represents a VMA in an address space. A VMA is a contiguous region of virtual addressing space
+ * with homogeneous attributes across its extents. In this particular implementation each VMA is
+ * also backed by a single host memory allocation.
+ */
+struct VirtualMemoryArea {
+    /// Virtual base address of the region.
+    VAddr base = 0;
+    /// Size of the region.
+    u32 size = 0;
+
+    VMAType type = VMAType::Free;
+    VMAPermission permissions = VMAPermission::None;
+    /// Tag returned by svcQueryMemory. Not otherwise used.
+    MemoryState meminfo_state = MemoryState::Free;
+
+    // Settings for type = AllocatedMemoryBlock
+    /// Memory block backing this VMA.
+    std::shared_ptr<std::vector<u8>> backing_block = nullptr;
+    /// Offset into the backing_memory the mapping starts from.
+    u32 offset = 0;
+
+    // Settings for type = BackingMemory
+    /// Pointer backing this VMA. It will not be destroyed or freed when the VMA is removed.
+    u8* backing_memory = nullptr;
+
+    // Settings for type = MMIO
+    /// Physical address of the register area this VMA maps to.
+    PAddr paddr = 0;
+
+    /// Tests if this area can be merged to the right with `next`.
+    bool CanBeMergedWith(const VirtualMemoryArea& next) const;
+};
+
+/**
+ * Manages a process' virtual addressing space. This class maintains a list of allocated and free
+ * regions in the address space, along with their attributes, and allows kernel clients to
+ * manipulate it, adjusting the page table to match.
+ *
+ * This is similar in idea and purpose to the VM manager present in operating system kernels, with
+ * the main difference being that it doesn't have to support swapping or memory mapping of files.
+ * The implementation is also simplified by not having to allocate page frames. See these articles
+ * about the Linux kernel for an explantion of the concept and implementation:
+ *  - http://duartes.org/gustavo/blog/post/how-the-kernel-manages-your-memory/
+ *  - http://duartes.org/gustavo/blog/post/page-cache-the-affair-between-memory-and-files/
+ */
+class VMManager {
+    // TODO(yuriks): Make page tables switchable to support multiple VMManagers
+public:
+    /**
+     * The maximum amount of address space managed by the kernel. Addresses above this are never used.
+     * @note This is the limit used by the New 3DS kernel. Old 3DS used 0x20000000.
+     */
+    static const u32 MAX_ADDRESS = 0x40000000;
+
+    /**
+     * A map covering the entirety of the managed address space, keyed by the `base` field of each
+     * VMA. It must always be modified by splitting or merging VMAs, so that the invariant
+     * `elem.base + elem.size == next.base` is preserved, and mergeable regions must always be
+     * merged when possible so that no two similar and adjacent regions exist that have not been
+     * merged.
+     */
+    std::map<VAddr, VirtualMemoryArea> vma_map;
+    using VMAHandle = decltype(vma_map)::const_iterator;
+
+    VMManager();
+
+    /// Clears the address space map, re-initializing with a single free area.
+    void Reset();
+
+    /// Finds the VMA in which the given address is included in, or `vma_map.end()`.
+    VMAHandle FindVMA(VAddr target) const;
+
+    // TODO(yuriks): Should these functions actually return the handle?
+
+    /**
+     * Maps part of a ref-counted block of memory at a given address.
+     *
+     * @param target The guest address to start the mapping at.
+     * @param block The block to be mapped.
+     * @param offset Offset into `block` to map from.
+     * @param size Size of the mapping.
+     * @param state MemoryState tag to attach to the VMA.
+     */
+    ResultVal<VMAHandle> MapMemoryBlock(VAddr target, std::shared_ptr<std::vector<u8>> block,
+            u32 offset, u32 size, MemoryState state);
+
+    /**
+     * Maps an unmanaged host memory pointer at a given address.
+     *
+     * @param target The guest address to start the mapping at.
+     * @param memory The memory to be mapped.
+     * @param size Size of the mapping.
+     * @param state MemoryState tag to attach to the VMA.
+     */
+    ResultVal<VMAHandle> MapBackingMemory(VAddr target, u8* memory, u32 size, MemoryState state);
+
+    /**
+     * Maps a memory-mapped IO region at a given address.
+     *
+     * @param target The guest address to start the mapping at.
+     * @param paddr The physical address where the registers are present.
+     * @param size Size of the mapping.
+     * @param state MemoryState tag to attach to the VMA.
+     */
+    ResultVal<VMAHandle> MapMMIO(VAddr target, PAddr paddr, u32 size, MemoryState state);
+
+    /// Unmaps the given VMA.
+    void Unmap(VMAHandle vma);
+
+    /// Changes the permissions of the given VMA.
+    void Reprotect(VMAHandle vma, VMAPermission new_perms);
+
+private:
+    using VMAIter = decltype(vma_map)::iterator;
+
+    /// Converts a VMAHandle to a mutable VMAIter.
+    VMAIter StripIterConstness(const VMAHandle& iter);
+
+    /**
+     * Carves a VMA of a specific size at the specified address by splitting Free VMAs while doing
+     * the appropriate error checking.
+     */
+    ResultVal<VMAIter> CarveVMA(VAddr base, u32 size);
+
+    /**
+     * Splits a VMA in two, at the specified offset.
+     * @returns the right side of the split, with the original iterator becoming the left side.
+     */
+    VMAIter SplitVMA(VMAIter vma, u32 offset_in_vma);
+
+    /**
+     * Checks for and merges the specified VMA with adjacent ones if possible.
+     * @returns the merged VMA or the original if no merging was possible.
+     */
+    VMAIter MergeAdjacent(VMAIter vma);
+
+    /// Updates the pages corresponding to this VMA so they match the VMA's attributes.
+    void UpdatePageTableForVMA(const VirtualMemoryArea& vma);
+};
+
+}
diff --git a/src/core/mem_map.cpp b/src/core/mem_map.cpp
index 5ecec956..bf814b94 100644
--- a/src/core/mem_map.cpp
+++ b/src/core/mem_map.cpp
@@ -8,6 +8,10 @@
 #include "common/logging/log.h"
 
