Linux Virtualization - Nov 2019 - [PATCH V11 6/6] docs: sample driver to demonstrate how to implement virtio-mdev framework

Hi all:

There are hardwares that can do virtio datapath offloading while
having its own control path. This path tries to implement a mdev based
unified API to support using kernel virtio driver to drive those
devices. This is done by introducing a new mdev transport for virtio
(virtio_mdev) and register itself as a new kind of mdev driver. Then
it provides a unified way for kernel virtio driver to talk with mdev
device implementation.

Though the series only contains kernel driver support, the goal is to
make the transport generic enough to support userspace drivers. This
means vhost-mdev[1] could be built on top as well by resuing the
transport.

A sample driver is also implemented which simulate a virito-net
loopback ethernet device on top of vringh + workqueue. This could be
used as a reference implementation for real hardware driver.

Also a real IFC VF driver was also posted here[2] which is a good
reference for vendors who is interested in their own virtio datapath
offloading product.

Consider mdev framework only support VFIO device and driver right now,
this series also extend it to support other types. This is done
through introducing class id to the device and pairing it with
id_talbe claimed by the driver. On top, this seris also decouple
device specific ops out of the common ones for implementing class
specific operations over mdev bus.

Pktgen test was done with virito-net + mvnet loop back device.

Please review.

[1] https://lkml.org/lkml/2019/11/5/424
[2] https://lkml.org/lkml/2019/11/5/227

Changes from V10:
- rename mvnet to mvnet_loopback
- fix typo in the help text for sample Kconfig

Changes from V9:
- Tweak the help text for virito-mdev kconfig

Changes from V8:
- try silent checkpatch, some are still there becuase they were inherited
  from virtio_config_ops which needs to be resolved in an independent series
- tweak on the comment and doc
- remove VIRTIO_MDEV_F_VERSION_1 completely
- rename CONFIG_VIRTIO_MDEV_DEVICE to CONFIG_VIRTIO_MDEV

Changes from V7:
- drop {set|get}_mdev_features for virtio
- typo and comment style fixes

Changes from V6:
- rename ops files and compile guard

Changes from V5:
- use dev_warn() instead of WARN(1) when class id is not set
- validate id_table before trying to do matching between device and
  driver
- add wildcard for modpost script
- use unique name for id_table
- move get_mdev_features() to be the first member of virtio_device_ops
  and more comments for it
- typo fixes for the comments above virtio_mdev_ops

Changes from V4:
- keep mdev_set_class() for the device that doesn't use device ops
- use union for device ops pointer in mdev_device
- introduce class specific helper for getting is device ops
- use WARN_ON instead of BUG_ON in mdev_set_virtio_ops
- explain details of get_mdev_features() and get_vendor_id()
- distinguish the optional virito device ops from mandatory ones and
  make get_generation() optional
- rename vfio_mdev.h to vfio_mdev_ops.h, rename virito_mdev.h to
  virtio_mdev_ops.h
- don't abuse version fileds in virtio_mdev structure, use features
  instead
- fix warning during device remove
- style & docs tweaks and typo fixes

Changes from V3:
- document that class id (device ops) must be specified in create()
- add WARN() when trying to set class_id when it has already set
- add WARN() when class_id is not specified in create() and correctly
  return an error in this case
- correct the prototype of mdev_set_class() in the doc
- add documention of mdev_set_class()
- remove the unnecessary "class_id_fail" label when class id is not
  specified in create()
- convert id_table in vfio_mdev to const
- move mdev_set_class and its friends after mdev_uuid()
- suqash the patch of bus uevent into patch of introducing class id
- tweak the words in the docs per Cornelia suggestion
- tie class_id and device ops through class specific initialization
  routine like mdev_set_vfio_ops()
- typos fixes in the docs of virtio-mdev callbacks
- document the usage of virtqueues in struct virtio_mdev_device
- remove the useless vqs array in struct virtio_mdev_device
- rename MDEV_ID_XXX to MDEV_CLASS_ID_XXX

Changes from V2:
- fail when class_id is not specified
- drop the vringh patch
- match the doc to the code
- tweak the commit log
- move device_ops from parent to mdev device
- remove the unused MDEV_ID_VHOST

Changes from V1:
- move virtio_mdev.c to drivers/virtio
- store class_id in mdev_device instead of mdev_parent
- store device_ops in mdev_device instead of mdev_parent
- reorder the patch, vringh fix comes first
- really silent compiling warnings
- really switch to use u16 for class_id
- uevent and modpost support for mdev class_id
- vraious tweaks per comments from Parav

Changes from RFC-V2:
- silent compile warnings on some specific configuration
- use u16 instead u8 for class id
- reseve MDEV_ID_VHOST for future vhost-mdev work
- introduce "virtio" type for mvnet and make "vhost" type
for future
  work
- add entries in MAINTAINER
- tweak and typos fixes in commit log

Changes from RFC-V1:
- rename device id to class id
- add docs for class id and device specific ops (device_ops)
- split device_ops into seperate headers
- drop the mdev_set_dma_ops()
- use device_ops to implement the transport API, then it's not a part
  of UAPI any more
- use GFP_ATOMIC in mvnet sample device and other tweaks
- set_vring_base/get_vring_base support for mvnet device

Jason Wang (6):
  mdev: class id support
  modpost: add support for mdev class id
  mdev: introduce device specific ops
  mdev: introduce virtio device and its device ops
  virtio: introduce a mdev based transport
  docs: sample driver to demonstrate how to implement virtio-mdev
    framework

 .../driver-api/vfio-mediated-device.rst       |  38 +-
 MAINTAINERS                                   |   3 +
 drivers/gpu/drm/i915/gvt/kvmgt.c              |  17 +-
 drivers/s390/cio/vfio_ccw_ops.c               |  17 +-
 drivers/s390/crypto/vfio_ap_ops.c             |  13 +-
 drivers/vfio/mdev/mdev_core.c                 |  60 ++
 drivers/vfio/mdev/mdev_driver.c               |  25 +
 drivers/vfio/mdev/mdev_private.h              |   8 +
 drivers/vfio/mdev/vfio_mdev.c                 |  45 +-
 drivers/virtio/Kconfig                        |  13 +
 drivers/virtio/Makefile                       |   1 +
 drivers/virtio/virtio_mdev.c                  | 406 +++++++++++
 include/linux/mdev.h                          |  57 +-
 include/linux/mdev_vfio_ops.h                 |  52 ++
 include/linux/mdev_virtio_ops.h               | 147 ++++
 include/linux/mod_devicetable.h               |   8 +
 samples/Kconfig                               |  10 +
 samples/vfio-mdev/Makefile                    |   1 +
 samples/vfio-mdev/mbochs.c                    |  19 +-
 samples/vfio-mdev/mdpy.c                      |  19 +-
 samples/vfio-mdev/mtty.c                      |  17 +-
 samples/vfio-mdev/mvnet_loopback.c            | 687 ++++++++++++++++++
 scripts/mod/devicetable-offsets.c             |   3 +
 scripts/mod/file2alias.c                      |  11 +
 24 files changed, 1586 insertions(+), 91 deletions(-)
 create mode 100644 drivers/virtio/virtio_mdev.c
 create mode 100644 include/linux/mdev_vfio_ops.h
 create mode 100644 include/linux/mdev_virtio_ops.h
 create mode 100644 samples/vfio-mdev/mvnet_loopback.c

-- 
2.19.1

Mdev bus only supports vfio driver right now, so it doesn't implement
match method. But in the future, we may add drivers other than vfio,
the first driver could be virtio-mdev. This means we need to add
device class id support in bus match method to pair the mdev device
and mdev driver correctly.

So this patch adds id_table to mdev_driver and class_id for mdev
device with the match method for mdev bus.

Reviewed-by: Parav Pandit <parav at mellanox.com>
Reviewed-by: Cornelia Huck <cohuck at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 .../driver-api/vfio-mediated-device.rst       |  5 ++++
 drivers/gpu/drm/i915/gvt/kvmgt.c              |  1 +
 drivers/s390/cio/vfio_ccw_ops.c               |  1 +
 drivers/s390/crypto/vfio_ap_ops.c             |  1 +
 drivers/vfio/mdev/mdev_core.c                 | 17 +++++++++++++
 drivers/vfio/mdev/mdev_driver.c               | 25 +++++++++++++++++++
 drivers/vfio/mdev/mdev_private.h              |  1 +
 drivers/vfio/mdev/vfio_mdev.c                 |  6 +++++
 include/linux/mdev.h                          |  8 ++++++
 include/linux/mod_devicetable.h               |  8 ++++++
 samples/vfio-mdev/mbochs.c                    |  1 +
 samples/vfio-mdev/mdpy.c                      |  1 +
 samples/vfio-mdev/mtty.c                      |  1 +
 13 files changed, 76 insertions(+)

diff --git a/Documentation/driver-api/vfio-mediated-device.rst
b/Documentation/driver-api/vfio-mediated-device.rst
index 25eb7d5b834b..6709413bee29 100644
--- a/Documentation/driver-api/vfio-mediated-device.rst
+++ b/Documentation/driver-api/vfio-mediated-device.rst
@@ -102,12 +102,14 @@ structure to represent a mediated device's driver::
       * @probe: called when new device created
       * @remove: called when device removed
       * @driver: device driver structure
+      * @id_table: the ids serviced by this driver
       */
      struct mdev_driver {
 	     const char *name;
 	     int  (*probe)  (struct device *dev);
 	     void (*remove) (struct device *dev);
 	     struct device_driver    driver;
+	     const struct mdev_class_id *id_table;
      };
 
 A mediated bus driver for mdev should use this structure in the function calls
@@ -170,6 +172,9 @@ that a driver should use to unregister itself with the mdev
core driver::
 
 	extern void mdev_unregister_device(struct device *dev);
 
+It is also required to specify the class_id in create() callback through::
+
+	int mdev_set_class(struct mdev_device *mdev, u16 id);
 
 Mediated Device Management Interface Through sysfs
 =================================================diff --git
a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index 343d79c1cb7e..6420f0dbd31b 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -678,6 +678,7 @@ static int intel_vgpu_create(struct kobject *kobj, struct
mdev_device *mdev)
 		     dev_name(mdev_dev(mdev)));
 	ret = 0;
 
+	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
 out:
 	return ret;
 }
diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index f0d71ab77c50..cf2c013ae32f 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -129,6 +129,7 @@ static int vfio_ccw_mdev_create(struct kobject *kobj, struct
mdev_device *mdev)
 			   private->sch->schid.ssid,
 			   private->sch->schid.sch_no);
 
+	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
 	return 0;
 }
 
diff --git a/drivers/s390/crypto/vfio_ap_ops.c
b/drivers/s390/crypto/vfio_ap_ops.c
index 5c0f53c6dde7..07c31070afeb 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -343,6 +343,7 @@ static int vfio_ap_mdev_create(struct kobject *kobj, struct
mdev_device *mdev)
 	list_add(&matrix_mdev->node, &matrix_dev->mdev_list);
 	mutex_unlock(&matrix_dev->lock);
 
+	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
 	return 0;
 }
 
diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
index b558d4cfd082..7bfa2e46e829 100644
--- a/drivers/vfio/mdev/mdev_core.c
+++ b/drivers/vfio/mdev/mdev_core.c
@@ -45,6 +45,17 @@ void mdev_set_drvdata(struct mdev_device *mdev, void *data)
 }
 EXPORT_SYMBOL(mdev_set_drvdata);
 
+/*
+ * Specify the class for the mdev device, this must be called during
+ * create() callback.
+ */
+void mdev_set_class(struct mdev_device *mdev, u16 id)
+{
+	WARN_ON(mdev->class_id);
+	mdev->class_id = id;
+}
+EXPORT_SYMBOL(mdev_set_class);
+
 struct device *mdev_dev(struct mdev_device *mdev)
 {
 	return &mdev->dev;
@@ -324,6 +335,12 @@ int mdev_device_create(struct kobject *kobj,
 	if (ret)
 		goto ops_create_fail;
 
+	if (!mdev->class_id) {
+		ret = -EINVAL;
+		dev_warn(dev, "mdev vendor driver failed to specify device
class\n");
+		goto add_fail;
+	}
+
 	ret = device_add(&mdev->dev);
 	if (ret)
 		goto add_fail;
diff --git a/drivers/vfio/mdev/mdev_driver.c b/drivers/vfio/mdev/mdev_driver.c
index 0d3223aee20b..ed06433693e8 100644
--- a/drivers/vfio/mdev/mdev_driver.c
+++ b/drivers/vfio/mdev/mdev_driver.c
@@ -69,8 +69,33 @@ static int mdev_remove(struct device *dev)
 	return 0;
 }
 
+static int mdev_match(struct device *dev, struct device_driver *drv)
+{
+	unsigned int i;
+	struct mdev_device *mdev = to_mdev_device(dev);
+	struct mdev_driver *mdrv = to_mdev_driver(drv);
+	const struct mdev_class_id *ids = mdrv->id_table;
+
+	if (!ids)
+		return 0;
+
+	for (i = 0; ids[i].id; i++)
+		if (ids[i].id == mdev->class_id)
+			return 1;
+	return 0;
+}
+
+static int mdev_uevent(struct device *dev, struct kobj_uevent_env *env)
+{
+	struct mdev_device *mdev = to_mdev_device(dev);
+
+	return add_uevent_var(env, "MODALIAS=mdev:c%02X",
mdev->class_id);
+}
+
 struct bus_type mdev_bus_type = {
 	.name		= "mdev",
+	.match		= mdev_match,
+	.uevent		= mdev_uevent,
 	.probe		= mdev_probe,
 	.remove		= mdev_remove,
 };
diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
index 7d922950caaf..c65f436c1869 100644
--- a/drivers/vfio/mdev/mdev_private.h
+++ b/drivers/vfio/mdev/mdev_private.h
@@ -33,6 +33,7 @@ struct mdev_device {
 	struct kobject *type_kobj;
 	struct device *iommu_device;
 	bool active;
+	u16 class_id;
 };
 
