Implement CreateBufferMapped for non-mappable buffers

This uses an intermediate staging buffer to copy data into the buffer.

Bug: dawn:7
Change-Id: I3bda19a8450ef0eddc5b4382ce1b9120f074b917
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/7500
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/Buffer.cpp

@@ -43,7 +43,16 @@ namespace dawn_native {
                 return buffer;
             }
 
+            void ClearMappedData() {
+                mFakeMappedData.reset();
+            }
+
           private:
+            bool IsMapWritable() const override {
+                UNREACHABLE();
+                return false;
+            }
+
             MaybeError MapAtCreationImpl(uint8_t** mappedPointer) override {
                 UNREACHABLE();
                 return {};
@@ -62,8 +71,7 @@ namespace dawn_native {
                 UNREACHABLE();
             }
             void UnmapImpl() override {
-                ASSERT(mFakeMappedData);
+                UNREACHABLE();
-                mFakeMappedData.reset();
             }
             void DestroyImpl() override {
                 UNREACHABLE();
@@ -131,7 +139,7 @@ namespace dawn_native {
         return ErrorBuffer::MakeMapped(device, size, mappedPointer);
     }
 
-    uint32_t BufferBase::GetSize() const {
+    uint64_t BufferBase::GetSize() const {
         ASSERT(!IsError());
         return mSize;
     }
@@ -146,13 +154,23 @@ namespace dawn_native {
         ASSERT(mappedPointer != nullptr);
 
         mState = BufferState::Mapped;
-        if ((mUsage & dawn::BufferUsageBit::MapWrite) == 0) {
+
-            // TODO(enga): Support non-mappable buffers with a staging buffer.
+        if (IsMapWritable()) {
-            return DAWN_VALIDATION_ERROR("MapWrite usage required");
+            DAWN_TRY(MapAtCreationImpl(mappedPointer));
+            ASSERT(*mappedPointer != nullptr);
+            return {};
         }
 
-        DAWN_TRY(MapAtCreationImpl(mappedPointer));
+        // If any of these fail, the buffer will be deleted and replaced with an
-        ASSERT(*mappedPointer != nullptr);
+        // error buffer.
+        // TODO(enga): Suballocate and reuse memory from a larger staging buffer so we don't create
+        // many small buffers.
+        DynamicUploader* uploader = nullptr;
+        DAWN_TRY_ASSIGN(uploader, GetDevice()->GetDynamicUploader());
+        DAWN_TRY_ASSIGN(mStagingBuffer, uploader->CreateStagingBuffer(GetSize()));
+
+        ASSERT(mStagingBuffer->GetMappedPointer() != nullptr);
+        *mappedPointer = reinterpret_cast<uint8_t*>(mStagingBuffer->GetMappedPointer());
 
         return {};
     }
@@ -268,33 +286,58 @@ namespace dawn_native {
     }
 
     void BufferBase::Destroy() {
+        if (IsError()) {
+            // It is an error to call Destroy() on an ErrorBuffer, but we still need to reclaim the
+            // fake mapped staging data.
+            reinterpret_cast<ErrorBuffer*>(this)->ClearMappedData();
+        }
         if (GetDevice()->ConsumedError(ValidateDestroy())) {
             return;
         }
         ASSERT(!IsError());
 
         if (mState == BufferState::Mapped) {
-            Unmap();
+            if (mStagingBuffer == nullptr) {
+                Unmap();
+            }
+            mStagingBuffer.reset();
         }
         DestroyInternal();
     }
 
+    MaybeError BufferBase::CopyFromStagingBuffer() {
+        ASSERT(mStagingBuffer);
+        DAWN_TRY(GetDevice()->CopyFromStagingToBuffer(mStagingBuffer.get(), 0, this, 0, GetSize()));
+
+        DynamicUploader* uploader = nullptr;
+        DAWN_TRY_ASSIGN(uploader, GetDevice()->GetDynamicUploader());
+        uploader->ReleaseStagingBuffer(std::move(mStagingBuffer));
+
+        return {};
+    }
+
     void BufferBase::Unmap() {
         if (IsError()) {
             // It is an error to call Unmap() on an ErrorBuffer, but we still need to reclaim the
             // fake mapped staging data.
-            UnmapImpl();
+            reinterpret_cast<ErrorBuffer*>(this)->ClearMappedData();
         }
         if (GetDevice()->ConsumedError(ValidateUnmap())) {
             return;
         }
         ASSERT(!IsError());
 
