Kernel/VirtIO: Introduce the concept of transport options

The VirtIO specification defines many types of devices with different
purposes, and it also defines 3 possible transport mediums where devices
could be connected to the host machine.

We only care about the PCIe transport, but this commit puts the actual
foundations for supporting the lean MMIO transport too in the future.

To ensure things are kept abstracted but still functional, the VirtIO
transport code is responsible for what is deemed as related to an actual
transport type - allocation of interrupt handlers and tinkering with low
level transport-related registers, etc.

Kernel/Bus/VirtIO/Transport/Entity.cpp

@@ -0,0 +1,168 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Bus/VirtIO/Transport/Entity.h>
+
+namespace Kernel::VirtIO {
+
+auto TransportEntity::mapping_for_resource_index(u8 resource_index) -> IOWindow&
+{
+    VERIFY(m_use_mmio);
+    VERIFY(m_register_bases[resource_index]);
+    return *m_register_bases[resource_index];
+}
+
+u8 TransportEntity::config_read8(Configuration const& config, u32 offset)
+{
+    return mapping_for_resource_index(config.resource_index).read8(config.offset + offset);
+}
+
+u16 TransportEntity::config_read16(Configuration const& config, u32 offset)
+{
+    return mapping_for_resource_index(config.resource_index).read16(config.offset + offset);
+}
+
+u32 TransportEntity::config_read32(Configuration const& config, u32 offset)
+{
+    return mapping_for_resource_index(config.resource_index).read32(config.offset + offset);
+}
+
+void TransportEntity::config_write8(Configuration const& config, u32 offset, u8 value)
+{
+    mapping_for_resource_index(config.resource_index).write8(config.offset + offset, value);
+}
+
+void TransportEntity::config_write16(Configuration const& config, u32 offset, u16 value)
+{
+    mapping_for_resource_index(config.resource_index).write16(config.offset + offset, value);
+}
+
+void TransportEntity::config_write32(Configuration const& config, u32 offset, u32 value)
+{
+    mapping_for_resource_index(config.resource_index).write32(config.offset + offset, value);
+}
+
+void TransportEntity::config_write64(Configuration const& config, u32 offset, u64 value)
+{
+    mapping_for_resource_index(config.resource_index).write32(config.offset + offset, (u32)(value & 0xFFFFFFFF));
+    mapping_for_resource_index(config.resource_index).write32(config.offset + offset + 4, (u32)(value >> 32));
+}
+
+IOWindow& TransportEntity::base_io_window()
+{
+    VERIFY(m_register_bases[0]);
+    return *m_register_bases[0];
+}
+
+u8 TransportEntity::isr_status()
+{
+    if (!m_isr_cfg)
+        return base_io_window().read8(REG_ISR_STATUS);
+    return config_read8(*m_isr_cfg, 0);
+}
+
+void TransportEntity::set_status_bits(Badge<VirtIO::Device>, u8 status_bits)
+{
+    return set_status_bits(status_bits);
+}
+
+void TransportEntity::set_status_bits(u8 status_bits)
+{
+    if (!m_common_cfg)
+        base_io_window().write8(REG_DEVICE_STATUS, status_bits);
+    else
+        config_write8(*m_common_cfg, COMMON_CFG_DEVICE_STATUS, status_bits);
+}
+
+ErrorOr<NonnullOwnPtr<Queue>> TransportEntity::setup_queue(Badge<VirtIO::Device>, u16 queue_index)
+{
+    if (!m_common_cfg)