 #define to_mdev_device(dev)	container_of(dev, struct mdev_device, dev)
diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c
index 30964a4e0a28..38431e9ef7f5 100644
--- a/drivers/vfio/mdev/vfio_mdev.c
+++ b/drivers/vfio/mdev/vfio_mdev.c
@@ -120,10 +120,16 @@ static void vfio_mdev_remove(struct device *dev)
 	vfio_del_group_dev(dev);
 }
 
+static const struct mdev_class_id vfio_id_table[] = {
+	{ MDEV_CLASS_ID_VFIO },
+	{ 0 },
+};
+
 static struct mdev_driver vfio_mdev_driver = {
 	.name	= "vfio_mdev",
 	.probe	= vfio_mdev_probe,
 	.remove	= vfio_mdev_remove,
+	.id_table = vfio_id_table,
 };
 
 static int __init vfio_mdev_init(void)
diff --git a/include/linux/mdev.h b/include/linux/mdev.h
index 0ce30ca78db0..78b69d09eb54 100644
--- a/include/linux/mdev.h
+++ b/include/linux/mdev.h
@@ -118,6 +118,7 @@ struct mdev_type_attribute mdev_type_attr_##_name =		\
  * @probe: called when new device created
  * @remove: called when device removed
  * @driver: device driver structure
+ * @id_table: the ids serviced by this driver
  *
  **/
 struct mdev_driver {
@@ -125,6 +126,7 @@ struct mdev_driver {
 	int  (*probe)(struct device *dev);
 	void (*remove)(struct device *dev);
 	struct device_driver driver;
+	const struct mdev_class_id *id_table;
 };
 
 #define to_mdev_driver(drv)	container_of(drv, struct mdev_driver, driver)
@@ -132,6 +134,7 @@ struct mdev_driver {
 void *mdev_get_drvdata(struct mdev_device *mdev);
 void mdev_set_drvdata(struct mdev_device *mdev, void *data);
 const guid_t *mdev_uuid(struct mdev_device *mdev);
+void mdev_set_class(struct mdev_device *mdev, u16 id);
 
 extern struct bus_type mdev_bus_type;
 
@@ -145,4 +148,9 @@ struct device *mdev_parent_dev(struct mdev_device *mdev);
 struct device *mdev_dev(struct mdev_device *mdev);
 struct mdev_device *mdev_from_dev(struct device *dev);
 
+enum {
+	MDEV_CLASS_ID_VFIO = 1,
+	/* New entries must be added here */
+};
+
 #endif /* MDEV_H */
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 5714fd35a83c..f32c6e44fb1a 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -821,4 +821,12 @@ struct wmi_device_id {
 	const void *context;
 };
 
+/**
+ * struct mdev_class_id - MDEV device class identifier
+ * @id: Used to identify a specific class of device, e.g vfio-mdev device.
+ */
+struct mdev_class_id {
+	__u16 id;
+};
+
 #endif /* LINUX_MOD_DEVICETABLE_H */
diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
index ac5c8c17b1ff..115bc5074656 100644
--- a/samples/vfio-mdev/mbochs.c
+++ b/samples/vfio-mdev/mbochs.c
@@ -561,6 +561,7 @@ static int mbochs_create(struct kobject *kobj, struct
mdev_device *mdev)
 	mbochs_reset(mdev);
 
 	mbochs_used_mbytes += type->mbytes;
+	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
 	return 0;
 
 err_mem:
diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c
index cc86bf6566e4..665614574d50 100644
--- a/samples/vfio-mdev/mdpy.c
+++ b/samples/vfio-mdev/mdpy.c
@@ -269,6 +269,7 @@ static int mdpy_create(struct kobject *kobj, struct
mdev_device *mdev)
 	mdpy_reset(mdev);
 
 	mdpy_count++;
+	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
 	return 0;
 }
 
diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
index ce84a300a4da..90da12ff7fd9 100644
--- a/samples/vfio-mdev/mtty.c
+++ b/samples/vfio-mdev/mtty.c
@@ -755,6 +755,7 @@ static int mtty_create(struct kobject *kobj, struct
mdev_device *mdev)
 	list_add(&mdev_state->next, &mdev_devices_list);
 	mutex_unlock(&mdev_list_lock);
 
+	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
 	return 0;
 }
 
-- 
2.19.1

Add support to parse mdev class id table.

Reviewed-by: Parav Pandit <parav at mellanox.com>
Reviewed-by: Cornelia Huck <cohuck at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/vfio/mdev/vfio_mdev.c     |  2 ++
 scripts/mod/devicetable-offsets.c |  3 +++
 scripts/mod/file2alias.c          | 11 +++++++++++
 3 files changed, 16 insertions(+)

diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c
index 38431e9ef7f5..a6641cd8b5a3 100644
--- a/drivers/vfio/mdev/vfio_mdev.c
+++ b/drivers/vfio/mdev/vfio_mdev.c
@@ -125,6 +125,8 @@ static const struct mdev_class_id vfio_id_table[] = {
 	{ 0 },
 };
 
+MODULE_DEVICE_TABLE(mdev, vfio_id_table);
+
 static struct mdev_driver vfio_mdev_driver = {
 	.name	= "vfio_mdev",
 	.probe	= vfio_mdev_probe,
diff --git a/scripts/mod/devicetable-offsets.c
b/scripts/mod/devicetable-offsets.c
index 054405b90ba4..6cbb1062488a 100644
--- a/scripts/mod/devicetable-offsets.c
+++ b/scripts/mod/devicetable-offsets.c
@@ -231,5 +231,8 @@ int main(void)
 	DEVID(wmi_device_id);
 	DEVID_FIELD(wmi_device_id, guid_string);
 
+	DEVID(mdev_class_id);
+	DEVID_FIELD(mdev_class_id, id);
+
 	return 0;
 }
diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index c91eba751804..45f1c22f49be 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -1335,6 +1335,16 @@ static int do_wmi_entry(const char *filename, void
*symval, char *alias)
 	return 1;
 }
 
+/* looks like: "mdev:cN" */
+static int do_mdev_entry(const char *filename, void *symval, char *alias)
+{
+	DEF_FIELD(symval, mdev_class_id, id);
+
+	sprintf(alias, "mdev:c%02X", id);
+	add_wildcard(alias);
+	return 1;
+}
+
 /* Does namelen bytes of name exactly match the symbol? */
 static bool sym_is(const char *name, unsigned namelen, const char *symbol)
 {
@@ -1407,6 +1417,7 @@ static const struct devtable devtable[] = {
 	{"typec", SIZE_typec_device_id, do_typec_entry},
 	{"tee", SIZE_tee_client_device_id, do_tee_entry},
 	{"wmi", SIZE_wmi_device_id, do_wmi_entry},
+	{"mdev", SIZE_mdev_class_id, do_mdev_entry},
 };
 
 /* Create MODULE_ALIAS() statements.
-- 
2.19.1

Currently, except for the create and remove, the rest of
mdev_parent_ops is designed for vfio-mdev driver only and may not help
for kernel mdev driver. With the help of class id, this patch
introduces device specific callbacks inside mdev_device
structure. This allows different set of callback to be used by
vfio-mdev and virtio-mdev.

Reviewed-by: Parav Pandit <parav at mellanox.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 .../driver-api/vfio-mediated-device.rst       | 35 +++++++++----
 MAINTAINERS                                   |  1 +
 drivers/gpu/drm/i915/gvt/kvmgt.c              | 18 ++++---
 drivers/s390/cio/vfio_ccw_ops.c               | 18 ++++---
 drivers/s390/crypto/vfio_ap_ops.c             | 14 +++--
 drivers/vfio/mdev/mdev_core.c                 | 24 ++++++++-
 drivers/vfio/mdev/mdev_private.h              |  5 ++
 drivers/vfio/mdev/vfio_mdev.c                 | 37 ++++++-------
 include/linux/mdev.h                          | 43 ++++-----------
 include/linux/mdev_vfio_ops.h                 | 52 +++++++++++++++++++
 samples/vfio-mdev/mbochs.c                    | 20 ++++---
 samples/vfio-mdev/mdpy.c                      | 20 ++++---
 samples/vfio-mdev/mtty.c                      | 18 ++++---
 13 files changed, 206 insertions(+), 99 deletions(-)
 create mode 100644 include/linux/mdev_vfio_ops.h

diff --git a/Documentation/driver-api/vfio-mediated-device.rst
b/Documentation/driver-api/vfio-mediated-device.rst
index 6709413bee29..04d56884c357 100644
--- a/Documentation/driver-api/vfio-mediated-device.rst
+++ b/Documentation/driver-api/vfio-mediated-device.rst
@@ -152,15 +152,6 @@ callbacks per mdev parent device, per mdev type, or any
other categorization.
 Vendor drivers are expected to be fully asynchronous in this respect or
 provide their own internal resource protection.)
 
-The callbacks in the mdev_parent_ops structure are as follows:
-
-* open: open callback of mediated device
-* close: close callback of mediated device
-* ioctl: ioctl callback of mediated device
-* read : read emulation callback
-* write: write emulation callback
-* mmap: mmap emulation callback
-
 A driver should use the mdev_parent_ops structure in the function call to
 register itself with the mdev core driver::
 
@@ -172,10 +163,34 @@ that a driver should use to unregister itself with the
mdev core driver::
 
 	extern void mdev_unregister_device(struct device *dev);
 
-It is also required to specify the class_id in create() callback through::
+As multiple types of mediated devices may be supported, class id needs
+to be specified in the create() callback. This could be done
+explicitly for the device that interacts with the mdev device directly
+through::
 
 	int mdev_set_class(struct mdev_device *mdev, u16 id);
 
+For the device that uses the mdev bus for its operation, the class
+should provide helper function to set class id and device specific
+ops. E.g for vfio-mdev devices, the function to be called is::
+
+	int mdev_set_vfio_ops(struct mdev_device *mdev,
+                              const struct mdev_vfio_device_ops *vfio_ops);
+
+The class id (set by this function to MDEV_CLASS_ID_VFIO) is used to
+match a device with an mdev driver via its id table. The device
+specific callbacks (specified in *vfio_ops) are obtainable via
+mdev_get_vfio_ops() (for use by the mdev bus driver). A vfio-mdev
+device (class id MDEV_CLASS_ID_VFIO) uses the following
+device-specific ops:
+
+* open: open callback of vfio mediated device
+* close: close callback of vfio mediated device
+* ioctl: ioctl callback of vfio mediated device
+* read : read emulation callback
+* write: write emulation callback
+* mmap: mmap emulation callback
+
 Mediated Device Management Interface Through sysfs
 ================================================= 
diff --git a/MAINTAINERS b/MAINTAINERS
index cba1095547fd..f661d13344d6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17121,6 +17121,7 @@ S:	Maintained
 F:	Documentation/driver-api/vfio-mediated-device.rst
 F:	drivers/vfio/mdev/
 F:	include/linux/mdev.h
+F:	include/linux/mdev_vfio_ops.h
 F:	samples/vfio-mdev/
 
 VFIO PLATFORM DRIVER
diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index 6420f0dbd31b..662f3a672372 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -42,6 +42,7 @@
 #include <linux/kvm_host.h>
 #include <linux/vfio.h>
 #include <linux/mdev.h>
+#include <linux/mdev_vfio_ops.h>
 #include <linux/debugfs.h>
 
 #include <linux/nospec.h>
@@ -643,6 +644,8 @@ static void kvmgt_put_vfio_device(void *vgpu)
 	vfio_device_put(((struct intel_vgpu *)vgpu)->vdev.vfio_device);
 }
 
+static const struct mdev_vfio_device_ops intel_vfio_vgpu_dev_ops;
+
 static int intel_vgpu_create(struct kobject *kobj, struct mdev_device *mdev)
 {
 	struct intel_vgpu *vgpu = NULL;
@@ -678,7 +681,7 @@ static int intel_vgpu_create(struct kobject *kobj, struct
mdev_device *mdev)
 		     dev_name(mdev_dev(mdev)));
 	ret = 0;
 
-	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
+	mdev_set_vfio_ops(mdev, &intel_vfio_vgpu_dev_ops);
 out:
 	return ret;
 }
@@ -1599,20 +1602,21 @@ static const struct attribute_group *intel_vgpu_groups[]
= {
 	NULL,
 };
 
-static struct mdev_parent_ops intel_vgpu_ops = {
-	.mdev_attr_groups       = intel_vgpu_groups,
-	.create			= intel_vgpu_create,
-	.remove			= intel_vgpu_remove,
-
+static const struct mdev_vfio_device_ops intel_vfio_vgpu_dev_ops = {
 	.open			= intel_vgpu_open,
 	.release		= intel_vgpu_release,
-
 	.read			= intel_vgpu_read,
 	.write			= intel_vgpu_write,
 	.mmap			= intel_vgpu_mmap,
 	.ioctl			= intel_vgpu_ioctl,
 };
 
+static struct mdev_parent_ops intel_vgpu_ops = {
+	.mdev_attr_groups       = intel_vgpu_groups,
+	.create			= intel_vgpu_create,
+	.remove			= intel_vgpu_remove,
+};
+
 static int kvmgt_host_init(struct device *dev, void *gvt, const void *ops)
 {
 	struct attribute **kvm_type_attrs;
diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index cf2c013ae32f..fa473ded71c7 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -12,6 +12,7 @@
 