-        // A map request can only be called once, so this will fire only if the request wasn't
+        if (mStagingBuffer != nullptr) {
-        // completed before the Unmap
+            GetDevice()->ConsumedError(CopyFromStagingBuffer());
-        CallMapReadCallback(mMapSerial, DAWN_BUFFER_MAP_ASYNC_STATUS_UNKNOWN, nullptr, 0u);
+        } else {
-        CallMapWriteCallback(mMapSerial, DAWN_BUFFER_MAP_ASYNC_STATUS_UNKNOWN, nullptr, 0u);
+            // A map request can only be called once, so this will fire only if the request wasn't
-        UnmapImpl();
+            // completed before the Unmap.
+            // Callbacks are not fired if there is no callback registered, so this is correct for
+            // CreateBufferMapped.
+            CallMapReadCallback(mMapSerial, DAWN_BUFFER_MAP_ASYNC_STATUS_UNKNOWN, nullptr, 0u);
+            CallMapWriteCallback(mMapSerial, DAWN_BUFFER_MAP_ASYNC_STATUS_UNKNOWN, nullptr, 0u);
+            UnmapImpl();
+        }
         mState = BufferState::Unmapped;
         mMapReadCallback = nullptr;
         mMapWriteCallback = nullptr;
@@ -304,12 +347,13 @@ namespace dawn_native {
     MaybeError BufferBase::ValidateSetSubData(uint32_t start, uint32_t count) const {
         DAWN_TRY(GetDevice()->ValidateObject(this));
 
-        if (mState == BufferState::Destroyed) {
+        switch (mState) {
-            return DAWN_VALIDATION_ERROR("Buffer is destroyed");
+            case BufferState::Mapped:
-        }
+                return DAWN_VALIDATION_ERROR("Buffer is mapped");
-
+            case BufferState::Destroyed:
-        if (mState == BufferState::Mapped) {
+                return DAWN_VALIDATION_ERROR("Buffer is destroyed");
-            return DAWN_VALIDATION_ERROR("Buffer is mapped");
+            case BufferState::Unmapped:
+                break;
         }
 
         if (count > GetSize()) {
@@ -341,12 +385,13 @@ namespace dawn_native {
     MaybeError BufferBase::ValidateMap(dawn::BufferUsageBit requiredUsage) const {
         DAWN_TRY(GetDevice()->ValidateObject(this));
 
-        if (mState == BufferState::Destroyed) {
+        switch (mState) {
-            return DAWN_VALIDATION_ERROR("Buffer is destroyed");
+            case BufferState::Mapped:
-        }
+                return DAWN_VALIDATION_ERROR("Buffer already mapped");
-
+            case BufferState::Destroyed:
-        if (mState == BufferState::Mapped) {
+                return DAWN_VALIDATION_ERROR("Buffer is destroyed");
-            return DAWN_VALIDATION_ERROR("Buffer already mapped");
+            case BufferState::Unmapped:
+                break;
         }
 
         if (!(mUsage & requiredUsage)) {
@@ -359,12 +404,16 @@ namespace dawn_native {
     MaybeError BufferBase::ValidateUnmap() const {
         DAWN_TRY(GetDevice()->ValidateObject(this));
 
-        if ((mUsage & (dawn::BufferUsageBit::MapRead | dawn::BufferUsageBit::MapWrite)) == 0) {
-            return DAWN_VALIDATION_ERROR("Buffer does not have map usage");
-        }
         switch (mState) {
-            case BufferState::Unmapped:
             case BufferState::Mapped:
+                // A buffer may be in the Mapped state if it was created with CreateBufferMapped
+                // even if it did not have a mappable usage.
+                return {};
+            case BufferState::Unmapped:
+                if ((mUsage & (dawn::BufferUsageBit::MapRead | dawn::BufferUsageBit::MapWrite)) ==
+                    0) {
+                    return DAWN_VALIDATION_ERROR("Buffer does not have map usage");
+                }
                 return {};
             case BufferState::Destroyed:
                 return DAWN_VALIDATION_ERROR("Buffer is destroyed");

src/dawn_native/Buffer.h

@@ -49,7 +49,7 @@ namespace dawn_native {
                                            uint64_t size,
                                            uint8_t** mappedPointer);
 