+        return Error::from_errno(ENXIO);
+
+    config_write16(*m_common_cfg, COMMON_CFG_QUEUE_SELECT, queue_index);
+    u16 queue_size = config_read16(*m_common_cfg, COMMON_CFG_QUEUE_SIZE);
+    if (queue_size == 0) {
+        dbgln_if(VIRTIO_DEBUG, "Queue[{}] is unavailable!", queue_index);
+        return Error::from_errno(ENXIO);
+    }
+
+    u16 queue_notify_offset = config_read16(*m_common_cfg, COMMON_CFG_QUEUE_NOTIFY_OFF);
+
+    auto queue = TRY(Queue::try_create(queue_size, queue_notify_offset));
+
+    config_write64(*m_common_cfg, COMMON_CFG_QUEUE_DESC, queue->descriptor_area().get());
+    config_write64(*m_common_cfg, COMMON_CFG_QUEUE_DRIVER, queue->driver_area().get());
+    config_write64(*m_common_cfg, COMMON_CFG_QUEUE_DEVICE, queue->device_area().get());
+    return queue;
+}
+
+void TransportEntity::accept_device_features(Badge<VirtIO::Device>, u64 accepted_features)
+{
+    if (!m_common_cfg) {
+        base_io_window().write32(REG_GUEST_FEATURES, accepted_features);
+    } else {
+        config_write32(*m_common_cfg, COMMON_CFG_DRIVER_FEATURE_SELECT, 0);
+        config_write32(*m_common_cfg, COMMON_CFG_DRIVER_FEATURE, accepted_features);
+        config_write32(*m_common_cfg, COMMON_CFG_DRIVER_FEATURE_SELECT, 1);
+        config_write32(*m_common_cfg, COMMON_CFG_DRIVER_FEATURE, accepted_features >> 32);
+    }
+}
+
+void TransportEntity::reset_device(Badge<VirtIO::Device>)
+{
+    if (!m_common_cfg) {
+        set_status_bits(0);
+        while (read_status_bits() != 0) {
+            // TODO: delay a bit?
+        }
+        return;
+    }
+    config_write8(*m_common_cfg, COMMON_CFG_DEVICE_STATUS, 0);
+    while (config_read8(*m_common_cfg, COMMON_CFG_DEVICE_STATUS) != 0) {
+        // TODO: delay a bit?
+    }
+}
+
+void TransportEntity::notify_queue(Badge<VirtIO::Device>, NotifyQueueDescriptor descriptor)
+{
+    dbgln_if(VIRTIO_DEBUG, "notifying about queue change at idx: {}", descriptor.queue_index);
+    if (!m_notify_cfg)
+        base_io_window().write16(REG_QUEUE_NOTIFY, descriptor.queue_index);
+    else
+        config_write16(*m_notify_cfg, descriptor.possible_notify_offset * m_notify_multiplier, descriptor.queue_index);
+}
+
+bool TransportEntity::activate_queue(Badge<VirtIO::Device>, u16 queue_index)
+{
+    if (!m_common_cfg)
+        return false;
+
+    config_write16(*m_common_cfg, COMMON_CFG_QUEUE_SELECT, queue_index);
+    config_write16(*m_common_cfg, COMMON_CFG_QUEUE_ENABLE, true);
+
+    dbgln_if(VIRTIO_DEBUG, "Queue[{}] activated", queue_index);
+    return true;
+}
+
+u64 TransportEntity::get_device_features()
+{
+    if (!m_common_cfg)
+        return base_io_window().read32(REG_DEVICE_FEATURES);
+    config_write32(*m_common_cfg, COMMON_CFG_DEVICE_FEATURE_SELECT, 0);
+    auto lower_bits = config_read32(*m_common_cfg, COMMON_CFG_DEVICE_FEATURE);
+    config_write32(*m_common_cfg, COMMON_CFG_DEVICE_FEATURE_SELECT, 1);
+    u64 upper_bits = (u64)config_read32(*m_common_cfg, COMMON_CFG_DEVICE_FEATURE) << 32;
+    return upper_bits | lower_bits;
+}
+
+u8 TransportEntity::read_status_bits()
+{
+    if (!m_common_cfg)
+        return base_io_window().read8(REG_DEVICE_STATUS);
+    return config_read8(*m_common_cfg, COMMON_CFG_DEVICE_STATUS);
+}
+
+}