 #include "core/hle/config_mem.h"
+#include "core/hle/kernel/kernel.h"
+#include "core/hle/kernel/shared_memory.h"
+#include "core/hle/kernel/vm_manager.h"
+#include "core/hle/result.h"
 #include "core/hle/shared_page.h"
 #include "core/mem_map.h"
 #include "core/memory.h"
@@ -17,31 +21,23 @@
 
 namespace Memory {
 
-u8* g_exefs_code;  ///< ExeFS:/.code is loaded here
-u8* g_heap;        ///< Application heap (main memory)
-u8* g_shared_mem;  ///< Shared memory
-u8* g_heap_linear; ///< Linear heap
-u8* g_vram;        ///< Video memory (VRAM) pointer
-u8* g_dsp_mem;     ///< DSP memory
-u8* g_tls_mem;     ///< TLS memory
-
 namespace {
 
 struct MemoryArea {
-    u8** ptr;
     u32 base;
     u32 size;
+    const char* name;
 };
 
 // We don't declare the IO regions in here since its handled by other means.
 static MemoryArea memory_areas[] = {
-    {&g_exefs_code,  PROCESS_IMAGE_VADDR, PROCESS_IMAGE_MAX_SIZE},
-    {&g_heap,        HEAP_VADDR,          HEAP_SIZE             },
-    {&g_shared_mem,  SHARED_MEMORY_VADDR, SHARED_MEMORY_SIZE    },
-    {&g_heap_linear, LINEAR_HEAP_VADDR,   LINEAR_HEAP_SIZE      },
-    {&g_vram,        VRAM_VADDR,          VRAM_SIZE             },
-    {&g_dsp_mem,     DSP_RAM_VADDR,       DSP_RAM_SIZE          },
-    {&g_tls_mem,     TLS_AREA_VADDR,      TLS_AREA_SIZE         },
+    {PROCESS_IMAGE_VADDR, PROCESS_IMAGE_MAX_SIZE, "Process Image"}, // ExeFS:/.code is loaded here
+    {HEAP_VADDR,          HEAP_SIZE,              "Heap"},          // Application heap (main memory)
+    {SHARED_MEMORY_VADDR, SHARED_MEMORY_SIZE,     "Shared Memory"}, // Shared memory
+    {LINEAR_HEAP_VADDR,   LINEAR_HEAP_SIZE,       "Linear Heap"},   // Linear heap (main memory)
+    {VRAM_VADDR,          VRAM_SIZE,              "VRAM"},          // Video memory (VRAM)
+    {DSP_RAM_VADDR,       DSP_RAM_SIZE,           "DSP RAM"},       // DSP memory
+    {TLS_AREA_VADDR,      TLS_AREA_SIZE,          "TLS Area"},      // TLS memory
 };
 
 /// Represents a block of memory mapped by ControlMemory/MapMemoryBlock
@@ -135,27 +131,34 @@ VAddr PhysicalToVirtualAddress(const PAddr addr) {
     return addr | 0x80000000;
 }
 
+// TODO(yuriks): Move this into Process
+static Kernel::VMManager address_space;
+
 void Init() {
+    using namespace Kernel;
+
     InitMemoryMap();
 
     for (MemoryArea& area : memory_areas) {
-        *area.ptr = new u8[area.size];
-        MapMemoryRegion(area.base, area.size, *area.ptr);
+        auto block = std::make_shared<std::vector<u8>>(area.size);
+        address_space.MapMemoryBlock(area.base, std::move(block), 0, area.size, MemoryState::Private).Unwrap();
     }
-    MapMemoryRegion(CONFIG_MEMORY_VADDR, CONFIG_MEMORY_SIZE, (u8*)&ConfigMem::config_mem);
-    MapMemoryRegion(SHARED_PAGE_VADDR, SHARED_PAGE_SIZE, (u8*)&SharedPage::shared_page);
 
