backends: Introduce HostIOMMUDevice abstract

A HostIOMMUDevice is an abstraction for an assigned device that is protected
by a physical IOMMU (aka host IOMMU). The userspace interaction with this
physical IOMMU can be done either through the VFIO IOMMU type 1 legacy
backend or the new iommufd backend. The assigned device can be a VFIO device
or a VDPA device. The HostIOMMUDevice is needed to interact with the host
IOMMU that protects the assigned device. It is especially useful when the
device is also protected by a virtual IOMMU as this latter use the translation
services of the physical IOMMU and is constrained by it. In that context the
HostIOMMUDevice can be passed to the virtual IOMMU to collect physical IOMMU
capabilities such as the supported address width. In the future, the virtual
IOMMU will use the HostIOMMUDevice to program the guest page tables in the
first translation stage of the physical IOMMU.

Introduce .realize() to initialize HostIOMMUDevice further after instance init.

Suggested-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

MAINTAINERS

@@ -2198,6 +2198,8 @@ M: Zhenzhong Duan <zhenzhong.duan@intel.com>
 S: Supported
 F: backends/iommufd.c
 F: include/sysemu/iommufd.h
+F: backends/host_iommu_device.c
+F: include/sysemu/host_iommu_device.h
 F: include/qemu/chardev_open.h
 F: util/chardev_open.c
 F: docs/devel/vfio-iommufd.rst

backends/host_iommu_device.c

@@ -0,0 +1,33 @@
+/*
+ * Host IOMMU device abstract
+ *
+ * Copyright (C) 2024 Intel Corporation.
+ *
+ * Authors: Zhenzhong Duan <zhenzhong.duan@intel.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "sysemu/host_iommu_device.h"
+
+OBJECT_DEFINE_ABSTRACT_TYPE(HostIOMMUDevice,
+                            host_iommu_device,
+                            HOST_IOMMU_DEVICE,
+                            OBJECT)
+
+static void host_iommu_device_class_init(ObjectClass *oc, void *data)
+{
+}
+
+static void host_iommu_device_init(Object *obj)
+{
+}
+
+static void host_iommu_device_finalize(Object *obj)
+{
+    HostIOMMUDevice *hiod = HOST_IOMMU_DEVICE(obj);
+
+    g_free(hiod->name);
+}

backends/meson.build

@@ -16,6 +16,7 @@ if host_os != 'windows'
 endif
 if host_os == 'linux'
   system_ss.add(files('hostmem-memfd.c'))
+  system_ss.add(files('host_iommu_device.c'))
 endif
 if keyutils.found()
     system_ss.add(keyutils, files('cryptodev-lkcf.c'))

include/sysemu/host_iommu_device.h

@@ -0,0 +1,53 @@
+/*
+ * Host IOMMU device abstract declaration
+ *
+ * Copyright (C) 2024 Intel Corporation.
+ *
+ * Authors: Zhenzhong Duan <zhenzhong.duan@intel.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ */
+
+#ifndef HOST_IOMMU_DEVICE_H
+#define HOST_IOMMU_DEVICE_H
+
+#include "qom/object.h"
+#include "qapi/error.h"
+
+#define TYPE_HOST_IOMMU_DEVICE "host-iommu-device"
+OBJECT_DECLARE_TYPE(HostIOMMUDevice, HostIOMMUDeviceClass, HOST_IOMMU_DEVICE)
+
+struct HostIOMMUDevice {
+    Object parent_obj;
+
+    char *name;
+};
+
+/**
+ * struct HostIOMMUDeviceClass - The base class for all host IOMMU devices.
+ *
+ * Different types of host devices (e.g., VFIO or VDPA device) or devices
+ * with different backend (e.g., VFIO legacy container or IOMMUFD backend)
+ * will have different implementations of the HostIOMMUDeviceClass.
+ */
+struct HostIOMMUDeviceClass {
+    ObjectClass parent_class;
+
+    /**
+     * @realize: initialize host IOMMU device instance further.
+     *
+     * Mandatory callback.
+     *
+     * @hiod: pointer to a host IOMMU device instance.
+     *
+     * @opaque: pointer to agent device of this host IOMMU device,
+     *          e.g., VFIO base device or VDPA device.
+     *
+     * @errp: pass an Error out when realize fails.
+     *
+     * Returns: true on success, false on failure.
+     */
+    bool (*realize)(HostIOMMUDevice *hiod, void *opaque, Error **errp);
+};
+#endif