 #include <linux/vfio.h>
 #include <linux/mdev.h>
+#include <linux/mdev_vfio_ops.h>
 #include <linux/nospec.h>
 #include <linux/slab.h>
 
@@ -110,6 +111,8 @@ static struct attribute_group *mdev_type_groups[] = {
 	NULL,
 };
 
+static const struct mdev_vfio_device_ops mdev_vfio_ops;
+
 static int vfio_ccw_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
 {
 	struct vfio_ccw_private *private @@ -129,7 +132,7 @@ static int
vfio_ccw_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
 			   private->sch->schid.ssid,
 			   private->sch->schid.sch_no);
 
-	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
+	mdev_set_vfio_ops(mdev, &mdev_vfio_ops);
 	return 0;
 }
 
@@ -575,11 +578,7 @@ static ssize_t vfio_ccw_mdev_ioctl(struct mdev_device
*mdev,
 	}
 }
 
-static const struct mdev_parent_ops vfio_ccw_mdev_ops = {
-	.owner			= THIS_MODULE,
-	.supported_type_groups  = mdev_type_groups,
-	.create			= vfio_ccw_mdev_create,
-	.remove			= vfio_ccw_mdev_remove,
+static const struct mdev_vfio_device_ops mdev_vfio_ops = {
 	.open			= vfio_ccw_mdev_open,
 	.release		= vfio_ccw_mdev_release,
 	.read			= vfio_ccw_mdev_read,
@@ -587,6 +586,13 @@ static const struct mdev_parent_ops vfio_ccw_mdev_ops = {
 	.ioctl			= vfio_ccw_mdev_ioctl,
 };
 
+static const struct mdev_parent_ops vfio_ccw_mdev_ops = {
+	.owner			= THIS_MODULE,
+	.supported_type_groups  = mdev_type_groups,
+	.create			= vfio_ccw_mdev_create,
+	.remove			= vfio_ccw_mdev_remove,
+};
+
 int vfio_ccw_mdev_reg(struct subchannel *sch)
 {
 	return mdev_register_device(&sch->dev, &vfio_ccw_mdev_ops);
diff --git a/drivers/s390/crypto/vfio_ap_ops.c
b/drivers/s390/crypto/vfio_ap_ops.c
index 07c31070afeb..7bdc62393112 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -16,6 +16,7 @@
 #include <linux/bitops.h>
 #include <linux/kvm_host.h>
 #include <linux/module.h>
+#include <linux/mdev_vfio_ops.h>
 #include <asm/kvm.h>
 #include <asm/zcrypt.h>
 
@@ -321,6 +322,8 @@ static void vfio_ap_matrix_init(struct ap_config_info *info,
 	matrix->adm_max = info->apxa ? info->Nd : 15;
 }
 
+static const struct mdev_vfio_device_ops mdev_vfio_ops;
+
 static int vfio_ap_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
 {
 	struct ap_matrix_mdev *matrix_mdev;
@@ -343,7 +346,7 @@ static int vfio_ap_mdev_create(struct kobject *kobj, struct
mdev_device *mdev)
 	list_add(&matrix_mdev->node, &matrix_dev->mdev_list);
 	mutex_unlock(&matrix_dev->lock);
 
-	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
+	mdev_set_vfio_ops(mdev, &mdev_vfio_ops);
 	return 0;
 }
 
@@ -1281,15 +1284,18 @@ static ssize_t vfio_ap_mdev_ioctl(struct mdev_device
*mdev,
 	return ret;
 }
 
+static const struct mdev_vfio_device_ops mdev_vfio_ops = {
+	.open			= vfio_ap_mdev_open,
+	.release		= vfio_ap_mdev_release,
+	.ioctl			= vfio_ap_mdev_ioctl,
+};
+
 static const struct mdev_parent_ops vfio_ap_matrix_ops = {
 	.owner			= THIS_MODULE,
 	.supported_type_groups	= vfio_ap_mdev_type_groups,
 	.mdev_attr_groups	= vfio_ap_mdev_attr_groups,
 	.create			= vfio_ap_mdev_create,
 	.remove			= vfio_ap_mdev_remove,
-	.open			= vfio_ap_mdev_open,
-	.release		= vfio_ap_mdev_release,
-	.ioctl			= vfio_ap_mdev_ioctl,
 };
 
 int vfio_ap_mdev_register(void)
diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
index 7bfa2e46e829..4e70f19ac145 100644
--- a/drivers/vfio/mdev/mdev_core.c
+++ b/drivers/vfio/mdev/mdev_core.c
@@ -47,7 +47,8 @@ EXPORT_SYMBOL(mdev_set_drvdata);
 
 /*
  * Specify the class for the mdev device, this must be called during
- * create() callback.
+ * create() callback explicitly or implicitly through the helpers
+ * provided by each class.
  */
 void mdev_set_class(struct mdev_device *mdev, u16 id)
 {
@@ -56,6 +57,27 @@ void mdev_set_class(struct mdev_device *mdev, u16 id)
 }
 EXPORT_SYMBOL(mdev_set_class);
 
+/*
+ * Specify the mdev device to be a VFIO mdev device, and set VFIO
+ * device ops for it. This must be called from the create() callback
+ * for VFIO mdev device.
+ */
+void mdev_set_vfio_ops(struct mdev_device *mdev,
+		       const struct mdev_vfio_device_ops *vfio_ops)
+{
+	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
+	mdev->vfio_ops = vfio_ops;
+}
+EXPORT_SYMBOL(mdev_set_vfio_ops);
+
+/* Get the VFIO device ops for the mdev device. */
+const struct mdev_vfio_device_ops *mdev_get_vfio_ops(struct mdev_device *mdev)
+{
+	WARN_ON(mdev->class_id != MDEV_CLASS_ID_VFIO);
+	return mdev->vfio_ops;
+}
+EXPORT_SYMBOL(mdev_get_vfio_ops);
+
 struct device *mdev_dev(struct mdev_device *mdev)
 {
 	return &mdev->dev;
diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
index c65f436c1869..411227373625 100644
--- a/drivers/vfio/mdev/mdev_private.h
+++ b/drivers/vfio/mdev/mdev_private.h
@@ -10,6 +10,8 @@
 #ifndef MDEV_PRIVATE_H
 #define MDEV_PRIVATE_H
 
+#include <linux/mdev_vfio_ops.h>
+
 int  mdev_bus_register(void);
 void mdev_bus_unregister(void);
 
@@ -34,6 +36,9 @@ struct mdev_device {
 	struct device *iommu_device;
 	bool active;
 	u16 class_id;
+	union {
+		const struct mdev_vfio_device_ops *vfio_ops;
+	};
 };
 
 #define to_mdev_device(dev)	container_of(dev, struct mdev_device, dev)
diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c
index a6641cd8b5a3..c01e2194e4b3 100644
--- a/drivers/vfio/mdev/vfio_mdev.c
+++ b/drivers/vfio/mdev/vfio_mdev.c
@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/vfio.h>
 #include <linux/mdev.h>
+#include <linux/mdev_vfio_ops.h>
 
 #include "mdev_private.h"
 
@@ -24,16 +25,16 @@
 static int vfio_mdev_open(void *device_data)
 {
 	struct mdev_device *mdev = device_data;
-	struct mdev_parent *parent = mdev->parent;
+	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
 	int ret;
 
-	if (unlikely(!parent->ops->open))
+	if (unlikely(!ops->open))
 		return -EINVAL;
 
 	if (!try_module_get(THIS_MODULE))
 		return -ENODEV;
 
-	ret = parent->ops->open(mdev);
+	ret = ops->open(mdev);
 	if (ret)
 		module_put(THIS_MODULE);
 
@@ -43,10 +44,10 @@ static int vfio_mdev_open(void *device_data)
 static void vfio_mdev_release(void *device_data)
 {
 	struct mdev_device *mdev = device_data;
-	struct mdev_parent *parent = mdev->parent;
+	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
 
-	if (likely(parent->ops->release))
-		parent->ops->release(mdev);
+	if (likely(ops->release))
+		ops->release(mdev);
 
 	module_put(THIS_MODULE);
 }
@@ -55,47 +56,47 @@ static long vfio_mdev_unlocked_ioctl(void *device_data,
 				     unsigned int cmd, unsigned long arg)
 {
 	struct mdev_device *mdev = device_data;
-	struct mdev_parent *parent = mdev->parent;
+	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
 
-	if (unlikely(!parent->ops->ioctl))
+	if (unlikely(!ops->ioctl))
 		return -EINVAL;
 
-	return parent->ops->ioctl(mdev, cmd, arg);
+	return ops->ioctl(mdev, cmd, arg);
 }
 
 static ssize_t vfio_mdev_read(void *device_data, char __user *buf,
 			      size_t count, loff_t *ppos)
 {
 	struct mdev_device *mdev = device_data;
-	struct mdev_parent *parent = mdev->parent;
+	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
 
-	if (unlikely(!parent->ops->read))
+	if (unlikely(!ops->read))
 		return -EINVAL;
 
-	return parent->ops->read(mdev, buf, count, ppos);
+	return ops->read(mdev, buf, count, ppos);
 }
 
 static ssize_t vfio_mdev_write(void *device_data, const char __user *buf,
 			       size_t count, loff_t *ppos)
 {
 	struct mdev_device *mdev = device_data;
-	struct mdev_parent *parent = mdev->parent;
+	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
 
-	if (unlikely(!parent->ops->write))
+	if (unlikely(!ops->write))
 		return -EINVAL;
 
-	return parent->ops->write(mdev, buf, count, ppos);
+	return ops->write(mdev, buf, count, ppos);
 }
 
 static int vfio_mdev_mmap(void *device_data, struct vm_area_struct *vma)
 {
 	struct mdev_device *mdev = device_data;
-	struct mdev_parent *parent = mdev->parent;
+	const struct mdev_vfio_device_ops *ops = mdev_get_vfio_ops(mdev);
 
-	if (unlikely(!parent->ops->mmap))
+	if (unlikely(!ops->mmap))
 		return -EINVAL;
 
-	return parent->ops->mmap(mdev, vma);
+	return ops->mmap(mdev, vma);
 }
 
 static const struct vfio_device_ops vfio_mdev_dev_ops = {
diff --git a/include/linux/mdev.h b/include/linux/mdev.h
index 78b69d09eb54..9e37506d1987 100644
--- a/include/linux/mdev.h
+++ b/include/linux/mdev.h
@@ -10,7 +10,13 @@
 #ifndef MDEV_H
 #define MDEV_H
 
+#include <linux/types.h>
+#include <linux/device.h>
+#include <linux/mdev.h>
+#include <uapi/linux/uuid.h>
+
 struct mdev_device;
+struct mdev_vfio_device_ops;
 
 /*
  * Called by the parent device driver to set the device which represents
@@ -48,30 +54,7 @@ struct device *mdev_get_iommu_device(struct device *dev);
  *			@mdev: mdev_device device structure which is being
  *			       destroyed
  *			Returns integer: success (0) or error (< 0)
- * @open:		Open mediated device.
- *			@mdev: mediated device.
- *			Returns integer: success (0) or error (< 0)
- * @release:		release mediated device
- *			@mdev: mediated device.
- * @read:		Read emulation callback
- *			@mdev: mediated device structure
- *			@buf: read buffer
- *			@count: number of bytes to read
- *			@ppos: address.
- *			Retuns number on bytes read on success or error.
- * @write:		Write emulation callback
- *			@mdev: mediated device structure
- *			@buf: write buffer
- *			@count: number of bytes to be written
- *			@ppos: address.
- *			Retuns number on bytes written on success or error.
- * @ioctl:		IOCTL callback
- *			@mdev: mediated device structure
- *			@cmd: ioctl command
- *			@arg: arguments to ioctl
- * @mmap:		mmap callback
- *			@mdev: mediated device structure
- *			@vma: vma structure
+ *
  * Parent device that support mediated device should be registered with mdev
  * module with mdev_parent_ops structure.
  **/
@@ -83,15 +66,6 @@ struct mdev_parent_ops {
 
 	int     (*create)(struct kobject *kobj, struct mdev_device *mdev);
 	int     (*remove)(struct mdev_device *mdev);
-	int     (*open)(struct mdev_device *mdev);
-	void    (*release)(struct mdev_device *mdev);
-	ssize_t (*read)(struct mdev_device *mdev, char __user *buf,
-			size_t count, loff_t *ppos);
-	ssize_t (*write)(struct mdev_device *mdev, const char __user *buf,
-			 size_t count, loff_t *ppos);
-	long	(*ioctl)(struct mdev_device *mdev, unsigned int cmd,
-			 unsigned long arg);
-	int	(*mmap)(struct mdev_device *mdev, struct vm_area_struct *vma);
 };
 