-    LOG_DEBUG(HW_Memory, "initialized OK, RAM at %p", g_heap);
+    auto cfg_mem_vma = address_space.MapBackingMemory(CONFIG_MEMORY_VADDR,
+            (u8*)&ConfigMem::config_mem, CONFIG_MEMORY_SIZE, MemoryState::Shared).MoveFrom();
+    address_space.Reprotect(cfg_mem_vma, VMAPermission::Read);
+
+    auto shared_page_vma = address_space.MapBackingMemory(SHARED_PAGE_VADDR,
+            (u8*)&SharedPage::shared_page, SHARED_PAGE_SIZE, MemoryState::Shared).MoveFrom();
+    address_space.Reprotect(shared_page_vma, VMAPermission::Read);
+
+    LOG_DEBUG(HW_Memory, "initialized OK");
 }
 
 void Shutdown() {
     heap_map.clear();
     heap_linear_map.clear();
-
-    for (MemoryArea& area : memory_areas) {
-        delete[] *area.ptr;
-        *area.ptr = nullptr;
-    }
+    address_space.Reset();
 
     LOG_DEBUG(HW_Memory, "shutdown OK");
 }
diff --git a/src/core/mem_map.h b/src/core/mem_map.h
index 945815cd..ba50914a 100644
--- a/src/core/mem_map.h
+++ b/src/core/mem_map.h
@@ -8,14 +8,6 @@
 
 namespace Memory {
 
-extern u8* g_exefs_code;  ///< ExeFS:/.code is loaded here
-extern u8* g_heap;        ///< Application heap (main memory)
-extern u8* g_shared_mem;  ///< Shared memory
-extern u8* g_heap_linear; ///< Linear heap (main memory)
-extern u8* g_vram;        ///< Video memory (VRAM)
-extern u8* g_dsp_mem;     ///< DSP memory
-extern u8* g_tls_mem;     ///< TLS memory
-
 void Init();
 void Shutdown();
 
diff --git a/src/core/memory.cpp b/src/core/memory.cpp
index 5d8069ac..28844a91 100644
--- a/src/core/memory.cpp
+++ b/src/core/memory.cpp
@@ -14,12 +14,10 @@
 #include "core/hw/hw.h"
 #include "core/mem_map.h"
 #include "core/memory.h"
+#include "core/memory_setup.h"
 
 namespace Memory {
 
-const u32 PAGE_MASK = PAGE_SIZE - 1;
-const int PAGE_BITS = 12;
-
 enum class PageType {
     /// Page is unmapped and should cause an access error.
     Unmapped,
@@ -64,7 +62,7 @@ static void MapPages(u32 base, u32 size, u8* memory, PageType type) {
     while (base != end) {
         ASSERT_MSG(base < PageTable::NUM_ENTRIES, "out of range mapping at %08X", base);
 
-        if (current_page_table->attributes[base] != PageType::Unmapped) {
+        if (current_page_table->attributes[base] != PageType::Unmapped && type != PageType::Unmapped) {
             LOG_ERROR(HW_Memory, "overlapping memory ranges at %08X", base * PAGE_SIZE);
         }
         current_page_table->attributes[base] = type;
@@ -92,6 +90,12 @@ void MapIoRegion(VAddr base, u32 size) {
     MapPages(base / PAGE_SIZE, size / PAGE_SIZE, nullptr, PageType::Special);
 }
 
+void UnmapRegion(VAddr base, u32 size) {
+    ASSERT_MSG((size & PAGE_MASK) == 0, "non-page aligned size: %08X", size);
+    ASSERT_MSG((base & PAGE_MASK) == 0, "non-page aligned base: %08X", base);
+    MapPages(base / PAGE_SIZE, size / PAGE_SIZE, nullptr, PageType::Unmapped);
+}
+
 template <typename T>
 T Read(const VAddr vaddr) {
     const u8* page_pointer = current_page_table->pointers[vaddr >> PAGE_BITS];
diff --git a/src/core/memory_setup.h b/src/core/memory_setup.h
index 46263495..361bfc81 100644
--- a/src/core/memory_setup.h
+++ b/src/core/memory_setup.h
@@ -6,8 +6,13 @@
 
 #include "common/common_types.h"
 
+#include "core/memory.h"
+
 namespace Memory {
 
+const u32 PAGE_MASK = PAGE_SIZE - 1;
+const int PAGE_BITS = 12;
+
 void InitMemoryMap();
 
 /**
@@ -26,4 +31,6 @@ void MapMemoryRegion(VAddr base, u32 size, u8* target);
  */
 void MapIoRegion(VAddr base, u32 size);
 
+void UnmapRegion(VAddr base, u32 size);
+
 }