Kernel/Bus/VirtIO/Transport/Entity.h

@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+#include <Kernel/Bus/VirtIO/Definitions.h>
+#include <Kernel/Bus/VirtIO/Queue.h>
+#include <Kernel/Library/IOWindow.h>
+
+namespace Kernel::VirtIO {
+
+class TransportEntity {
+public:
+    virtual ~TransportEntity() = default;
+
+    virtual ErrorOr<void> locate_configurations_and_resources(Badge<VirtIO::Device>, VirtIO::Device&) = 0;
+    virtual void disable_interrupts(Badge<VirtIO::Device>) = 0;
+    virtual void enable_interrupts(Badge<VirtIO::Device>) = 0;
+
+    virtual StringView determine_device_class_name() const = 0;
+
+    void accept_device_features(Badge<VirtIO::Device>, u64 accepted_features);
+
+    struct NotifyQueueDescriptor {
+        u16 queue_index;
+        u16 possible_notify_offset;
+    };
+    void notify_queue(Badge<VirtIO::Device>, NotifyQueueDescriptor);
+    bool activate_queue(Badge<VirtIO::Device>, u16 queue_index);
+    ErrorOr<NonnullOwnPtr<Queue>> setup_queue(Badge<VirtIO::Device>, u16 queue_index);
+    void set_status_bits(Badge<VirtIO::Device>, u8 status_bits);
+    void reset_device(Badge<VirtIO::Device>);
+
+    u8 read_status_bits();
+    u8 isr_status();
+    u64 get_device_features();
+
+    ErrorOr<Configuration const*> get_config(ConfigurationType cfg_type, u32 index = 0) const
+    {
+        for (auto const& cfg : m_configs) {
+            if (cfg.cfg_type != cfg_type)
+                continue;
+            if (index > 0) {
+                index--;
+                continue;
+            }
+            return &cfg;
+        }
+        return Error::from_errno(ENXIO);
+    }
+
+    u8 config_read8(Configuration const&, u32);
+    u16 config_read16(Configuration const&, u32);
+    u32 config_read32(Configuration const&, u32);
+    void config_write8(Configuration const&, u32, u8);
+    void config_write16(Configuration const&, u32, u16);
+    void config_write32(Configuration const&, u32, u32);
+    void config_write64(Configuration const&, u32, u64);
+
+    template<typename F>
+    void read_config_atomic(F f)
+    {
+        if (m_common_cfg) {
+            u8 generation_before, generation_after;
+            do {
+                generation_before = config_read8(*m_common_cfg, 0x15);
+                f();
+                generation_after = config_read8(*m_common_cfg, 0x15);
+            } while (generation_before != generation_after);
+        } else {
+            f();
+        }
+    }
+
+protected:
+    TransportEntity() = default;
+
+    auto mapping_for_resource_index(u8) -> IOWindow&;
+
+    void set_status_bits(u8 status_bits);
+
+    Vector<Configuration> m_configs;
+    Configuration const* m_common_cfg { nullptr }; // Cached due to high usage
+    Configuration const* m_notify_cfg { nullptr }; // Cached due to high usage
+    Configuration const* m_isr_cfg { nullptr };    // Cached due to high usage
+
+    IOWindow& base_io_window();
+    Array<OwnPtr<IOWindow>, 6> m_register_bases;
+    bool m_use_mmio { false };
+
+    u32 m_notify_multiplier { 0 };
+};
+
+};

Kernel/Bus/VirtIO/Transport/InterruptHandler.cpp

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Bus/VirtIO/Device.h>
+#include <Kernel/Bus/VirtIO/Transport/InterruptHandler.h>
+
+namespace Kernel::VirtIO {
+
+TransportInterruptHandler::TransportInterruptHandler(VirtIO::Device& parent_device)
+    : m_parent_device(parent_device)
+{
+}
+
+bool TransportInterruptHandler::notify_parent_device_on_interrupt()
+{
+    return m_parent_device.handle_irq({});
+}
+
+}

Kernel/Bus/VirtIO/Transport/InterruptHandler.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+namespace Kernel::VirtIO {
+
+class Device;
+class TransportInterruptHandler {
+protected:
+    TransportInterruptHandler(VirtIO::Device&);
+
+    bool notify_parent_device_on_interrupt();
+
+private:
+    VirtIO::Device& m_parent_device;
+};
+
+}