-        uint32_t GetSize() const;
+        uint64_t GetSize() const;
         dawn::BufferUsageBit GetUsage() const;
 
         MaybeError MapAtCreation(uint8_t** mappedPointer);
@@ -85,6 +85,9 @@ namespace dawn_native {
         virtual void UnmapImpl() = 0;
         virtual void DestroyImpl() = 0;
 
+        virtual bool IsMapWritable() const = 0;
+        MaybeError CopyFromStagingBuffer();
+
         MaybeError ValidateSetSubData(uint32_t start, uint32_t count) const;
         MaybeError ValidateMap(dawn::BufferUsageBit requiredUsage) const;
         MaybeError ValidateUnmap() const;
@@ -98,6 +101,8 @@ namespace dawn_native {
         void* mMapUserdata = 0;
         uint32_t mMapSerial = 0;
 
+        std::unique_ptr<StagingBufferBase> mStagingBuffer;
+
         BufferState mState;
     };
 

src/dawn_native/CommandEncoder.cpp

@@ -484,7 +484,7 @@ namespace dawn_native {
 
                     if (!readOnly && !singleUse) {
                         return DAWN_VALIDATION_ERROR(
-                            "Buffer used as writeable usage and another usage in pass");
+                            "Buffer used as writable usage and another usage in pass");
                     }
                 }
 

src/dawn_native/d3d12/BufferD3D12.cpp

@@ -79,7 +79,10 @@ namespace dawn_native { namespace d3d12 {
         resourceDescriptor.SampleDesc.Count = 1;
         resourceDescriptor.SampleDesc.Quality = 0;
         resourceDescriptor.Layout = D3D12_TEXTURE_LAYOUT_ROW_MAJOR;
-        resourceDescriptor.Flags = D3D12ResourceFlags(GetUsage());
+        // Add TransferDst for non-mappable buffer initialization in CreateBufferMapped
+        // and robust resource initialization.
+        resourceDescriptor.Flags =
+            D3D12ResourceFlags(GetUsage() | dawn::BufferUsageBit::TransferDst);
 
         auto heapType = D3D12HeapType(GetUsage());
         auto bufferUsage = D3D12_RESOURCE_STATE_COMMON;
@@ -160,6 +163,11 @@ namespace dawn_native { namespace d3d12 {
         }
     }
 
+    bool Buffer::IsMapWritable() const {
+        // TODO(enga): Handle CPU-visible memory on UMA
+        return (GetUsage() & (dawn::BufferUsageBit::MapRead | dawn::BufferUsageBit::MapWrite)) != 0;
+    }
+
     MaybeError Buffer::MapAtCreationImpl(uint8_t** mappedPointer) {
         mWrittenMappedRange = {0, GetSize()};
         ASSERT_SUCCESS(

src/dawn_native/d3d12/BufferD3D12.h

@@ -44,6 +44,7 @@ namespace dawn_native { namespace d3d12 {
         void UnmapImpl() override;
         void DestroyImpl() override;
 
+        bool IsMapWritable() const override;
         virtual MaybeError MapAtCreationImpl(uint8_t** mappedPointer) override;
 
         ComPtr<ID3D12Resource> mResource;

src/dawn_native/d3d12/DeviceD3D12.cpp

@@ -71,6 +71,12 @@ namespace dawn_native { namespace d3d12 {
     }
 
     Device::~Device() {
+        // Immediately forget about all pending commands
+        if (mPendingCommands.open) {
+            mPendingCommands.commandList->Close();
+            mPendingCommands.open = false;
+            mPendingCommands.commandList = nullptr;
+        }
         NextSerial();
         WaitForSerial(mLastSubmittedSerial);  // Wait for all in-flight commands to finish executing
         TickImpl();                    // Call tick one last time so resources are cleaned up

src/dawn_native/metal/BufferMTL.h

@@ -40,6 +40,7 @@ namespace dawn_native { namespace metal {
         void UnmapImpl() override;
         void DestroyImpl() override;
 
