[PATCH V12 5/6] virtio: introduce a mdev based transport

[Jason Wang]

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
bus_ops of mdev parent.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/virtio/Kconfig       |  13 ++
 drivers/virtio/Makefile      |   1 +
 drivers/virtio/virtio_mdev.c | 409 +++++++++++++++++++++++++++++++++++
 include/linux/mdev_virtio.h  |   5 +
 4 files changed, 428 insertions(+)
 create mode 100644 drivers/virtio/virtio_mdev.c

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 078615cf2afc..6a89b3de97d3 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 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..7fdb42f055df
--- /dev/null
+++ b/drivers/virtio/virtio_mdev.c
@@ -0,0 +1,409 @@
+// 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@xxxxxxxxxx>
+ *
+ */
+
+#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/virtio.h>
+#include <linux/mdev_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_ops *ops = mdev_virtio_get_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_virtio_from_dev(dev);
+	const struct mdev_virtio_ops *ops = mdev_virtio_get_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_virtio_class_id virtio_id_table[] = {
+	{ MDEV_VIRTIO_CLASS_ID_VIRTIO },
+	{ 0 },
+};
+
+MODULE_DEVICE_TABLE(mdev_virtio, virtio_id_table);
+
+static struct mdev_virtio_driver virtio_mdev_driver = {
+	.drv = {
+		.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.drv, THIS_MODULE,
+				    &mdev_virtio_bus_type);
+}
+
+static void __exit virtio_mdev_exit(void)
+{
+	mdev_unregister_driver(&virtio_mdev_driver.drv);
+}
+
+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);
diff --git a/include/linux/mdev_virtio.h b/include/linux/mdev_virtio.h
index ef2dbb6c383a..5f75f3cf59e1 100644
--- a/include/linux/mdev_virtio.h
+++ b/include/linux/mdev_virtio.h
@@ -25,6 +25,11 @@ struct virtio_mdev_callback {
 	void *private;
 };
 
+enum {
+	MDEV_VIRTIO_CLASS_ID_VIRTIO = 1,
+	/* New entries must be added here */
+};
+
 /**
  * struct mdev_virtio_device_ops - Structure to be registered for each
  * mdev device to register the device for virtio/vhost drivers.
-- 
2.19.1