 /* interface for exporting mdev supported type attributes */
@@ -135,6 +109,9 @@ void *mdev_get_drvdata(struct mdev_device *mdev);
 void mdev_set_drvdata(struct mdev_device *mdev, void *data);
 const guid_t *mdev_uuid(struct mdev_device *mdev);
 void mdev_set_class(struct mdev_device *mdev, u16 id);
+void mdev_set_vfio_ops(struct mdev_device *mdev,
+		       const struct mdev_vfio_device_ops *vfio_ops);
+const struct mdev_vfio_device_ops *mdev_get_vfio_ops(struct mdev_device *mdev);
 
 extern struct bus_type mdev_bus_type;
 
diff --git a/include/linux/mdev_vfio_ops.h b/include/linux/mdev_vfio_ops.h
new file mode 100644
index 000000000000..317518f30621
--- /dev/null
+++ b/include/linux/mdev_vfio_ops.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * VFIO Mediated device definition
+ */
+
+#ifndef MDEV_VFIO_OPS_H
+#define MDEV_VFIO_OPS_H
+
+#include <linux/mdev.h>
+
+/**
+ * struct mdev_vfio_device_ops - Structure to be registered for each
+ * mdev device to register the device to vfio-mdev module.
+ *
+ * @open:		Open mediated device.
+ *			@mdev: mediated device.
+ *			Returns integer: success (0) or error (< 0)
+ * @release:		release mediated device
+ *			@mdev: mediated device.
+ * @read:		Read emulation callback
+ *			@mdev: mediated device structure
+ *			@buf: read buffer
+ *			@count: number of bytes to read
+ *			@ppos: address.
+ *			Retuns number on bytes read on success or error.
+ * @write:		Write emulation callback
+ *			@mdev: mediated device structure
+ *			@buf: write buffer
+ *			@count: number of bytes to be written
+ *			@ppos: address.
+ *			Retuns number on bytes written on success or error.
+ * @ioctl:		IOCTL callback
+ *			@mdev: mediated device structure
+ *			@cmd: ioctl command
+ *			@arg: arguments to ioctl
+ * @mmap:		mmap callback
+ *			@mdev: mediated device structure
+ *			@vma: vma structure
+ */
+struct mdev_vfio_device_ops {
+	int     (*open)(struct mdev_device *mdev);
+	void    (*release)(struct mdev_device *mdev);
+	ssize_t (*read)(struct mdev_device *mdev, char __user *buf,
+			size_t count, loff_t *ppos);
+	ssize_t (*write)(struct mdev_device *mdev, const char __user *buf,
+			 size_t count, loff_t *ppos);
+	long	(*ioctl)(struct mdev_device *mdev, unsigned int cmd,
+			 unsigned long arg);
+	int	(*mmap)(struct mdev_device *mdev, struct vm_area_struct *vma);
+};
+
+#endif
diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c
index 115bc5074656..12963767ba37 100644
--- a/samples/vfio-mdev/mbochs.c
+++ b/samples/vfio-mdev/mbochs.c
@@ -30,6 +30,7 @@
 #include <linux/iommu.h>
 #include <linux/sysfs.h>
 #include <linux/mdev.h>
+#include <linux/mdev_vfio_ops.h>
 #include <linux/pci.h>
 #include <linux/dma-buf.h>
 #include <linux/highmem.h>
@@ -516,6 +517,8 @@ static int mbochs_reset(struct mdev_device *mdev)
 	return 0;
 }
 
+static const struct mdev_vfio_device_ops mdev_vfio_ops;
+
 static int mbochs_create(struct kobject *kobj, struct mdev_device *mdev)
 {
 	const struct mbochs_type *type = mbochs_find_type(kobj);
@@ -561,7 +564,7 @@ static int mbochs_create(struct kobject *kobj, struct
mdev_device *mdev)
 	mbochs_reset(mdev);
 
 	mbochs_used_mbytes += type->mbytes;
-	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
+	mdev_set_vfio_ops(mdev, &mdev_vfio_ops);
 	return 0;
 
 err_mem:
@@ -1419,12 +1422,7 @@ static struct attribute_group *mdev_type_groups[] = {
 	NULL,
 };
 
-static const struct mdev_parent_ops mdev_fops = {
-	.owner			= THIS_MODULE,
-	.mdev_attr_groups	= mdev_dev_groups,
-	.supported_type_groups	= mdev_type_groups,
-	.create			= mbochs_create,
-	.remove			= mbochs_remove,
+static const struct mdev_vfio_device_ops mdev_vfio_ops = {
 	.open			= mbochs_open,
 	.release		= mbochs_close,
 	.read			= mbochs_read,
@@ -1433,6 +1431,14 @@ static const struct mdev_parent_ops mdev_fops = {
 	.mmap			= mbochs_mmap,
 };
 
+static const struct mdev_parent_ops mdev_fops = {
+	.owner			= THIS_MODULE,
+	.mdev_attr_groups	= mdev_dev_groups,
+	.supported_type_groups	= mdev_type_groups,
+	.create			= mbochs_create,
+	.remove			= mbochs_remove,
+};
+
 static const struct file_operations vd_fops = {
 	.owner		= THIS_MODULE,
 };
diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c
index 665614574d50..50ee6c98b2af 100644
--- a/samples/vfio-mdev/mdpy.c
+++ b/samples/vfio-mdev/mdpy.c
@@ -26,6 +26,7 @@
 #include <linux/iommu.h>
 #include <linux/sysfs.h>
 #include <linux/mdev.h>
+#include <linux/mdev_vfio_ops.h>
 #include <linux/pci.h>
 #include <drm/drm_fourcc.h>
 #include "mdpy-defs.h"
@@ -226,6 +227,8 @@ static int mdpy_reset(struct mdev_device *mdev)
 	return 0;
 }
 
+static const struct mdev_vfio_device_ops mdev_vfio_ops;
+
 static int mdpy_create(struct kobject *kobj, struct mdev_device *mdev)
 {
 	const struct mdpy_type *type = mdpy_find_type(kobj);
@@ -269,7 +272,7 @@ static int mdpy_create(struct kobject *kobj, struct
mdev_device *mdev)
 	mdpy_reset(mdev);
 
 	mdpy_count++;
-	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
+	mdev_set_vfio_ops(mdev, &mdev_vfio_ops);
 	return 0;
 }
 
@@ -726,12 +729,7 @@ static struct attribute_group *mdev_type_groups[] = {
 	NULL,
 };
 
-static const struct mdev_parent_ops mdev_fops = {
-	.owner			= THIS_MODULE,
-	.mdev_attr_groups	= mdev_dev_groups,
-	.supported_type_groups	= mdev_type_groups,
-	.create			= mdpy_create,
-	.remove			= mdpy_remove,
+static const struct mdev_vfio_device_ops mdev_vfio_ops = {
 	.open			= mdpy_open,
 	.release		= mdpy_close,
 	.read			= mdpy_read,
@@ -740,6 +738,14 @@ static const struct mdev_parent_ops mdev_fops = {
 	.mmap			= mdpy_mmap,
 };
 
+static const struct mdev_parent_ops mdev_fops = {
+	.owner			= THIS_MODULE,
+	.mdev_attr_groups	= mdev_dev_groups,
+	.supported_type_groups	= mdev_type_groups,
+	.create			= mdpy_create,
+	.remove			= mdpy_remove,
+};
+
 static const struct file_operations vd_fops = {
 	.owner		= THIS_MODULE,
 };
diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
index 90da12ff7fd9..be476e7ad1f8 100644
--- a/samples/vfio-mdev/mtty.c
+++ b/samples/vfio-mdev/mtty.c
@@ -27,6 +27,7 @@
 #include <linux/ctype.h>
 #include <linux/file.h>
 #include <linux/mdev.h>
+#include <linux/mdev_vfio_ops.h>
 #include <linux/pci.h>
 #include <linux/serial.h>
 #include <uapi/linux/serial_reg.h>
@@ -708,6 +709,8 @@ static ssize_t mdev_access(struct mdev_device *mdev, u8
*buf, size_t count,
 	return ret;
 }
 
+static const struct mdev_vfio_device_ops vfio_dev_ops;
+
 static int mtty_create(struct kobject *kobj, struct mdev_device *mdev)
 {
 	struct mdev_state *mdev_state;
@@ -755,7 +758,7 @@ static int mtty_create(struct kobject *kobj, struct
mdev_device *mdev)
 	list_add(&mdev_state->next, &mdev_devices_list);
 	mutex_unlock(&mdev_list_lock);
 
-	mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
+	mdev_set_vfio_ops(mdev, &vfio_dev_ops);
 	return 0;
 }
 
@@ -1388,6 +1391,14 @@ static struct attribute_group *mdev_type_groups[] = {
 	NULL,
 };
 
+static const struct mdev_vfio_device_ops vfio_dev_ops = {
+	.open		= mtty_open,
+	.release	= mtty_close,
+	.read		= mtty_read,
+	.write		= mtty_write,
+	.ioctl		= mtty_ioctl,
+};
+
 static const struct mdev_parent_ops mdev_fops = {
 	.owner                  = THIS_MODULE,
 	.dev_attr_groups        = mtty_dev_groups,
@@ -1395,11 +1406,6 @@ static const struct mdev_parent_ops mdev_fops = {
 	.supported_type_groups  = mdev_type_groups,
 	.create                 = mtty_create,
 	.remove			= mtty_remove,
-	.open                   = mtty_open,
-	.release                = mtty_close,
-	.read                   = mtty_read,
-	.write                  = mtty_write,
-	.ioctl		        = mtty_ioctl,
 };
 
 static void mtty_device_release(struct device *dev)
-- 
2.19.1

This patch implements basic support for mdev driver that supports
virtio transport for kernel virtio driver.

Reviewed-by: Cornelia Huck <cohuck at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 MAINTAINERS                      |   1 +
 drivers/vfio/mdev/mdev_core.c    |  21 +++++
 drivers/vfio/mdev/mdev_private.h |   2 +
 include/linux/mdev.h             |   6 ++
 include/linux/mdev_virtio_ops.h  | 147 +++++++++++++++++++++++++++++++
 5 files changed, 177 insertions(+)
 create mode 100644 include/linux/mdev_virtio_ops.h

diff --git a/MAINTAINERS b/MAINTAINERS
index f661d13344d6..4997957443df 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17248,6 +17248,7 @@ F:	include/linux/virtio*.h
 F:	include/uapi/linux/virtio_*.h
 F:	drivers/crypto/virtio/
 F:	mm/balloon_compaction.c
+F:	include/linux/mdev_virtio_ops.h
 
 VIRTIO BLOCK AND SCSI DRIVERS
 M:	"Michael S. Tsirkin" <mst at redhat.com>
diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
index 4e70f19ac145..c58253404ed5 100644
--- a/drivers/vfio/mdev/mdev_core.c
+++ b/drivers/vfio/mdev/mdev_core.c
@@ -78,6 +78,27 @@ const struct mdev_vfio_device_ops *mdev_get_vfio_ops(struct
mdev_device *mdev)
 }
 EXPORT_SYMBOL(mdev_get_vfio_ops);
 
+/*
+ * Specify the virtio device ops for the mdev device, this
+ * must be called during create() callback for virtio mdev device.
+ */
+void mdev_set_virtio_ops(struct mdev_device *mdev,
+			 const struct mdev_virtio_device_ops *virtio_ops)
+{
+	mdev_set_class(mdev, MDEV_CLASS_ID_VIRTIO);
+	mdev->virtio_ops = virtio_ops;
+}
+EXPORT_SYMBOL(mdev_set_virtio_ops);
+
+/* Get the virtio device ops for the mdev device. */
+const struct mdev_virtio_device_ops *
+mdev_get_virtio_ops(struct mdev_device *mdev)
+{
+	WARN_ON(mdev->class_id != MDEV_CLASS_ID_VIRTIO);
+	return mdev->virtio_ops;
+}
+EXPORT_SYMBOL(mdev_get_virtio_ops);
+
 struct device *mdev_dev(struct mdev_device *mdev)
 {
 	return &mdev->dev;
diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
index 411227373625..2c74dd032409 100644
--- a/drivers/vfio/mdev/mdev_private.h
+++ b/drivers/vfio/mdev/mdev_private.h
@@ -11,6 +11,7 @@
 #define MDEV_PRIVATE_H
 
 #include <linux/mdev_vfio_ops.h>
+#include <linux/mdev_virtio_ops.h>
 
 int  mdev_bus_register(void);
 void mdev_bus_unregister(void);
@@ -38,6 +39,7 @@ struct mdev_device {
 	u16 class_id;
 	union {
 		const struct mdev_vfio_device_ops *vfio_ops;
+		const struct mdev_virtio_device_ops *virtio_ops;
 	};
 };
 
diff --git a/include/linux/mdev.h b/include/linux/mdev.h
index 9e37506d1987..f3d75a60c2b5 100644
--- a/include/linux/mdev.h
+++ b/include/linux/mdev.h
@@ -17,6 +17,7 @@
 
 struct mdev_device;
 struct mdev_vfio_device_ops;
+struct mdev_virtio_device_ops;
 
 /*
  * Called by the parent device driver to set the device which represents
@@ -112,6 +113,10 @@ void mdev_set_class(struct mdev_device *mdev, u16 id);
 void mdev_set_vfio_ops(struct mdev_device *mdev,
 		       const struct mdev_vfio_device_ops *vfio_ops);
 const struct mdev_vfio_device_ops *mdev_get_vfio_ops(struct mdev_device *mdev);
+void mdev_set_virtio_ops(struct mdev_device *mdev,
+			 const struct mdev_virtio_device_ops *virtio_ops);
+const struct mdev_virtio_device_ops *
+mdev_get_virtio_ops(struct mdev_device *mdev);
 
 extern struct bus_type mdev_bus_type;
 