Kernel/Bus/VirtIO/Transport/PCIe/Detect.cpp

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Try.h>
+#include <Kernel/Boot/CommandLine.h>
+#include <Kernel/Bus/PCI/API.h>
+#include <Kernel/Bus/PCI/IDs.h>
+#include <Kernel/Bus/VirtIO/Console.h>
+#include <Kernel/Bus/VirtIO/Device.h>
+#include <Kernel/Bus/VirtIO/RNG.h>
+#include <Kernel/Bus/VirtIO/Transport/PCIe/Detect.h>
+#include <Kernel/Sections.h>
+
+namespace Kernel::VirtIO {
+
+UNMAP_AFTER_INIT void detect_pci_instances()
+{
+    if (kernel_command_line().disable_virtio())
+        return;
+    MUST(PCI::enumerate([&](PCI::DeviceIdentifier const& device_identifier) {
+        if (device_identifier.hardware_id().is_null())
+            return;
+        // TODO: We should also be checking that the device_id is in between 0x1000 - 0x107F inclusive
+        if (device_identifier.hardware_id().vendor_id != PCI::VendorID::VirtIO)
+            return;
+        switch (device_identifier.hardware_id().device_id) {
+        case PCI::DeviceID::VirtIOConsole: {
+            auto& console = Console::must_create_for_pci_instance(device_identifier).leak_ref();
+            MUST(console.initialize_virtio_resources());
+            break;
+        }
+        case PCI::DeviceID::VirtIOEntropy: {
+            auto& rng = RNG::must_create_for_pci_instance(device_identifier).leak_ref();
+            MUST(rng.initialize_virtio_resources());
+            break;
+        }
+        case PCI::DeviceID::VirtIOGPU: {
+            // This should have been initialized by the graphics subsystem
+            break;
+        }
+        default:
+            dbgln_if(VIRTIO_DEBUG, "VirtIO: Unknown VirtIO device with ID: {}", device_identifier.hardware_id().device_id);
+            break;
+        }
+    }));
+}
+
+}

Kernel/Bus/VirtIO/Transport/PCIe/Detect.h

@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Kernel::VirtIO {
+
+void detect_pci_instances();
+
+}

Kernel/Bus/VirtIO/Transport/PCIe/InterruptHandler.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2021-2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Bus/VirtIO/Transport/PCIe/InterruptHandler.h>
+
+namespace Kernel::VirtIO {
+
+ErrorOr<NonnullOwnPtr<PCIeTransportInterruptHandler>> PCIeTransportInterruptHandler::create(PCIeTransportLink& transport_link, VirtIO::Device& parent_device, u8 irq)
+{
+    return TRY(adopt_nonnull_own_or_enomem(new (nothrow) PCIeTransportInterruptHandler(transport_link, parent_device, irq)));
+}
+
+PCIeTransportInterruptHandler::PCIeTransportInterruptHandler(PCIeTransportLink& transport_link, VirtIO::Device& parent_device, u8 irq)
+    : TransportInterruptHandler(parent_device)
+    , PCI::IRQHandler(transport_link, irq)
+{
+}
+
+bool PCIeTransportInterruptHandler::handle_irq(RegisterState const&)
+{
+    return notify_parent_device_on_interrupt();
+}
+
+}

Kernel/Bus/VirtIO/Transport/PCIe/InterruptHandler.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <Kernel/Bus/VirtIO/Device.h>
+#include <Kernel/Bus/VirtIO/Transport/InterruptHandler.h>
+#include <Kernel/Bus/VirtIO/Transport/PCIe/TransportLink.h>
+#include <Kernel/Interrupts/PCIIRQHandler.h>
+
+namespace Kernel::VirtIO {
+
+class PCIeTransportInterruptHandler final
+    : public TransportInterruptHandler
+    , public PCI::IRQHandler {
+public:
+    static ErrorOr<NonnullOwnPtr<PCIeTransportInterruptHandler>> create(PCIeTransportLink&, VirtIO::Device&, u8 irq);
+    virtual ~PCIeTransportInterruptHandler() override = default;
+
+    virtual StringView purpose() const override { return "VirtIO PCI IRQ Handler"sv; }
+
+private:
+    PCIeTransportInterruptHandler(PCIeTransportLink&, VirtIO::Device&, u8 irq);
+
+    //^ IRQHandler
+    virtual bool handle_irq(RegisterState const&) override;
+};
+}