+        bool IsMapWritable() const override;
         MaybeError MapAtCreationImpl(uint8_t** mappedPointer) override;
 
         id<MTLBuffer> mMtlBuffer = nil;

src/dawn_native/metal/BufferMTL.mm

@@ -47,6 +47,11 @@ namespace dawn_native { namespace metal {
         }
     }
 
+    bool Buffer::IsMapWritable() const {
+        // TODO(enga): Handle CPU-visible memory on UMA
+        return (GetUsage() & (dawn::BufferUsageBit::MapRead | dawn::BufferUsageBit::MapWrite)) != 0;
+    }
+
     MaybeError Buffer::MapAtCreationImpl(uint8_t** mappedPointer) {
         *mappedPointer = reinterpret_cast<uint8_t*>([mMtlBuffer contents]);
         return {};

src/dawn_native/null/DeviceNull.cpp

@@ -56,6 +56,18 @@ namespace dawn_native { namespace null {
         return new Backend(instance);
     }
 
+    struct CopyFromStagingToBufferOperation : PendingOperation {
+        virtual void Execute() {
+            destination->CopyFromStaging(staging, sourceOffset, destinationOffset, size);
+        }
+
+        StagingBufferBase* staging;
+        Buffer* destination;
+        uint64_t sourceOffset;
+        uint64_t destinationOffset;
+        uint64_t size;
+    };
+
     // Device
 
     Device::Device(Adapter* adapter, const DeviceDescriptor* descriptor)
@@ -69,8 +81,7 @@ namespace dawn_native { namespace null {
     Device::~Device() {
         mDynamicUploader = nullptr;
 
-        // Ensure any in-flight maps have been cleaned up.
+        mPendingOperations.clear();
-        SubmitPendingOperations();
         ASSERT(mMemoryUsage == 0);
     }
 
@@ -140,7 +151,16 @@ namespace dawn_native { namespace null {
                                                BufferBase* destination,
                                                uint64_t destinationOffset,
                                                uint64_t size) {
-        return DAWN_UNIMPLEMENTED_ERROR("Device unable to copy from staging buffer.");
+        auto operation = std::make_unique<CopyFromStagingToBufferOperation>();
+        operation->staging = source;
+        operation->destination = reinterpret_cast<Buffer*>(destination);
+        operation->sourceOffset = sourceOffset;
+        operation->destinationOffset = destinationOffset;
+        operation->size = size;
+
+        ToBackend(GetDevice())->AddPendingOperation(std::move(operation));
+
+        return {};
     }
 
     MaybeError Device::IncrementMemoryUsage(size_t bytes) {
@@ -201,8 +221,8 @@ namespace dawn_native { namespace null {
 
     Buffer::Buffer(Device* device, const BufferDescriptor* descriptor)
         : BufferBase(device, descriptor) {
-        if (GetUsage() & (dawn::BufferUsageBit::TransferDst | dawn::BufferUsageBit::MapRead |
+        if (GetUsage() & (dawn::BufferUsageBit::TransferDst | dawn::BufferUsageBit::TransferSrc |
-                          dawn::BufferUsageBit::MapWrite)) {
+                          dawn::BufferUsageBit::MapRead | dawn::BufferUsageBit::MapWrite)) {
             mBackingData = std::unique_ptr<uint8_t[]>(new uint8_t[GetSize()]);
         }
     }
@@ -212,6 +232,12 @@ namespace dawn_native { namespace null {
         ToBackend(GetDevice())->DecrementMemoryUsage(GetSize());
     }
 
+    bool Buffer::IsMapWritable() const {
+        // Only return true for mappable buffers so we can test cases that need / don't need a
+        // staging buffer.
+        return (GetUsage() & (dawn::BufferUsageBit::MapRead | dawn::BufferUsageBit::MapWrite)) != 0;
+    }
+
     MaybeError Buffer::MapAtCreationImpl(uint8_t** mappedPointer) {
         *mappedPointer = mBackingData.get();
         return {};
@@ -225,6 +251,14 @@ namespace dawn_native { namespace null {
         }
     }
 