@@ -127,6 +132,7 @@ struct mdev_device *mdev_from_dev(struct device *dev);
 
 enum {
 	MDEV_CLASS_ID_VFIO = 1,
+	MDEV_CLASS_ID_VIRTIO = 2,
 	/* New entries must be added here */
 };
 
diff --git a/include/linux/mdev_virtio_ops.h b/include/linux/mdev_virtio_ops.h
new file mode 100644
index 000000000000..8951331c6629
--- /dev/null
+++ b/include/linux/mdev_virtio_ops.h
@@ -0,0 +1,147 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Virtio mediated device driver
+ *
+ * Copyright 2019, Red Hat Corp.
+ *     Author: Jason Wang <jasowang at redhat.com>
+ */
+#ifndef MDEV_VIRTIO_OPS_H
+#define MDEV_VIRTIO_OPS_H
+
+#include <linux/interrupt.h>
+#include <linux/mdev.h>
+#include <uapi/linux/vhost.h>
+
+#define VIRTIO_MDEV_DEVICE_API_STRING		"virtio-mdev"
+
+struct virtio_mdev_callback {
+	irqreturn_t (*callback)(void *data);
+	void *private;
+};
+
+/**
+ * struct mdev_virtio_device_ops - Structure to be registered for each
+ * mdev device to register the device for virtio/vhost drivers.
+ *
+ * The callbacks are mandatory unless explicitly mentioned.
+ *
+ * @set_vq_address:		Set the address of virtqueue
+ *				@mdev: mediated device
+ *				@idx: virtqueue index
+ *				@desc_area: address of desc area
+ *				@driver_area: address of driver area
+ *				@device_area: address of device area
+ *				Returns integer: success (0) or error (< 0)
+ * @set_vq_num:			Set the size of virtqueue
+ *				@mdev: mediated device
+ *				@idx: virtqueue index
+ *				@num: the size of virtqueue
+ * @kick_vq:			Kick the virtqueue
+ *				@mdev: mediated device
+ *				@idx: virtqueue index
+ * @set_vq_cb:			Set the interrupt callback function for
+ *				a virtqueue
+ *				@mdev: mediated device
+ *				@idx: virtqueue index
+ *				@cb: virtio-mdev interrupt callback structure
+ * @set_vq_ready:		Set ready status for a virtqueue
+ *				@mdev: mediated device
+ *				@idx: virtqueue index
+ *				@ready: ready (true) not ready(false)
+ * @get_vq_ready:		Get ready status for a virtqueue
+ *				@mdev: mediated device
+ *				@idx: virtqueue index
+ *				Returns boolean: ready (true) or not (false)
+ * @set_vq_state:		Set the state for a virtqueue
+ *				@mdev: mediated device
+ *				@idx: virtqueue index
+ *				@state: virtqueue state (last_avail_idx)
+ *				Returns integer: success (0) or error (< 0)
+ * @get_vq_state:		Get the state for a virtqueue
+ *				@mdev: mediated device
+ *				@idx: virtqueue index
+ *				Returns virtqueue state (last_avail_idx)
+ * @get_vq_align:		Get the virtqueue align requirement
+ *				for the device
+ *				@mdev: mediated device
+ *				Returns virtqueue algin requirement
+ * @get_features:		Get virtio features supported by the device
+ *				@mdev: mediated device
+ *				Returns the virtio features support by the
+ *				device
+ * @set_features:		Set virtio features supported by the driver
+ *				@mdev: mediated device
+ *				@features: feature support by the driver
+ *				Returns integer: success (0) or error (< 0)
+ * @set_config_cb:		Set the config interrupt callback
+ *				@mdev: mediated device
+ *				@cb: virtio-mdev interrupt callback structure
+ * @get_vq_num_max:		Get the max size of virtqueue
+ *				@mdev: mediated device
+ *				Returns u16: max size of virtqueue
+ * @get_device_id:		Get virtio device id
+ *				@mdev: mediated device
+ *				Returns u32: virtio device id
+ * @get_vendor_id:		Get id for the vendor that provides this device
+ *				@mdev: mediated device
+ *				Returns u32: virtio vendor id
+ * @get_status:			Get the device status
+ *				@mdev: mediated device
+ *				Returns u8: virtio device status
+ * @set_status:			Set the device status
+ *				@mdev: mediated device
+ *				@status: virtio device status
+ * @get_config:			Read from device specific configuration space
+ *				@mdev: mediated device
+ *				@offset: offset from the beginning of
+ *				configuration space
+ *				@buf: buffer used to read to
+ *				@len: the length to read from
+ *				configration space
+ * @set_config:			Write to device specific configuration space
+ *				@mdev: mediated device
+ *				@offset: offset from the beginning of
+ *				configuration space
+ *				@buf: buffer used to write from
+ *				@len: the length to write to
+ *				configration space
+ * @get_generation:		Get device config generaton (optional)
+ *				@mdev: mediated device
+ *				Returns u32: device generation
+ */
+struct mdev_virtio_device_ops {
+	/* Virtqueue ops */
+	int (*set_vq_address)(struct mdev_device *mdev,
+			      u16 idx, u64 desc_area, u64 driver_area,
+			      u64 device_area);
+	void (*set_vq_num)(struct mdev_device *mdev, u16 idx, u32 num);
+	void (*kick_vq)(struct mdev_device *mdev, u16 idx);
+	void (*set_vq_cb)(struct mdev_device *mdev, u16 idx,
+			  struct virtio_mdev_callback *cb);
+	void (*set_vq_ready)(struct mdev_device *mdev, u16 idx, bool ready);
+	bool (*get_vq_ready)(struct mdev_device *mdev, u16 idx);
+	int (*set_vq_state)(struct mdev_device *mdev, u16 idx, u64 state);
+	u64 (*get_vq_state)(struct mdev_device *mdev, u16 idx);
+
+	/* Virtio device ops */
+	u16 (*get_vq_align)(struct mdev_device *mdev);
+	u64 (*get_features)(struct mdev_device *mdev);
+	int (*set_features)(struct mdev_device *mdev, u64 features);
+	void (*set_config_cb)(struct mdev_device *mdev,
+			      struct virtio_mdev_callback *cb);
+	u16 (*get_vq_num_max)(struct mdev_device *mdev);
+	u32 (*get_device_id)(struct mdev_device *mdev);
+	u32 (*get_vendor_id)(struct mdev_device *mdev);
+	u8 (*get_status)(struct mdev_device *mdev);
+	void (*set_status)(struct mdev_device *mdev, u8 status);
+	void (*get_config)(struct mdev_device *mdev, unsigned int offset,
+			   void *buf, unsigned int len);
+	void (*set_config)(struct mdev_device *mdev, unsigned int offset,
+			   const void *buf, unsigned int len);
+	u32 (*get_generation)(struct mdev_device *mdev);
+};
+
+void mdev_set_virtio_ops(struct mdev_device *mdev,
+			 const struct mdev_virtio_device_ops *virtio_ops);
+
+#endif
-- 
2.19.1

This patch introduces a new mdev transport for virtio. This is used to
use kernel virtio driver to drive the mediated device that is capable
of populating virtqueue directly.

A new virtio-mdev driver will be registered to the mdev bus, when a
new virtio-mdev device is probed, it will register the device with
mdev based config ops. This means it is a software transport between
mdev driver and mdev device. The transport was implemented through
virtio device specific ops.

Reviewed-by: Cornelia Huck <cohuck at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/virtio/Kconfig       |  13 ++
 drivers/virtio/Makefile      |   1 +
 drivers/virtio/virtio_mdev.c | 406 +++++++++++++++++++++++++++++++++++
 3 files changed, 420 insertions(+)
 create mode 100644 drivers/virtio/virtio_mdev.c

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 078615cf2afc..bf526ce0facc 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -43,6 +43,19 @@ config VIRTIO_PCI_LEGACY
 
 	  If unsure, say Y.
 
+config VIRTIO_MDEV
+	tristate "MDEV driver for virtio devices"
+	depends on VFIO_MDEV && VIRTIO
+	default n
+	help
+	  This driver provides support for virtio based paravirtual
+	  device driver over MDEV bus. For this to be useful, you need
+	  an appropriate virtio mdev device implementation that
+	  operates on a physical device to allow the datapath of virtio
+	  to be offloaded to hardware.
+
+	  If unsure, say M.
+
 config VIRTIO_PMEM
 	tristate "Support for virtio pmem driver"
 	depends on VIRTIO
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 3a2b5c5dcf46..f2997b6c812f 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -6,3 +6,4 @@ virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
 virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
 obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
 obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
+obj-$(CONFIG_VIRTIO_MDEV) += virtio_mdev.o
diff --git a/drivers/virtio/virtio_mdev.c b/drivers/virtio/virtio_mdev.c
new file mode 100644
index 000000000000..9e12ef240493
--- /dev/null
+++ b/drivers/virtio/virtio_mdev.c
@@ -0,0 +1,406 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * VIRTIO based driver for Mediated device
+ *
+ * Copyright (c) 2019, Red Hat. All rights reserved.
+ *     Author: Jason Wang <jasowang at redhat.com>
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/uuid.h>
+#include <linux/mdev.h>
+#include <linux/mdev_virtio_ops.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_ring.h>
+
+#define DRIVER_VERSION  "0.1"
+#define DRIVER_AUTHOR   "Red Hat Corporation"
+#define DRIVER_DESC     "VIRTIO based driver for Mediated device"
+
+#define to_virtio_mdev_device(dev) \
+	container_of(dev, struct virtio_mdev_device, vdev)
+
+struct virtio_mdev_device {
+	struct virtio_device vdev;
+	struct mdev_device *mdev;
+	u64 features;
+
+	/* The lock to protect virtqueue list */
+	spinlock_t lock;
+	/* List of virtio_mdev_vq_info */
+	struct list_head virtqueues;
+};
+
+struct virtio_mdev_vq_info {
+	/* the actual virtqueue */
+	struct virtqueue *vq;
+
+	/* the list node for the virtqueues list */
+	struct list_head node;
+};
+
+static struct mdev_device *vm_get_mdev(struct virtio_device *vdev)
+{
+	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
+	struct mdev_device *mdev = vm_dev->mdev;
+
+	return mdev;
+}
+
+static void virtio_mdev_get(struct virtio_device *vdev, unsigned offset,
+			    void *buf, unsigned len)
+{
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	ops->get_config(mdev, offset, buf, len);
+}
+
+static void virtio_mdev_set(struct virtio_device *vdev, unsigned offset,
+			    const void *buf, unsigned len)
+{
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	ops->set_config(mdev, offset, buf, len);
+}
+
+static u32 virtio_mdev_generation(struct virtio_device *vdev)
+{
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	if (ops->get_generation)
+		return ops->get_generation(mdev);
+
+	return 0;
+}
+
+static u8 virtio_mdev_get_status(struct virtio_device *vdev)
+{
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	return ops->get_status(mdev);
+}
+
+static void virtio_mdev_set_status(struct virtio_device *vdev, u8 status)
+{
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	return ops->set_status(mdev, status);
+}
+
+static void virtio_mdev_reset(struct virtio_device *vdev)
+{
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	return ops->set_status(mdev, 0);
+}
+
+static bool virtio_mdev_notify(struct virtqueue *vq)
+{
+	struct mdev_device *mdev = vm_get_mdev(vq->vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	ops->kick_vq(mdev, vq->index);
+
+	return true;
+}
+
+static irqreturn_t virtio_mdev_config_cb(void *private)
+{
+	struct virtio_mdev_device *vm_dev = private;
+
+	virtio_config_changed(&vm_dev->vdev);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t virtio_mdev_virtqueue_cb(void *private)
+{
+	struct virtio_mdev_vq_info *info = private;
+
+	return vring_interrupt(0, info->vq);
+}
+
+static struct virtqueue *
+virtio_mdev_setup_vq(struct virtio_device *vdev, unsigned int index,
+		     void (*callback)(struct virtqueue *vq),
+		     const char *name, bool ctx)
+{
+	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+	struct virtio_mdev_vq_info *info;
+	struct virtio_mdev_callback cb;
+	struct virtqueue *vq;
+	u64 desc_addr, driver_addr, device_addr;
+	unsigned long flags;
+	u32 align, num;
+	int err;
+
+	if (!name)
+		return NULL;
+
+	/* Queue shouldn't already be set up. */
+	if (ops->get_vq_ready(mdev, index))
+		return ERR_PTR(-ENOENT);
+
+	/* Allocate and fill out our active queue description */
+	info = kmalloc(sizeof(*info), GFP_KERNEL);
+	if (!info)
+		return ERR_PTR(-ENOMEM);
+
+	num = ops->get_vq_num_max(mdev);
+	if (num == 0) {
+		err = -ENOENT;
+		goto error_new_virtqueue;
+	}
+
+	/* Create the vring */
+	align = ops->get_vq_align(mdev);
+	vq = vring_create_virtqueue(index, num, align, vdev,
+				    true, true, ctx,
+				    virtio_mdev_notify, callback, name);
+	if (!vq) {
+		err = -ENOMEM;
+		goto error_new_virtqueue;
+	}
+
+	/* Setup virtqueue callback */
+	cb.callback = virtio_mdev_virtqueue_cb;
+	cb.private = info;
+	ops->set_vq_cb(mdev, index, &cb);
+	ops->set_vq_num(mdev, index, virtqueue_get_vring_size(vq));
+
+	desc_addr = virtqueue_get_desc_addr(vq);
+	driver_addr = virtqueue_get_avail_addr(vq);
+	device_addr = virtqueue_get_used_addr(vq);
+
+	if (ops->set_vq_address(mdev, index,
+				desc_addr, driver_addr,
+				device_addr)) {
+		err = -EINVAL;
+		goto err_vq;
+	}
+
+	ops->set_vq_ready(mdev, index, 1);
+
+	vq->priv = info;
+	info->vq = vq;
+
+	spin_lock_irqsave(&vm_dev->lock, flags);
+	list_add(&info->node, &vm_dev->virtqueues);
+	spin_unlock_irqrestore(&vm_dev->lock, flags);
+
+	return vq;
+
+err_vq:
+	vring_del_virtqueue(vq);
+error_new_virtqueue:
+	ops->set_vq_ready(mdev, index, 0);
+	WARN_ON(ops->get_vq_ready(mdev, index));
+	kfree(info);
+	return ERR_PTR(err);
+}
+
+static void virtio_mdev_del_vq(struct virtqueue *vq)
+{
+	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vq->vdev);
+	struct mdev_device *mdev = vm_dev->mdev;
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+	struct virtio_mdev_vq_info *info = vq->priv;
+	unsigned int index = vq->index;
+	unsigned long flags;
+
+	spin_lock_irqsave(&vm_dev->lock, flags);
+	list_del(&info->node);
+	spin_unlock_irqrestore(&vm_dev->lock, flags);
+
+	/* Select and deactivate the queue */
+	ops->set_vq_ready(mdev, index, 0);
+	WARN_ON(ops->get_vq_ready(mdev, index));
+
+	vring_del_virtqueue(vq);
+
+	kfree(info);
+}
+
+static void virtio_mdev_del_vqs(struct virtio_device *vdev)
+{
+	struct virtqueue *vq, *n;
+
+	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
+		virtio_mdev_del_vq(vq);
+}
+
+static int virtio_mdev_find_vqs(struct virtio_device *vdev, unsigned nvqs,
+				struct virtqueue *vqs[],
+				vq_callback_t *callbacks[],
+				const char * const names[],
+				const bool *ctx,
+				struct irq_affinity *desc)
+{
+	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+	struct virtio_mdev_callback cb;
+	int i, err, queue_idx = 0;
+
+	for (i = 0; i < nvqs; ++i) {
+		if (!names[i]) {
+			vqs[i] = NULL;
+			continue;
+		}
+
+		vqs[i] = virtio_mdev_setup_vq(vdev, queue_idx++,
+					      callbacks[i], names[i], ctx ?
+					      ctx[i] : false);
+		if (IS_ERR(vqs[i])) {
+			err = PTR_ERR(vqs[i]);
+			goto err_setup_vq;
+		}
+	}
+
+	cb.callback = virtio_mdev_config_cb;
+	cb.private = vm_dev;
+	ops->set_config_cb(mdev, &cb);
+
+	return 0;
+
+err_setup_vq:
+	virtio_mdev_del_vqs(vdev);
+	return err;
+}
+
+static u64 virtio_mdev_get_features(struct virtio_device *vdev)
+{
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	return ops->get_features(mdev);
+}
+
+static int virtio_mdev_finalize_features(struct virtio_device *vdev)
+{
+	struct mdev_device *mdev = vm_get_mdev(vdev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+
+	/* Give virtio_ring a chance to accept features. */
+	vring_transport_features(vdev);
+
+	return ops->set_features(mdev, vdev->features);
+}
+
+static const char *virtio_mdev_bus_name(struct virtio_device *vdev)
+{
+	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
+	struct mdev_device *mdev = vm_dev->mdev;
+
+	return dev_name(mdev_dev(mdev));
+}
+
+static const struct virtio_config_ops virtio_mdev_config_ops = {
+	.get		= virtio_mdev_get,
+	.set		= virtio_mdev_set,
+	.generation	= virtio_mdev_generation,
+	.get_status	= virtio_mdev_get_status,
+	.set_status	= virtio_mdev_set_status,
+	.reset		= virtio_mdev_reset,
+	.find_vqs	= virtio_mdev_find_vqs,
+	.del_vqs	= virtio_mdev_del_vqs,
+	.get_features	= virtio_mdev_get_features,
+	.finalize_features = virtio_mdev_finalize_features,
+	.bus_name	= virtio_mdev_bus_name,
+};
+
+static void virtio_mdev_release_dev(struct device *_d)
+{
+	struct virtio_device *vdev +	       container_of(_d, struct virtio_device,
dev);
+	struct virtio_mdev_device *vm_dev +	       container_of(vdev, struct
virtio_mdev_device, vdev);
+	struct mdev_device *mdev = vm_dev->mdev;
+
+	devm_kfree(mdev_dev(mdev), vm_dev);
+}
+
+static int virtio_mdev_probe(struct device *dev)
+{
+	struct mdev_device *mdev = mdev_from_dev(dev);
+	const struct mdev_virtio_device_ops *ops = mdev_get_virtio_ops(mdev);
+	struct virtio_mdev_device *vm_dev;
+	int rc;
+
+	vm_dev = devm_kzalloc(dev, sizeof(*vm_dev), GFP_KERNEL);
+	if (!vm_dev)
+		return -ENOMEM;
+
+	vm_dev->vdev.dev.parent = dev;
+	vm_dev->vdev.dev.release = virtio_mdev_release_dev;
+	vm_dev->vdev.config = &virtio_mdev_config_ops;
+	vm_dev->mdev = mdev;
+	INIT_LIST_HEAD(&vm_dev->virtqueues);
+	spin_lock_init(&vm_dev->lock);
+
+	vm_dev->vdev.id.device = ops->get_device_id(mdev);
+	if (vm_dev->vdev.id.device == 0)
+		return -ENODEV;
+
+	vm_dev->vdev.id.vendor = ops->get_vendor_id(mdev);
+	rc = register_virtio_device(&vm_dev->vdev);
+	if (rc)
+		put_device(dev);
+	else
+		dev_set_drvdata(dev, vm_dev);
+
+	return rc;
+}
+
+static void virtio_mdev_remove(struct device *dev)
+{
+	struct virtio_mdev_device *vm_dev = dev_get_drvdata(dev);
+
+	unregister_virtio_device(&vm_dev->vdev);
+}
+
+static const struct mdev_class_id virtio_id_table[] = {
+	{ MDEV_CLASS_ID_VIRTIO },
+	{ 0 },
+};
+
+MODULE_DEVICE_TABLE(mdev, virtio_id_table);
+
+static struct mdev_driver virtio_mdev_driver = {
+	.name	= "virtio_mdev",
+	.probe	= virtio_mdev_probe,
+	.remove = virtio_mdev_remove,
+	.id_table = virtio_id_table,
+};
+
+static int __init virtio_mdev_init(void)
+{
+	return mdev_register_driver(&virtio_mdev_driver, THIS_MODULE);
+}
+
+static void __exit virtio_mdev_exit(void)
+{
+	mdev_unregister_driver(&virtio_mdev_driver);
+}
+
+module_init(virtio_mdev_init)
+module_exit(virtio_mdev_exit)
+
+MODULE_VERSION(DRIVER_VERSION);
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);
-- 
2.19.1

