hw/nitro: Add Nitro Vsock Bus

Add a dedicated bus for Nitro Enclave vsock devices. In Nitro Enclaves,
communication between parent and enclave/hypervisor happens almost
exclusively through vsock. The nitro-vsock-bus models this dependency
in QEMU, which allows devices in this bus to implement individual services
on top of vsock.

The nitro machine spawns this bus by creating the included
nitro-vsock-bridge sysbus device.

The nitro accel then advertises the Enclave's CID to the bus by calling
nitro_vsock_bridge_start_enclave() on the bridge device as soon as it
knows the CID.

Nitro vsock devices can listen to that event and learn the Enclave's CID
when it is available to perform actions, such as connect to the debug
serial vsock port.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alexander Graf <graf@amazon.com>
Link: https://lore.kernel.org/r/20260225220807.33092-4-graf@amazon.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

MAINTAINERS

@@ -3020,6 +3020,12 @@ F: hw/vmapple/*
 F: include/hw/vmapple/*
 F: docs/system/arm/vmapple.rst
 
+Nitro Enclaves (native)
+M: Alexander Graf <graf@amazon.com>
+S: Maintained
+F: hw/nitro/
+F: include/hw/nitro/
+
 Subsystems
 ----------
 Overall Audio backends

hw/Kconfig

@@ -22,6 +22,7 @@ source isa/Kconfig
 source mem/Kconfig
 source misc/Kconfig
 source net/Kconfig
+source nitro/Kconfig
 source nubus/Kconfig
 source nvme/Kconfig
 source nvram/Kconfig

hw/meson.build

@@ -44,6 +44,7 @@ subdir('isa')
 subdir('mem')
 subdir('misc')
 subdir('net')
+subdir('nitro')
 subdir('nubus')
 subdir('nvme')
 subdir('nvram')

hw/nitro/Kconfig

@@ -0,0 +1,2 @@
+config NITRO_VSOCK_BUS
+    bool

hw/nitro/meson.build

@@ -0,0 +1 @@
+system_ss.add(when: 'CONFIG_NITRO_VSOCK_BUS', if_true: files('nitro-vsock-bus.c'))

hw/nitro/nitro-vsock-bus.c

@@ -0,0 +1,98 @@
+/*
+ * Nitro Enclave Vsock Bus
+ *
+ * Copyright © 2026 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Authors:
+ *   Alexander Graf <graf@amazon.com>
+ *
+ * A bus for Nitro Enclave vsock devices. In Nitro Enclaves, communication
+ * between parent and enclave/hypervisor happens almost exclusively through
+ * vsock. The nitro-vsock-bus models this dependency in QEMU, which allows
+ * devices in this bus to implement individual services on top of vsock.
+ *
+ * The nitro accel advertises the Enclave's CID to the bus by calling
+ * nitro_vsock_bridge_start_enclave() on the bridge device as soon as it
+ * knows the CID.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "monitor/qdev.h"
+#include "hw/core/sysbus.h"
+#include "hw/nitro/nitro-vsock-bus.h"
+
+void nitro_vsock_bridge_start_enclave(NitroVsockBridge *bridge,
+                                      uint32_t enclave_cid, Error **errp)
+{
+    ERRP_GUARD();
+    BusState *qbus = BUS(&bridge->bus);
+    BusChild *kid;
+
+    bridge->enclave_cid = enclave_cid;
+
+    QTAILQ_FOREACH(kid, &qbus->children, sibling) {
+        NitroVsockDevice *ndev = NITRO_VSOCK_DEVICE(kid->child);
+        NitroVsockDeviceClass *ndc = NITRO_VSOCK_DEVICE_GET_CLASS(ndev);
+
+        if (ndc->enclave_started) {
+            ndc->enclave_started(ndev, enclave_cid, errp);
+            if (*errp) {
+                return;
+            }
+        }
+    }
+}
+
+NitroVsockBridge *nitro_vsock_bridge_create(void)
+{
+    DeviceState *dev = qdev_new(TYPE_NITRO_VSOCK_BRIDGE);
+
+    qdev_set_id(dev, g_strdup("nitro-vsock"), &error_fatal);
+    sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
+
+    return NITRO_VSOCK_BRIDGE(dev);
+}
+
+static void nitro_vsock_bridge_init(Object *obj)
+{
+    NitroVsockBridge *s = NITRO_VSOCK_BRIDGE(obj);
+
+    qbus_init(&s->bus, sizeof(s->bus), TYPE_NITRO_VSOCK_BUS,
+              DEVICE(s), "nitro-vsock");
+    object_property_add_uint32_ptr(obj, "enclave-cid",
+                                   &s->enclave_cid, OBJ_PROP_FLAG_READ);
+}
+
+static void nitro_vsock_device_class_init(ObjectClass *oc, const void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(oc);
+
+    dc->bus_type = TYPE_NITRO_VSOCK_BUS;
+}
+
+static const TypeInfo nitro_vsock_bus_types[] = {
+    {
+        .name = TYPE_NITRO_VSOCK_BUS,
+        .parent = TYPE_BUS,
+        .instance_size = sizeof(NitroVsockBus),
+    },
+    {
+        .name = TYPE_NITRO_VSOCK_BRIDGE,
+        .parent = TYPE_SYS_BUS_DEVICE,
+        .instance_size = sizeof(NitroVsockBridge),
+        .instance_init = nitro_vsock_bridge_init,
+    },
+    {
+        .name = TYPE_NITRO_VSOCK_DEVICE,
+        .parent = TYPE_DEVICE,
+        .instance_size = sizeof(NitroVsockDevice),
+        .class_size = sizeof(NitroVsockDeviceClass),
+        .class_init = nitro_vsock_device_class_init,
+        .abstract = true,
+    },
+};
+
+DEFINE_TYPES(nitro_vsock_bus_types);