+    void Buffer::CopyFromStaging(StagingBufferBase* staging,
+                                 uint64_t sourceOffset,
+                                 uint64_t destinationOffset,
+                                 uint64_t size) {
+        uint8_t* ptr = reinterpret_cast<uint8_t*>(staging->GetMappedPointer());
+        memcpy(mBackingData.get() + destinationOffset, ptr + sourceOffset, size);
+    }
+
     MaybeError Buffer::SetSubDataImpl(uint32_t start, uint32_t count, const uint8_t* data) {
         ASSERT(start + count <= GetSize());
         ASSERT(mBackingData);
@@ -243,13 +277,13 @@ namespace dawn_native { namespace null {
     void Buffer::MapAsyncImplCommon(uint32_t serial, bool isWrite) {
         ASSERT(mBackingData);
 
-        auto operation = new BufferMapReadOperation;
+        auto operation = std::make_unique<BufferMapReadOperation>();
         operation->buffer = this;
         operation->ptr = mBackingData.get();
         operation->serial = serial;
         operation->isWrite = isWrite;
 
-        ToBackend(GetDevice())->AddPendingOperation(std::unique_ptr<PendingOperation>(operation));
+        ToBackend(GetDevice())->AddPendingOperation(std::move(operation));
     }
 
     void Buffer::UnmapImpl() {
@@ -324,10 +358,18 @@ namespace dawn_native { namespace null {
 
     // StagingBuffer
 
-    StagingBuffer::StagingBuffer(size_t size, Device* device) : StagingBufferBase(size) {
+    StagingBuffer::StagingBuffer(size_t size, Device* device)
+        : StagingBufferBase(size), mDevice(device) {
+    }
+
+    StagingBuffer::~StagingBuffer() {
+        if (mBuffer) {
+            mDevice->DecrementMemoryUsage(GetSize());
+        }
     }
 
     MaybeError StagingBuffer::Initialize() {
+        DAWN_TRY(mDevice->IncrementMemoryUsage(GetSize()));
         mBuffer = std::make_unique<uint8_t[]>(GetSize());
         mMappedPointer = mBuffer.get();
         return {};

src/dawn_native/null/DeviceNull.h

@@ -142,6 +142,10 @@ namespace dawn_native { namespace null {
         ~Buffer();
 
         void MapReadOperationCompleted(uint32_t serial, void* ptr, bool isWrite);
+        void CopyFromStaging(StagingBufferBase* staging,
+                             uint64_t sourceOffset,
+                             uint64_t destinationOffset,
+                             uint64_t size);
 
       private:
         // Dawn API
@@ -151,6 +155,7 @@ namespace dawn_native { namespace null {
         void UnmapImpl() override;
         void DestroyImpl() override;
 
+        bool IsMapWritable() const override;
         MaybeError MapAtCreationImpl(uint8_t** mappedPointer) override;
         void MapAsyncImplCommon(uint32_t serial, bool isWrite);
 
@@ -201,9 +206,11 @@ namespace dawn_native { namespace null {
     class StagingBuffer : public StagingBufferBase {
       public:
         StagingBuffer(size_t size, Device* device);
+        ~StagingBuffer() override;
         MaybeError Initialize() override;
 
       private:
+        Device* mDevice;
         std::unique_ptr<uint8_t[]> mBuffer;
     };
 

src/dawn_native/opengl/BufferGL.cpp

@@ -35,6 +35,12 @@ namespace dawn_native { namespace opengl {
         return mBuffer;
     }
 
+    bool Buffer::IsMapWritable() const {
+        // TODO(enga): All buffers in GL can be mapped. Investigate if mapping them will cause the
+        // driver to migrate it to shared memory.
+        return true;
+    }
+
     MaybeError Buffer::MapAtCreationImpl(uint8_t** mappedPointer) {
         glBindBuffer(GL_ARRAY_BUFFER, mBuffer);
         void* data = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);

src/dawn_native/opengl/BufferGL.h

@@ -38,6 +38,7 @@ namespace dawn_native { namespace opengl {
         void UnmapImpl() override;
         void DestroyImpl() override;
 
+        bool IsMapWritable() const override;
         MaybeError MapAtCreationImpl(uint8_t** mappedPointer) override;
 