This sample driver creates mdev device that simulate virtio net device
over virtio mdev transport. The device is implemented through vringh
and workqueue. A device specific dma ops is to make sure HVA is used
directly as the IOVA. This should be sufficient for kernel virtio
driver to work.

Only 'virtio' type is supported right now. I plan to add 'vhost'
type
on top which requires some virtual IOMMU implemented in this sample
driver.

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 MAINTAINERS                        |   1 +
 samples/Kconfig                    |  10 +
 samples/vfio-mdev/Makefile         |   1 +
 samples/vfio-mdev/mvnet_loopback.c | 687 +++++++++++++++++++++++++++++
 4 files changed, 699 insertions(+)
 create mode 100644 samples/vfio-mdev/mvnet_loopback.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 4997957443df..62c3eafa99b0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17249,6 +17249,7 @@ F:	include/uapi/linux/virtio_*.h
 F:	drivers/crypto/virtio/
 F:	mm/balloon_compaction.c
 F:	include/linux/mdev_virtio_ops.h
+F:	samples/vfio-mdev/mvnet_loopback.c
 
 VIRTIO BLOCK AND SCSI DRIVERS
 M:	"Michael S. Tsirkin" <mst at redhat.com>
diff --git a/samples/Kconfig b/samples/Kconfig
index c8dacb4dda80..5b347e90fd20 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -131,6 +131,16 @@ config SAMPLE_VFIO_MDEV_MDPY
 	  mediated device.  It is a simple framebuffer and supports
 	  the region display interface (VFIO_GFX_PLANE_TYPE_REGION).
 