Kernel/Bus/VirtIO/Transport/PCIe/TransportLink.cpp

@@ -0,0 +1,161 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Bus/PCI/API.h>
+#include <Kernel/Bus/PCI/IDs.h>
+#include <Kernel/Bus/VirtIO/Transport/PCIe/InterruptHandler.h>
+#include <Kernel/Bus/VirtIO/Transport/PCIe/TransportLink.h>
+
+namespace Kernel::VirtIO {
+
+ErrorOr<NonnullOwnPtr<TransportEntity>> PCIeTransportLink::create(PCI::DeviceIdentifier const& pci_identifier)
+{
+    return TRY(adopt_nonnull_own_or_enomem(new (nothrow) PCIeTransportLink(pci_identifier)));
+}
+
+StringView PCIeTransportLink::determine_device_class_name() const
+{
+    if (device_identifier().revision_id().value() == 0) {
+        // Note: If the device is a legacy (or transitional) device, therefore,
+        // probe the subsystem ID in the PCI header and figure out the
+        auto subsystem_device_id = device_identifier().subsystem_id().value();
+        switch (subsystem_device_id) {
+        case 1:
+            return "VirtIONetAdapter"sv;
+        case 2:
+            return "VirtIOBlockDevice"sv;
+        case 3:
+            return "VirtIOConsole"sv;
+        case 4:
+            return "VirtIORNG"sv;
+        default:
+            dbgln("VirtIO: Unknown subsystem_device_id {}", subsystem_device_id);
+            VERIFY_NOT_REACHED();
+        }
+    }
+
+    auto id = device_identifier().hardware_id();
+    VERIFY(id.vendor_id == PCI::VendorID::VirtIO);
+    switch (id.device_id) {
+    case PCI::DeviceID::VirtIONetAdapter:
+        return "VirtIONetAdapter"sv;
+    case PCI::DeviceID::VirtIOBlockDevice:
+        return "VirtIOBlockDevice"sv;
+    case PCI::DeviceID::VirtIOConsole:
+        return "VirtIOConsole"sv;
+    case PCI::DeviceID::VirtIOEntropy:
+        return "VirtIORNG"sv;
+    case PCI::DeviceID::VirtIOGPU:
+        return "VirtIOGPU"sv;
+    default:
+        dbgln("VirtIO: Unknown device_id {}", id.vendor_id);
+        VERIFY_NOT_REACHED();
+    }
+}
+
+ErrorOr<void> PCIeTransportLink::create_interrupt_handler(VirtIO::Device& parent_device)
+{
+    TRY(reserve_irqs(1, false));
+    auto irq = MUST(allocate_irq(0));
+    m_irq_handler = TRY(PCIeTransportInterruptHandler::create(*this, parent_device, irq));
+    return {};
+}
+
+PCIeTransportLink::PCIeTransportLink(PCI::DeviceIdentifier const& pci_identifier)
+    : PCI::Device(pci_identifier)
+{
+    dbgln("{}: Found @ {}", determine_device_class_name(), device_identifier().address());
+}
+
+ErrorOr<void> PCIeTransportLink::locate_configurations_and_resources(Badge<VirtIO::Device>, VirtIO::Device& parent_device)
+{
+    TRY(create_interrupt_handler(parent_device));
+    PCI::enable_bus_mastering(device_identifier());
+
+    auto capabilities = device_identifier().capabilities();
+    for (auto& capability : capabilities) {
+        if (capability.id().value() == PCI::Capabilities::ID::VendorSpecific) {
+            // We have a virtio_pci_cap
+            Configuration config {};
+            auto raw_config_type = capability.read8(0x3);
+            // NOTE: The VirtIO specification allows iteration of configurations
+            // through a special PCI capbility structure with the VIRTIO_PCI_CAP_PCI_CFG tag:
+            //
+            // "Each structure can be mapped by a Base Address register (BAR) belonging to the function, or accessed via
+            // the special VIRTIO_PCI_CAP_PCI_CFG field in the PCI configuration space"
+            //
+            // "The VIRTIO_PCI_CAP_PCI_CFG capability creates an alternative (and likely suboptimal) access method
+            // to the common configuration, notification, ISR and device-specific configuration regions."
+            //
+            // Also, it is *very* likely to see this PCI capability as the first vendor-specific capbility of a certain PCI function,
+            // but this is not guaranteed by the VirtIO specification.
+            // Therefore, ignore this type of configuration as this is not needed by our implementation currently.
+            if (raw_config_type == static_cast<u8>(ConfigurationType::PCICapabilitiesAccess))
+                continue;
+            if (raw_config_type < static_cast<u8>(ConfigurationType::Common) || raw_config_type > static_cast<u8>(ConfigurationType::PCICapabilitiesAccess)) {
+                dbgln("{}: Unknown capability configuration type: {}", device_name(), raw_config_type);
+                return Error::from_errno(ENXIO);
+            }
+            config.cfg_type = static_cast<ConfigurationType>(raw_config_type);
+            auto cap_length = capability.read8(0x2);
+            if (cap_length < 0x10) {
+                dbgln("{}: Unexpected capability size: {}", device_name(), cap_length);
+                break;
+            }
+            config.resource_index = capability.read8(0x4);
+            if (config.resource_index > 0x5) {
+                dbgln("{}: Unexpected capability BAR value: {}", device_name(), config.resource_index);
+                break;
+            }
+            config.offset = capability.read32(0x8);
+            config.length = capability.read32(0xc);
+            // NOTE: Configuration length of zero is an invalid configuration, or at the very least a configuration
+            // type we don't know how to handle correctly...
+            // The VIRTIO_PCI_CAP_PCI_CFG configuration structure has length of 0
+            // but because we ignore that type and all other types should have a length
+            // greater than 0, we should ignore any other configuration in case this condition is not met.
+            if (config.length == 0) {
+                dbgln("{}: Found configuration {}, with invalid length of 0", device_name(), (u32)config.cfg_type);
+                continue;
+            }
+            dbgln_if(VIRTIO_DEBUG, "{}: Found configuration {}, resource: {}, offset: {}, length: {}", device_name(), (u32)config.cfg_type, config.resource_index, config.offset, config.length);
+            if (config.cfg_type == ConfigurationType::Common)
+                m_use_mmio = true;
+            else if (config.cfg_type == ConfigurationType::Notify)
+                m_notify_multiplier = capability.read32(0x10);
+
+            m_configs.append(config);
+        }
+    }
+
+    if (m_use_mmio) {
+        for (auto& cfg : m_configs) {
+            auto mapping_io_window = TRY(IOWindow::create_for_pci_device_bar(device_identifier(), static_cast<PCI::HeaderType0BaseRegister>(cfg.resource_index)));
+            m_register_bases[cfg.resource_index] = move(mapping_io_window);
+        }
+        m_common_cfg = TRY(get_config(ConfigurationType::Common, 0));
+        m_notify_cfg = TRY(get_config(ConfigurationType::Notify, 0));
+        m_isr_cfg = TRY(get_config(ConfigurationType::ISR, 0));
+    } else {
+        auto mapping_io_window = TRY(IOWindow::create_for_pci_device_bar(device_identifier(), PCI::HeaderType0BaseRegister::BAR0));
+        m_register_bases[0] = move(mapping_io_window);
+    }
+    return {};
+}
+
+void PCIeTransportLink::disable_interrupts(Badge<VirtIO::Device>)
+{
+    disable_pin_based_interrupts();
+    m_irq_handler->disable_irq();
+}
+
+void PCIeTransportLink::enable_interrupts(Badge<VirtIO::Device>)
+{
+    m_irq_handler->enable_irq();
+    enable_pin_based_interrupts();
+}
+
+}