         GLuint mBuffer = 0;

src/dawn_native/vulkan/BufferVk.cpp

@@ -109,7 +109,9 @@ namespace dawn_native { namespace vulkan {
         createInfo.pNext = nullptr;
         createInfo.flags = 0;
         createInfo.size = GetSize();
-        createInfo.usage = VulkanBufferUsage(GetUsage());
+        // Add TransferDst for non-mappable buffer initialization in CreateBufferMapped
+        // and robust resource initialization.
+        createInfo.usage = VulkanBufferUsage(GetUsage() | dawn::BufferUsageBit::TransferDst);
         createInfo.sharingMode = VK_SHARING_MODE_EXCLUSIVE;
         createInfo.queueFamilyIndexCount = 0;
         createInfo.pQueueFamilyIndices = 0;
@@ -188,6 +190,11 @@ namespace dawn_native { namespace vulkan {
         mLastUsage = usage;
     }
 
+    bool Buffer::IsMapWritable() const {
+        // TODO(enga): Handle CPU-visible memory on UMA
+        return mMemoryAllocation.GetMappedPointer() != nullptr;
+    }
+
     MaybeError Buffer::MapAtCreationImpl(uint8_t** mappedPointer) {
         *mappedPointer = mMemoryAllocation.GetMappedPointer();
         return {};

src/dawn_native/vulkan/BufferVk.h

@@ -47,6 +47,7 @@ namespace dawn_native { namespace vulkan {
         void UnmapImpl() override;
         void DestroyImpl() override;
 
+        bool IsMapWritable() const override;
         MaybeError MapAtCreationImpl(uint8_t** mappedPointer) override;
 
         VkBuffer mHandle = VK_NULL_HANDLE;

src/tests/end2end/BufferTests.cpp

@@ -226,10 +226,34 @@ DAWN_INSTANTIATE_TEST(BufferSetSubDataTests,
                      OpenGLBackend,
                      VulkanBackend);
 
-class CreateBufferMappedTests : public DawnTest {};
+class CreateBufferMappedTests : public DawnTest {
+    protected:
+      static void MapReadCallback(DawnBufferMapAsyncStatus status,
+                                  const void* data,
+                                  uint64_t,
+                                  void* userdata) {
+          ASSERT_EQ(DAWN_BUFFER_MAP_ASYNC_STATUS_SUCCESS, status);
+          ASSERT_NE(nullptr, data);
 
-// Test that the simplest CreateBufferMapped works.
+          static_cast<CreateBufferMappedTests*>(userdata)->mappedData = data;
-TEST_P(CreateBufferMappedTests, SmallSyncWrite) {
+      }
+
+      const void* MapReadAsyncAndWait(const dawn::Buffer& buffer) {
+          buffer.MapReadAsync(MapReadCallback, this);
+
+          while (mappedData == nullptr) {
+              WaitABit();
+          }
+
+          return mappedData;
+      }
+
+    private:
+        const void* mappedData = nullptr;
+};
+
+// Test that the simplest CreateBufferMapped works for MapWrite buffers.
+TEST_P(CreateBufferMappedTests, MapWriteUsageSmall) {
     dawn::BufferDescriptor descriptor;
     descriptor.nextInChain = nullptr;
     descriptor.size = 4;
@@ -244,8 +268,42 @@ TEST_P(CreateBufferMappedTests, SmallSyncWrite) {
     EXPECT_BUFFER_U32_EQ(myData, result.buffer, 0);
 }
 
-// Test CreateBufferMapped for a large buffer
+// Test that the simplest CreateBufferMapped works for MapRead buffers.
-TEST_P(CreateBufferMappedTests, LargeSyncWrite) {
+TEST_P(CreateBufferMappedTests, MapReadUsageSmall) {
+    dawn::BufferDescriptor descriptor;
+    descriptor.nextInChain = nullptr;
+    descriptor.size = 4;
+    descriptor.usage = dawn::BufferUsageBit::MapRead;
+
+    uint32_t myData = 230502;
+    dawn::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+    ASSERT_EQ(result.dataLength, descriptor.size);
+    memcpy(result.data, &myData, sizeof(myData));
+    result.buffer.Unmap();
+
+    const void* mappedData = MapReadAsyncAndWait(result.buffer);
+    ASSERT_EQ(myData, *reinterpret_cast<const uint32_t*>(mappedData));
+    result.buffer.Unmap();
+}
+
+// Test that the simplest CreateBufferMapped works for non-mappable buffers.
+TEST_P(CreateBufferMappedTests, NonMappableUsageSmall) {
+    dawn::BufferDescriptor descriptor;
+    descriptor.nextInChain = nullptr;
+    descriptor.size = 4;
+    descriptor.usage = dawn::BufferUsageBit::TransferSrc;
+
+    uint32_t myData = 4239;
+    dawn::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+    ASSERT_EQ(result.dataLength, descriptor.size);
+    memcpy(result.data, &myData, sizeof(myData));
+    result.buffer.Unmap();
+
+    EXPECT_BUFFER_U32_EQ(myData, result.buffer, 0);
+}
+
+// Test CreateBufferMapped for a large MapWrite buffer
+TEST_P(CreateBufferMappedTests, MapWriteUsageLarge) {
     constexpr uint64_t kDataSize = 1000 * 1000;
     std::vector<uint32_t> myData;
     for (uint32_t i = 0; i < kDataSize; ++i) {
@@ -265,9 +323,53 @@ TEST_P(CreateBufferMappedTests, LargeSyncWrite) {
     EXPECT_BUFFER_U32_RANGE_EQ(myData.data(), result.buffer, 0, kDataSize);
 }
 