+config SAMPLE_VIRTIO_MDEV_NET_LOOPBACK
+	tristate "Build loopback VIRTIO net example mediated device sample code
-- loadable modules only"
+	depends on VIRTIO_MDEV && VHOST_RING && m
+	help
+	  Build a networking sample device for use as a virtio
+	  mediated device. The device cooperates with virtio-mdev bus
+	  driver to present an virtio ethernet driver for
+	  kernel. It simply loopbacks all packets from its TX
+	  virtqueue to its RX virtqueue.
+
 config SAMPLE_VFIO_MDEV_MDPY_FB
 	tristate "Build VFIO mdpy example guest fbdev driver -- loadable module
only"
 	depends on FB && m
diff --git a/samples/vfio-mdev/Makefile b/samples/vfio-mdev/Makefile
index 10d179c4fdeb..817618569848 100644
--- a/samples/vfio-mdev/Makefile
+++ b/samples/vfio-mdev/Makefile
@@ -3,3 +3,4 @@ obj-$(CONFIG_SAMPLE_VFIO_MDEV_MTTY) += mtty.o
 obj-$(CONFIG_SAMPLE_VFIO_MDEV_MDPY) += mdpy.o
 obj-$(CONFIG_SAMPLE_VFIO_MDEV_MDPY_FB) += mdpy-fb.o
 obj-$(CONFIG_SAMPLE_VFIO_MDEV_MBOCHS) += mbochs.o
+obj-$(CONFIG_SAMPLE_VIRTIO_MDEV_NET_LOOPBACK) += mvnet_loopback.o
diff --git a/samples/vfio-mdev/mvnet_loopback.c
b/samples/vfio-mdev/mvnet_loopback.c
new file mode 100644
index 000000000000..e790004ddeb9
--- /dev/null
+++ b/samples/vfio-mdev/mvnet_loopback.c
@@ -0,0 +1,687 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Mediated virtual virtio-net device driver.
+ *
+ * Copyright (c) 2019, Red Hat Inc. All rights reserved.
+ *     Author: Jason Wang <jasowang at redhat.com>
+ *
+ * Sample driver that creates mdev device that simulates ethernet loopback
+ * device.
+ *
+ * Usage:
+ *
+ * # modprobe virtio_mdev
+ * # modprobe mvnet_loopback
+ * # cd /sys/devices/virtual/mvnet_loopback/mvnet_loopback/ \
+ *      mdev_supported_types/mvnet_loopback-virtio
+ * # echo "83b8f4f2-509f-382f-3c1e-e6bfe0fa1001" > ./create
+ * # cd devices/83b8f4f2-509f-382f-3c1e-e6bfe0fa1001
+ * # ls -d virtio0
+ * virtio0
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/poll.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/uuid.h>
+#include <linux/iommu.h>
+#include <linux/sysfs.h>
+#include <linux/file.h>
+#include <linux/etherdevice.h>
+#include <linux/mdev.h>
+#include <linux/vringh.h>
+#include <linux/mdev_virtio_ops.h>
+#include <uapi/linux/virtio_config.h>
+#include <uapi/linux/virtio_net.h>
+
+#define VERSION_STRING  "0.1"
+#define DRIVER_AUTHOR   "Red Hat Corporation"
+
+#define MVNET_CLASS_NAME "mvnet_loopback"
+#define MVNET_NAME       "mvnet_loopback"
+
+/*
+ * Global Structures
+ */
+
+static struct mvnet_dev {
+	struct class	*vd_class;
+	struct idr	vd_idr;
+	struct device	dev;
+} mvnet_dev;
+
+struct mvnet_virtqueue {
+	struct vringh vring;
+	struct vringh_kiov iov;
+	unsigned short head;
+	bool ready;
+	u64 desc_addr;
+	u64 device_addr;
+	u64 driver_addr;
+	u32 num;
+	void *private;
+	irqreturn_t (*cb)(void *data);
+};
+
+#define MVNET_QUEUE_ALIGN PAGE_SIZE
+#define MVNET_QUEUE_MAX 256
+#define MVNET_DEVICE_ID 0x1
+#define MVNET_VENDOR_ID 0
+
+u64 mvnet_features = (1ULL << VIRTIO_F_ANY_LAYOUT) |
+		     (1ULL << VIRTIO_F_VERSION_1) |
+		     (1ULL << VIRTIO_F_IOMMU_PLATFORM);
+
+/* State of each mdev device */
+struct mvnet_state {
+	struct mvnet_virtqueue vqs[2];
+	struct work_struct work;
+	/* spinlock to synchronize virtqueue state */
+	spinlock_t lock;
+	struct mdev_device *mdev;
+	struct virtio_net_config config;
+	void *buffer;
+	u32 status;
+	u32 generation;
+	u64 features;
+	struct list_head next;
+};
+
+static struct mutex mdev_list_lock;
+static struct list_head mdev_devices_list;
+
+static void mvnet_queue_ready(struct mvnet_state *mvnet, unsigned int idx)
+{
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+	int ret;
+
+	ret = vringh_init_kern(&vq->vring, mvnet_features, MVNET_QUEUE_MAX,
+			       false, (struct vring_desc *)vq->desc_addr,
+			       (struct vring_avail *)vq->driver_addr,
+			       (struct vring_used *)vq->device_addr);
+}
+
+static void mvnet_vq_reset(struct mvnet_virtqueue *vq)
+{
+	vq->ready = 0;
+	vq->desc_addr = 0;
+	vq->driver_addr = 0;
+	vq->device_addr = 0;
+	vq->cb = NULL;
+	vq->private = NULL;
+	vringh_init_kern(&vq->vring, mvnet_features, MVNET_QUEUE_MAX,
+			 false, 0, 0, 0);
+}
+
+static void mvnet_reset(struct mvnet_state *mvnet)
+{
+	int i;
+
+	for (i = 0; i < 2; i++)
+		mvnet_vq_reset(&mvnet->vqs[i]);
+
+	mvnet->features = 0;
+	mvnet->status = 0;
+	++mvnet->generation;
+}
+
+static void mvnet_work(struct work_struct *work)
+{
+	struct mvnet_state *mvnet = container_of(work, struct
+						 mvnet_state, work);
+	struct mvnet_virtqueue *txq = &mvnet->vqs[1];
+	struct mvnet_virtqueue *rxq = &mvnet->vqs[0];
+	size_t read, write, total_write;
+	int err;
+	int pkts = 0;
+
+	spin_lock(&mvnet->lock);
+
+	if (!txq->ready || !rxq->ready)
+		goto out;
+
+	while (true) {
+		total_write = 0;
+		err = vringh_getdesc_kern(&txq->vring, &txq->iov, NULL,
+					  &txq->head, GFP_ATOMIC);
+		if (err <= 0)
+			break;
+
+		err = vringh_getdesc_kern(&rxq->vring, NULL, &rxq->iov,
+					  &rxq->head, GFP_ATOMIC);
+		if (err <= 0) {
+			vringh_complete_kern(&txq->vring, txq->head, 0);
+			break;
+		}
+
+		while (true) {
+			read = vringh_iov_pull_kern(&txq->iov, mvnet->buffer,
+						    PAGE_SIZE);
+			if (read <= 0)
+				break;
+
+			write = vringh_iov_push_kern(&rxq->iov, mvnet->buffer,
+						     read);
+			if (write <= 0)
+				break;
+
+			total_write += write;
+		}
+
+		/* Make sure data is wrote before advancing index */
+		smp_wmb();
+
+		vringh_complete_kern(&txq->vring, txq->head, 0);
+		vringh_complete_kern(&rxq->vring, rxq->head, total_write);
+
+		/* Make sure used is visible before rasing the interrupt. */
+		smp_wmb();
+
+		local_bh_disable();
+		if (txq->cb)
+			txq->cb(txq->private);
+		if (rxq->cb)
+			rxq->cb(rxq->private);
+		local_bh_enable();
+
+		if (++pkts > 4) {
+			schedule_work(&mvnet->work);
+			goto out;
+		}
+	}
+
+out:
+	spin_unlock(&mvnet->lock);
+}
+
+static dma_addr_t mvnet_map_page(struct device *dev, struct page *page,
+				 unsigned long offset, size_t size,
+				 enum dma_data_direction dir,
+				 unsigned long attrs)
+{
+	/* Vringh can only use HVA */
+	return (dma_addr_t)(page_address(page) + offset);
+}
+
+static void mvnet_unmap_page(struct device *dev, dma_addr_t dma_addr,
+			     size_t size, enum dma_data_direction dir,
+			     unsigned long attrs)
+{
+}
+
+static void *mvnet_alloc_coherent(struct device *dev, size_t size,
+				  dma_addr_t *dma_addr, gfp_t flag,
+				  unsigned long attrs)
+{
+	void *addr = kmalloc(size, flag);
+
+	if (!addr)
+		*dma_addr = DMA_MAPPING_ERROR;
+	else
+		*dma_addr = (dma_addr_t)addr;
+
+	return addr;
+}
+
+static void mvnet_free_coherent(struct device *dev, size_t size,
+				void *vaddr, dma_addr_t dma_addr,
+				unsigned long attrs)
+{
+	kfree((void *)dma_addr);
+}
+
+static const struct dma_map_ops mvnet_dma_ops = {
+	.map_page = mvnet_map_page,
+	.unmap_page = mvnet_unmap_page,
+	.alloc = mvnet_alloc_coherent,
+	.free = mvnet_free_coherent,
+};
+
+static const struct mdev_virtio_device_ops mdev_virtio_ops;
+
+static int mvnet_create(struct kobject *kobj, struct mdev_device *mdev)
+{
+	struct mvnet_state *mvnet;
+	struct virtio_net_config *config;
+	struct device *dev = mdev_dev(mdev);
+
+	if (!mdev)
+		return -EINVAL;
+
+	mvnet = kzalloc(sizeof(*mvnet), GFP_KERNEL);
+	if (!mvnet)
+		return -ENOMEM;
+
+	mvnet->buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!mvnet->buffer) {
+		kfree(mvnet);
+		return -ENOMEM;
+	}
+
+	config = &mvnet->config;
+	config->mtu = 1500;
+	config->status = VIRTIO_NET_S_LINK_UP;
+	eth_random_addr(config->mac);
+
+	INIT_WORK(&mvnet->work, mvnet_work);
+
+	spin_lock_init(&mvnet->lock);
+	mvnet->mdev = mdev;
+	mdev_set_drvdata(mdev, mvnet);
+
+	mutex_lock(&mdev_list_lock);
+	list_add(&mvnet->next, &mdev_devices_list);
+	mutex_unlock(&mdev_list_lock);
+
+	dev->coherent_dma_mask = DMA_BIT_MASK(64);
+	set_dma_ops(dev, &mvnet_dma_ops);
+
+	mdev_set_virtio_ops(mdev, &mdev_virtio_ops);
+
+	return 0;
+}
+
+static int mvnet_remove(struct mdev_device *mdev)
+{
+	struct mvnet_state *mds, *tmp_mds;
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	int ret = -EINVAL;
+
+	mutex_lock(&mdev_list_lock);
+	list_for_each_entry_safe(mds, tmp_mds, &mdev_devices_list, next) {
+		if (mvnet == mds) {
+			list_del(&mvnet->next);
+			mdev_set_drvdata(mdev, NULL);
+			kfree(mvnet->buffer);
+			kfree(mvnet);
+			ret = 0;
+			break;
+		}
+	}
+	mutex_unlock(&mdev_list_lock);
+
+	return ret;
+}
+
+static ssize_t
+sample_mvnet_dev_show(struct device *dev, struct device_attribute *attr,
+		      char *buf)
+{
+	if (mdev_from_dev(dev))
+		return sprintf(buf, "This is MDEV %s\n", dev_name(dev));
+
+	return sprintf(buf, "\n");
+}
+
+static DEVICE_ATTR_RO(sample_mvnet_dev);
+
+static struct attribute *mvnet_dev_attrs[] = {
+	&dev_attr_sample_mvnet_dev.attr,
+	NULL,
+};
+
+static const struct attribute_group mvnet_dev_group = {
+	.name  = "mvnet_dev",
+	.attrs = mvnet_dev_attrs,
+};
+
+static const struct attribute_group *mvnet_dev_groups[] = {
+	&mvnet_dev_group,
+	NULL,
+};
+
+static ssize_t
+sample_mdev_dev_show(struct device *dev, struct device_attribute *attr,
+		     char *buf)
+{
+	if (mdev_from_dev(dev))
+		return sprintf(buf, "This is MDEV %s\n", dev_name(dev));
+
+	return sprintf(buf, "\n");
+}
+
+static DEVICE_ATTR_RO(sample_mdev_dev);
+
+static struct attribute *mdev_dev_attrs[] = {
+	&dev_attr_sample_mdev_dev.attr,
+	NULL,
+};
+
+static const struct attribute_group mdev_dev_group = {
+	.name  = "vendor",
+	.attrs = mdev_dev_attrs,
+};
+
+static const struct attribute_group *mdev_dev_groups[] = {
+	&mdev_dev_group,
+	NULL,
+};
+
+#define MVNET_STRING_LEN 16
+
+static ssize_t
+name_show(struct kobject *kobj, struct device *dev, char *buf)
+{
+	char name[MVNET_STRING_LEN];
+	const char *name_str = "virtio-net";
+
+	snprintf(name, MVNET_STRING_LEN, "%s", dev_driver_string(dev));
+	if (!strcmp(kobj->name, name))
+		return sprintf(buf, "%s\n", name_str);
+
+	return -EINVAL;
+}
+
+static MDEV_TYPE_ATTR_RO(name);
+
+static ssize_t
+available_instances_show(struct kobject *kobj, struct device *dev, char *buf)
+{
+	return sprintf(buf, "%d\n", INT_MAX);
+}
+
+static MDEV_TYPE_ATTR_RO(available_instances);
+
+static ssize_t device_api_show(struct kobject *kobj, struct device *dev,
+			       char *buf)
+{
+	return sprintf(buf, "%s\n", VIRTIO_MDEV_DEVICE_API_STRING);
+}
+
+static MDEV_TYPE_ATTR_RO(device_api);
+
+static struct attribute *mdev_types_attrs[] = {
+	&mdev_type_attr_name.attr,
+	&mdev_type_attr_device_api.attr,
+	&mdev_type_attr_available_instances.attr,
+	NULL,
+};
+
+static struct attribute_group mdev_type_group = {
+	.name  = "virtio",
+	.attrs = mdev_types_attrs,
+};
+
+/* TBD: "vhost" type */
+
+static struct attribute_group *mdev_type_groups[] = {
+	&mdev_type_group,
+	NULL,
+};
+
+static int mvnet_set_vq_address(struct mdev_device *mdev, u16 idx,
+				u64 desc_area, u64 driver_area, u64 device_area)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+
+	vq->desc_addr = desc_area;
+	vq->driver_addr = driver_area;
+	vq->device_addr = device_area;
+
+	return 0;
+}
+
+static void mvnet_set_vq_num(struct mdev_device *mdev, u16 idx, u32 num)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+
+	vq->num = num;
+}
+
+static void mvnet_kick_vq(struct mdev_device *mdev, u16 idx)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+
+	if (vq->ready)
+		schedule_work(&mvnet->work);
+}
+
+static void mvnet_set_vq_cb(struct mdev_device *mdev, u16 idx,
+			    struct virtio_mdev_callback *cb)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+
+	vq->cb = cb->callback;
+	vq->private = cb->private;
+}
+
+static void mvnet_set_vq_ready(struct mdev_device *mdev, u16 idx, bool ready)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+
+	spin_lock(&mvnet->lock);
+	vq->ready = ready;
+	if (vq->ready)
+		mvnet_queue_ready(mvnet, idx);
+	spin_unlock(&mvnet->lock);
+}
+
+static bool mvnet_get_vq_ready(struct mdev_device *mdev, u16 idx)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+
+	return vq->ready;
+}
+
+static int mvnet_set_vq_state(struct mdev_device *mdev, u16 idx, u64 state)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+	struct vringh *vrh = &vq->vring;
+
+	spin_lock(&mvnet->lock);
+	vrh->last_avail_idx = state;
+	spin_unlock(&mvnet->lock);
+
+	return 0;
+}
+
+static u64 mvnet_get_vq_state(struct mdev_device *mdev, u16 idx)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+	struct mvnet_virtqueue *vq = &mvnet->vqs[idx];
+	struct vringh *vrh = &vq->vring;
+
+	return vrh->last_avail_idx;
+}
+
+static u16 mvnet_get_vq_align(struct mdev_device *mdev)
+{
+	return MVNET_QUEUE_ALIGN;
+}
+
+static u64 mvnet_get_features(struct mdev_device *mdev)
+{
+	return mvnet_features;
+}
+
+static int mvnet_set_features(struct mdev_device *mdev, u64 features)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+
+	/* DMA mapping must be done by driver */
+	if (!(features & (1ULL << VIRTIO_F_IOMMU_PLATFORM)))
+		return -EINVAL;
+
+	mvnet->features = features & mvnet_features;
+
+	return 0;
+}
+
+static void mvnet_set_config_cb(struct mdev_device *mdev,
+				struct virtio_mdev_callback *cb)
+{
+	/* We don't support config interrupt */
+}
+
+static u16 mvnet_get_vq_num_max(struct mdev_device *mdev)
+{
+	return MVNET_QUEUE_MAX;
+}
+
+static u32 mvnet_get_device_id(struct mdev_device *mdev)
+{
+	return MVNET_DEVICE_ID;
+}
+
+static u32 mvnet_get_vendor_id(struct mdev_device *mdev)
+{
+	return MVNET_VENDOR_ID;
+}
+
+static u8 mvnet_get_status(struct mdev_device *mdev)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+
+	return mvnet->status;
+}
+
+static void mvnet_set_status(struct mdev_device *mdev, u8 status)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+
+	mvnet->status = status;
+
+	if (status == 0) {
+		spin_lock(&mvnet->lock);
+		mvnet_reset(mvnet);
+		spin_unlock(&mvnet->lock);
+	}
+}
+
+static void mvnet_get_config(struct mdev_device *mdev, unsigned int offset,
+			     void *buf, unsigned int len)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+
+	if (offset + len < sizeof(struct virtio_net_config))
+		memcpy(buf, &mvnet->config + offset, len);
+}
+
+static void mvnet_set_config(struct mdev_device *mdev, unsigned int offset,
+			     const void *buf, unsigned int len)
+{
+	/* No writable config supportted by mvnet */
+}
+
+static u32 mvnet_get_generation(struct mdev_device *mdev)
+{
+	struct mvnet_state *mvnet = mdev_get_drvdata(mdev);
+
+	return mvnet->generation;
+}
+
+static const struct mdev_virtio_device_ops mdev_virtio_ops = {
+	.set_vq_address         = mvnet_set_vq_address,
+	.set_vq_num             = mvnet_set_vq_num,
+	.kick_vq                = mvnet_kick_vq,
+	.set_vq_cb              = mvnet_set_vq_cb,
+	.set_vq_ready           = mvnet_set_vq_ready,
+	.get_vq_ready           = mvnet_get_vq_ready,
+	.set_vq_state           = mvnet_set_vq_state,
+	.get_vq_state           = mvnet_get_vq_state,
+	.get_vq_align           = mvnet_get_vq_align,
+	.get_features           = mvnet_get_features,
+	.set_features           = mvnet_set_features,
+	.set_config_cb          = mvnet_set_config_cb,
+	.get_vq_num_max         = mvnet_get_vq_num_max,
+	.get_device_id          = mvnet_get_device_id,
+	.get_vendor_id          = mvnet_get_vendor_id,
+	.get_status             = mvnet_get_status,
+	.set_status             = mvnet_set_status,
+	.get_config             = mvnet_get_config,
+	.set_config             = mvnet_set_config,
+	.get_generation         = mvnet_get_generation,
+};
+
+static const struct mdev_parent_ops mdev_fops = {
+	.owner                  = THIS_MODULE,
+	.dev_attr_groups        = mvnet_dev_groups,
+	.mdev_attr_groups       = mdev_dev_groups,
+	.supported_type_groups  = mdev_type_groups,
+	.create                 = mvnet_create,
+	.remove			= mvnet_remove,
+};
+
+static void mvnet_device_release(struct device *dev)
+{
+	dev_dbg(dev, "mvnet: released\n");
+}
+
+static int __init mvnet_dev_init(void)
+{
+	int ret = 0;
+
+	pr_info("mvnet_dev: %s\n", __func__);
+
+	memset(&mvnet_dev, 0, sizeof(mvnet_dev));
+
+	idr_init(&mvnet_dev.vd_idr);
+
+	mvnet_dev.vd_class = class_create(THIS_MODULE, MVNET_CLASS_NAME);
+
+	if (IS_ERR(mvnet_dev.vd_class)) {
+		pr_err("Error: failed to register mvnet_dev class\n");
+		ret = PTR_ERR(mvnet_dev.vd_class);
+		goto failed1;
+	}
+
+	mvnet_dev.dev.class = mvnet_dev.vd_class;
+	mvnet_dev.dev.release = mvnet_device_release;
+	dev_set_name(&mvnet_dev.dev, "%s", MVNET_NAME);
+
+	ret = device_register(&mvnet_dev.dev);
+	if (ret)
+		goto failed2;
+
+	ret = mdev_register_device(&mvnet_dev.dev, &mdev_fops);
+	if (ret)
+		goto failed3;
+
+	mutex_init(&mdev_list_lock);
+	INIT_LIST_HEAD(&mdev_devices_list);
+
+	goto all_done;
+
+failed3:
+
+	device_unregister(&mvnet_dev.dev);
+failed2:
+	class_destroy(mvnet_dev.vd_class);
+
+failed1:
+all_done:
+	return ret;
+}
+
+static void __exit mvnet_dev_exit(void)
+{
+	mvnet_dev.dev.bus = NULL;
+	mdev_unregister_device(&mvnet_dev.dev);
+
+	device_unregister(&mvnet_dev.dev);
+	idr_destroy(&mvnet_dev.vd_idr);
+	class_destroy(mvnet_dev.vd_class);
+	mvnet_dev.vd_class = NULL;
+	pr_info("mvnet_dev: Unloaded!\n");
+}
+
+module_init(mvnet_dev_init)
+module_exit(mvnet_dev_exit)
+
+MODULE_LICENSE("GPL v2");
+MODULE_INFO(supported, "Simulate loopback ethernet device over
mdev");
+MODULE_VERSION(VERSION_STRING);
+MODULE_AUTHOR(DRIVER_AUTHOR);
-- 
2.19.1