hw/nitro/trace-events

@@ -0,0 +1,2 @@
+# See docs/devel/tracing.rst for syntax documentation.
+

hw/nitro/trace.h

@@ -0,0 +1,4 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include "trace/trace-hw_nitro.h"

include/hw/nitro/nitro-vsock-bus.h

@@ -0,0 +1,71 @@
+/*
+ * Nitro Enclave Vsock Bus
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef HW_NITRO_VSOCK_BUS_H
+#define HW_NITRO_VSOCK_BUS_H
+
+#include "hw/core/qdev.h"
+#include "hw/core/sysbus.h"
+#include "qom/object.h"
+
+#define TYPE_NITRO_VSOCK_BUS "nitro-vsock-bus"
+OBJECT_DECLARE_SIMPLE_TYPE(NitroVsockBus, NITRO_VSOCK_BUS)
+
+#define TYPE_NITRO_VSOCK_BRIDGE "nitro-vsock-bridge"
+OBJECT_DECLARE_SIMPLE_TYPE(NitroVsockBridge, NITRO_VSOCK_BRIDGE)
+
+#define TYPE_NITRO_VSOCK_DEVICE "nitro-vsock-device"
+OBJECT_DECLARE_TYPE(NitroVsockDevice, NitroVsockDeviceClass,
+                    NITRO_VSOCK_DEVICE)
+
+struct NitroVsockBus {
+    BusState parent_obj;
+};
+
+struct NitroVsockBridge {
+    SysBusDevice parent_obj;
+
+    NitroVsockBus bus;
+    uint32_t enclave_cid;
+};
+
+struct NitroVsockDevice {
+    DeviceState parent_obj;
+};
+
+struct NitroVsockDeviceClass {
+    DeviceClass parent_class;
+
+    /*
+     * Called after the enclave has been started and the CID is known.
+     * Devices use this to establish vsock connections to the enclave.
+     */
+    void (*enclave_started)(NitroVsockDevice *dev, uint32_t enclave_cid,
+                            Error **errp);
+};
+
+/*
+ * Machine helper to create the Nitro vsock bridge sysbus device.
+ */
+NitroVsockBridge *nitro_vsock_bridge_create(void);
+
+/*
+ * Find the Nitro vsock bridge on the sysbus.
+ */
+static inline NitroVsockBridge *nitro_vsock_bridge_find(void)
+{
+    return NITRO_VSOCK_BRIDGE(
+        object_resolve_path_type("", TYPE_NITRO_VSOCK_BRIDGE, NULL));
+}
+
+/*
+ * Notify the bridge that the enclave has started. Dispatches
+ * enclave_started() to all devices on the bus.
+ */
+void nitro_vsock_bridge_start_enclave(NitroVsockBridge *bridge,
+                                      uint32_t enclave_cid, Error **errp);
+
+#endif /* HW_NITRO_VSOCK_BUS_H */

meson.build

@@ -3620,6 +3620,7 @@ if have_system
     'hw/misc/macio',
     'hw/net',
     'hw/net/can',
+    'hw/nitro',
     'hw/nubus',
     'hw/nvme',
     'hw/nvram',