+// Test CreateBufferMapped for a large MapRead buffer
+TEST_P(CreateBufferMappedTests, MapReadUsageLarge) {
+    constexpr uint64_t kDataSize = 1000 * 1000;
+    std::vector<uint32_t> myData;
+    for (uint32_t i = 0; i < kDataSize; ++i) {
+        myData.push_back(i);
+    }
+
+    dawn::BufferDescriptor descriptor;
+    descriptor.nextInChain = nullptr;
+    descriptor.size = static_cast<uint64_t>(kDataSize * sizeof(uint32_t));
+    descriptor.usage = dawn::BufferUsageBit::MapRead;
+
+    dawn::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+    ASSERT_EQ(result.dataLength, descriptor.size);
+    memcpy(result.data, myData.data(), kDataSize * sizeof(uint32_t));
+    result.buffer.Unmap();
+
+    const void* mappedData = MapReadAsyncAndWait(result.buffer);
+    ASSERT_EQ(0, memcmp(mappedData, myData.data(), kDataSize * sizeof(uint32_t)));
+    result.buffer.Unmap();
+}
+
+// Test CreateBufferMapped for a large non-mappable buffer
+TEST_P(CreateBufferMappedTests, NonMappableUsageLarge) {
+    constexpr uint64_t kDataSize = 1000 * 1000;
+    std::vector<uint32_t> myData;
+    for (uint32_t i = 0; i < kDataSize; ++i) {
+        myData.push_back(i);
+    }
+
+    dawn::BufferDescriptor descriptor;
+    descriptor.nextInChain = nullptr;
+    descriptor.size = static_cast<uint64_t>(kDataSize * sizeof(uint32_t));
+    descriptor.usage = dawn::BufferUsageBit::TransferSrc;
+
+    dawn::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+    ASSERT_EQ(result.dataLength, descriptor.size);
+    memcpy(result.data, myData.data(), kDataSize * sizeof(uint32_t));
+    result.buffer.Unmap();
+
+    EXPECT_BUFFER_U32_RANGE_EQ(myData.data(), result.buffer, 0, kDataSize);
+}
+
 // Test that CreateBufferMapped returns zero-initialized data
 // TODO(enga): This should use the testing toggle to initialize resources to 1.
-TEST_P(CreateBufferMappedTests, ZeroInitialized) {
+TEST_P(CreateBufferMappedTests, MappableZeroInitialized) {
     dawn::BufferDescriptor descriptor;
     descriptor.nextInChain = nullptr;
     descriptor.size = 4;
@@ -279,6 +381,20 @@ TEST_P(CreateBufferMappedTests, ZeroInitialized) {
     result.buffer.Unmap();
 }
 
+// Test that CreateBufferMapped returns zero-initialized data
+// TODO(enga): This should use the testing toggle to initialize resources to 1.
+TEST_P(CreateBufferMappedTests, NonMappableZeroInitialized) {
+    dawn::BufferDescriptor descriptor;
+    descriptor.nextInChain = nullptr;
+    descriptor.size = 4;
+    descriptor.usage = dawn::BufferUsageBit::TransferSrc;
+
+    dawn::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+    ASSERT_EQ(result.dataLength, descriptor.size);
+    ASSERT_EQ(*result.data, 0);
+    result.buffer.Unmap();
+}
+
 // Test that mapping a buffer is valid after CreateBufferMapped and Unmap
 TEST_P(CreateBufferMappedTests, CreateThenMapSuccess) {
     dawn::BufferDescriptor descriptor;

src/tests/unittests/validation/BufferValidationTests.cpp

@@ -198,6 +198,15 @@ TEST_F(BufferValidationTest, CreateBufferMappedSuccess) {
     result.buffer.Unmap();
 }
 