Kernel/Bus/VirtIO/Transport/PCIe/TransportLink.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+#include <Kernel/Bus/PCI/Device.h>
+#include <Kernel/Bus/VirtIO/Transport/Entity.h>
+#include <Kernel/Interrupts/PCIIRQHandler.h>
+
+namespace Kernel::VirtIO {
+
+class PCIeTransportLink final
+    : public TransportEntity
+    , public PCI::Device {
+public:
+    static ErrorOr<NonnullOwnPtr<TransportEntity>> create(PCI::DeviceIdentifier const& pci_identifier);
+
+    virtual StringView device_name() const override { return "VirtIOTransportLink"sv; }
+    virtual StringView determine_device_class_name() const override;
+
+private:
+    explicit PCIeTransportLink(PCI::DeviceIdentifier const& pci_identifier);
+
+    // ^TransportEntity
+    virtual ErrorOr<void> locate_configurations_and_resources(Badge<VirtIO::Device>, VirtIO::Device&) override;
+    virtual void disable_interrupts(Badge<VirtIO::Device>) override;
+    virtual void enable_interrupts(Badge<VirtIO::Device>) override;
+
+    ErrorOr<void> create_interrupt_handler(VirtIO::Device&);
+
+    // FIXME: There could be multiple IRQ (MSI-X) handlers for a VirtIO device.
+    // Find a way to use all of them.
+    OwnPtr<PCI::IRQHandler> m_irq_handler;
+};
+
+};