On Thu,  7 Nov 2019 23:11:09 +0800
Jason Wang <jasowang at redhat.com> wrote:
> This sample driver creates mdev device that simulate virtio net device
> over virtio mdev transport. The device is implemented through vringh
> and workqueue. A device specific dma ops is to make sure HVA is used
> directly as the IOVA. This should be sufficient for kernel virtio
> driver to work.
> 
> Only 'virtio' type is supported right now. I plan to add
'vhost' type
> on top which requires some virtual IOMMU implemented in this sample
> driver.
> 
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  MAINTAINERS                        |   1 +
>  samples/Kconfig                    |  10 +
>  samples/vfio-mdev/Makefile         |   1 +
>  samples/vfio-mdev/mvnet_loopback.c | 687 +++++++++++++++++++++++++++++
>  4 files changed, 699 insertions(+)
>  create mode 100644 samples/vfio-mdev/mvnet_loopback.c
Acked-by: Cornelia Huck <cohuck at redhat.com>

On Thu,  7 Nov 2019 23:11:06 +0800
Jason Wang <jasowang at redhat.com> wrote:
> Currently, except for the create and remove, the rest of
> mdev_parent_ops is designed for vfio-mdev driver only and may not help
> for kernel mdev driver. With the help of class id, this patch
> introduces device specific callbacks inside mdev_device
> structure. This allows different set of callback to be used by
> vfio-mdev and virtio-mdev.
> 
> Reviewed-by: Parav Pandit <parav at mellanox.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  .../driver-api/vfio-mediated-device.rst       | 35 +++++++++----
>  MAINTAINERS                                   |  1 +
>  drivers/gpu/drm/i915/gvt/kvmgt.c              | 18 ++++---
>  drivers/s390/cio/vfio_ccw_ops.c               | 18 ++++---
>  drivers/s390/crypto/vfio_ap_ops.c             | 14 +++--
>  drivers/vfio/mdev/mdev_core.c                 | 24 ++++++++-
>  drivers/vfio/mdev/mdev_private.h              |  5 ++
>  drivers/vfio/mdev/vfio_mdev.c                 | 37 ++++++-------
>  include/linux/mdev.h                          | 43 ++++-----------
>  include/linux/mdev_vfio_ops.h                 | 52 +++++++++++++++++++
>  samples/vfio-mdev/mbochs.c                    | 20 ++++---
>  samples/vfio-mdev/mdpy.c                      | 20 ++++---
>  samples/vfio-mdev/mtty.c                      | 18 ++++---
>  13 files changed, 206 insertions(+), 99 deletions(-)
>  create mode 100644 include/linux/mdev_vfio_ops.h
You dropped my R-b :(, here it is again:

Reviewed-by: Cornelia Huck <cohuck at redhat.com>

On Thu, Nov 07, 2019 at 11:11:03PM +0800, Jason Wang
wrote:
> Hi all:
> 
> There are hardwares that can do virtio datapath offloading while
> having its own control path. This path tries to implement a mdev based
> unified API to support using kernel virtio driver to drive those
> devices. This is done by introducing a new mdev transport for virtio
> (virtio_mdev) and register itself as a new kind of mdev driver. Then
> it provides a unified way for kernel virtio driver to talk with mdev
> device implementation.
> 
> Though the series only contains kernel driver support, the goal is to
> make the transport generic enough to support userspace drivers. This
> means vhost-mdev[1] could be built on top as well by resuing the
> transport.
> 
> A sample driver is also implemented which simulate a virito-net
> loopback ethernet device on top of vringh + workqueue. This could be
> used as a reference implementation for real hardware driver.
> 
> Also a real IFC VF driver was also posted here[2] which is a good
> reference for vendors who is interested in their own virtio datapath
> offloading product.
> 
> Consider mdev framework only support VFIO device and driver right now,
> this series also extend it to support other types. This is done
> through introducing class id to the device and pairing it with
> id_talbe claimed by the driver. On top, this seris also decouple
> device specific ops out of the common ones for implementing class
> specific operations over mdev bus.
> 
> Pktgen test was done with virito-net + mvnet loop back device.
> 
> Please review.
> 
> [1] https://lkml.org/lkml/2019/11/5/424
> [2] https://lkml.org/lkml/2019/11/5/227
> 
> Changes from V10:
> - rename mvnet to mvnet_loopback
> - fix typo in the help text for sample Kconfig
Acked-by: Michael S. Tsirkin <mst at redhat.com>

> Changes from V9:
> - Tweak the help text for virito-mdev kconfig
> 
> Changes from V8:
> - try silent checkpatch, some are still there becuase they were inherited
>   from virtio_config_ops which needs to be resolved in an independent
series
> - tweak on the comment and doc
> - remove VIRTIO_MDEV_F_VERSION_1 completely
> - rename CONFIG_VIRTIO_MDEV_DEVICE to CONFIG_VIRTIO_MDEV
> 
> Changes from V7:
> - drop {set|get}_mdev_features for virtio
> - typo and comment style fixes
> 
> Changes from V6:
> - rename ops files and compile guard
> 
> Changes from V5:
> - use dev_warn() instead of WARN(1) when class id is not set
> - validate id_table before trying to do matching between device and
>   driver
> - add wildcard for modpost script
> - use unique name for id_table
> - move get_mdev_features() to be the first member of virtio_device_ops
>   and more comments for it
> - typo fixes for the comments above virtio_mdev_ops
> 
> Changes from V4:
> - keep mdev_set_class() for the device that doesn't use device ops
> - use union for device ops pointer in mdev_device
> - introduce class specific helper for getting is device ops
> - use WARN_ON instead of BUG_ON in mdev_set_virtio_ops
> - explain details of get_mdev_features() and get_vendor_id()
> - distinguish the optional virito device ops from mandatory ones and
>   make get_generation() optional
> - rename vfio_mdev.h to vfio_mdev_ops.h, rename virito_mdev.h to
>   virtio_mdev_ops.h
> - don't abuse version fileds in virtio_mdev structure, use features
>   instead
> - fix warning during device remove
> - style & docs tweaks and typo fixes
> 
> Changes from V3:
> - document that class id (device ops) must be specified in create()
> - add WARN() when trying to set class_id when it has already set
> - add WARN() when class_id is not specified in create() and correctly
>   return an error in this case
> - correct the prototype of mdev_set_class() in the doc
> - add documention of mdev_set_class()
> - remove the unnecessary "class_id_fail" label when class id is
not
>   specified in create()
> - convert id_table in vfio_mdev to const
> - move mdev_set_class and its friends after mdev_uuid()
> - suqash the patch of bus uevent into patch of introducing class id
> - tweak the words in the docs per Cornelia suggestion
> - tie class_id and device ops through class specific initialization
>   routine like mdev_set_vfio_ops()
> - typos fixes in the docs of virtio-mdev callbacks
> - document the usage of virtqueues in struct virtio_mdev_device
> - remove the useless vqs array in struct virtio_mdev_device
> - rename MDEV_ID_XXX to MDEV_CLASS_ID_XXX
> 
> Changes from V2:
> - fail when class_id is not specified
> - drop the vringh patch
> - match the doc to the code
> - tweak the commit log
> - move device_ops from parent to mdev device
> - remove the unused MDEV_ID_VHOST
> 
> Changes from V1:
> - move virtio_mdev.c to drivers/virtio
> - store class_id in mdev_device instead of mdev_parent
> - store device_ops in mdev_device instead of mdev_parent
> - reorder the patch, vringh fix comes first
> - really silent compiling warnings
> - really switch to use u16 for class_id
> - uevent and modpost support for mdev class_id
> - vraious tweaks per comments from Parav
> 
> Changes from RFC-V2:
> - silent compile warnings on some specific configuration
> - use u16 instead u8 for class id
> - reseve MDEV_ID_VHOST for future vhost-mdev work
> - introduce "virtio" type for mvnet and make "vhost"
type for future
>   work
> - add entries in MAINTAINER
> - tweak and typos fixes in commit log
> 
> Changes from RFC-V1:
> - rename device id to class id
> - add docs for class id and device specific ops (device_ops)
> - split device_ops into seperate headers
> - drop the mdev_set_dma_ops()
> - use device_ops to implement the transport API, then it's not a part
>   of UAPI any more
> - use GFP_ATOMIC in mvnet sample device and other tweaks
> - set_vring_base/get_vring_base support for mvnet device
> 
> Jason Wang (6):
>   mdev: class id support
>   modpost: add support for mdev class id
>   mdev: introduce device specific ops
>   mdev: introduce virtio device and its device ops
>   virtio: introduce a mdev based transport
>   docs: sample driver to demonstrate how to implement virtio-mdev
>     framework
> 
>  .../driver-api/vfio-mediated-device.rst       |  38 +-
>  MAINTAINERS                                   |   3 +
>  drivers/gpu/drm/i915/gvt/kvmgt.c              |  17 +-
>  drivers/s390/cio/vfio_ccw_ops.c               |  17 +-
>  drivers/s390/crypto/vfio_ap_ops.c             |  13 +-
>  drivers/vfio/mdev/mdev_core.c                 |  60 ++
>  drivers/vfio/mdev/mdev_driver.c               |  25 +
>  drivers/vfio/mdev/mdev_private.h              |   8 +
>  drivers/vfio/mdev/vfio_mdev.c                 |  45 +-
>  drivers/virtio/Kconfig                        |  13 +
>  drivers/virtio/Makefile                       |   1 +
>  drivers/virtio/virtio_mdev.c                  | 406 +++++++++++
>  include/linux/mdev.h                          |  57 +-
>  include/linux/mdev_vfio_ops.h                 |  52 ++
>  include/linux/mdev_virtio_ops.h               | 147 ++++
>  include/linux/mod_devicetable.h               |   8 +
>  samples/Kconfig                               |  10 +
>  samples/vfio-mdev/Makefile                    |   1 +
>  samples/vfio-mdev/mbochs.c                    |  19 +-
>  samples/vfio-mdev/mdpy.c                      |  19 +-
>  samples/vfio-mdev/mtty.c                      |  17 +-
>  samples/vfio-mdev/mvnet_loopback.c            | 687 ++++++++++++++++++
>  scripts/mod/devicetable-offsets.c             |   3 +
>  scripts/mod/file2alias.c                      |  11 +
>  24 files changed, 1586 insertions(+), 91 deletions(-)
>  create mode 100644 drivers/virtio/virtio_mdev.c
>  create mode 100644 include/linux/mdev_vfio_ops.h
>  create mode 100644 include/linux/mdev_virtio_ops.h
>  create mode 100644 samples/vfio-mdev/mvnet_loopback.c
> 
> -- 
> 2.19.1