+// Test the success case for non-mappable CreateBufferMapped
+TEST_F(BufferValidationTest, NonMappableCreateBufferMappedSuccess) {
+    dawn::CreateBufferMappedResult result =
+        CreateBufferMapped(4, dawn::BufferUsageBit::TransferSrc);
+    ASSERT_NE(result.data, nullptr);
+    ASSERT_EQ(result.dataLength, 4u);
+    result.buffer.Unmap();
+}
+
 // Test map reading a buffer with wrong current usage
 TEST_F(BufferValidationTest, MapReadWrongUsage) {
     dawn::BufferDescriptor descriptor;
@@ -586,7 +595,7 @@ TEST_F(BufferValidationTest, SetSubDataDestroyedBuffer) {
 }
 
 // Test that is is invalid to Map a mapped buffer
-TEST_F(BufferValidationTest, MapMappedbuffer) {
+TEST_F(BufferValidationTest, MapMappedBuffer) {
     {
         dawn::Buffer buf = CreateMapReadBuffer(4);
         buf.MapReadAsync(ToMockBufferMapReadCallback, nullptr);
@@ -601,6 +610,20 @@ TEST_F(BufferValidationTest, MapMappedbuffer) {
     }
 }
 
+// Test that is is invalid to Map a CreateBufferMapped buffer
+TEST_F(BufferValidationTest, MapCreateBufferMappedBuffer) {
+    {
+        dawn::Buffer buf = CreateBufferMapped(4, dawn::BufferUsageBit::MapRead).buffer;
+        ASSERT_DEVICE_ERROR(buf.MapReadAsync(ToMockBufferMapReadCallback, nullptr));
+        queue.Submit(0, nullptr);
+    }
+    {
+        dawn::Buffer buf = CreateBufferMapped(4, dawn::BufferUsageBit::MapWrite).buffer;
+        ASSERT_DEVICE_ERROR(buf.MapWriteAsync(ToMockBufferMapWriteCallback, nullptr));
+        queue.Submit(0, nullptr);
+    }
+}
+
 // Test that it is invalid to call SetSubData on a mapped buffer
 TEST_F(BufferValidationTest, SetSubDataMappedBuffer) {
     {
@@ -665,6 +688,26 @@ TEST_F(BufferValidationTest, SubmitMappedBuffer) {
 
         bufB.MapReadAsync(ToMockBufferMapReadCallback, nullptr);
 
+        dawn::CommandEncoder encoder = device.CreateCommandEncoder();
+        encoder.CopyBufferToBuffer(bufA, 0, bufB, 0, 4);
+        dawn::CommandBuffer commands = encoder.Finish();
+        ASSERT_DEVICE_ERROR(queue.Submit(1, &commands));
+        queue.Submit(0, nullptr);
+    }
+    {
+        dawn::Buffer bufA = device.CreateBufferMapped(&descriptorA).buffer;
+        dawn::Buffer bufB = device.CreateBuffer(&descriptorB);
+
+        dawn::CommandEncoder encoder = device.CreateCommandEncoder();
+        encoder.CopyBufferToBuffer(bufA, 0, bufB, 0, 4);
+        dawn::CommandBuffer commands = encoder.Finish();
+        ASSERT_DEVICE_ERROR(queue.Submit(1, &commands));
+        queue.Submit(0, nullptr);
+    }
+    {
+        dawn::Buffer bufA = device.CreateBuffer(&descriptorA);
+        dawn::Buffer bufB = device.CreateBufferMapped(&descriptorB).buffer;
+
         dawn::CommandEncoder encoder = device.CreateCommandEncoder();
         encoder.CopyBufferToBuffer(bufA, 0, bufB, 0, 4);
         dawn::CommandBuffer commands = encoder.Finish();