Re: [RFC v3] vhost: introduce mdev based hardware vhost backend

From: Jason Wang
Date: Mon Sep 02 2019 - 00:15:24 EST


On 2019/8/28 äå1:37, Tiwei Bie wrote:
Details about this can be found here:

https://lwn.net/Articles/750770/

What's new in this version
==========================

There are three choices based on the discussion [1] in RFC v2:

#1. We expose a VFIO device, so we can reuse the VFIO container/group
based DMA API and potentially reuse a lot of VFIO code in QEMU.

But in this case, we have two choices for the VFIO device interface
(i.e. the interface on top of VFIO device fd):

A) we may invent a new vhost protocol (as demonstrated by the code
in this RFC) on VFIO device fd to make it work in VFIO's way,
i.e. regions and irqs.

B) Or as you proposed, instead of inventing a new vhost protocol,
we can reuse most existing vhost ioctls on the VFIO device fd
directly. There should be no conflicts between the VFIO ioctls
(type is 0x3B) and VHOST ioctls (type is 0xAF) currently.

#2. Instead of exposing a VFIO device, we may expose a VHOST device.
And we will introduce a new mdev driver vhost-mdev to do this.
It would be natural to reuse the existing kernel vhost interface
(ioctls) on it as much as possible. But we will need to invent
some APIs for DMA programming (reusing VHOST_SET_MEM_TABLE is a
choice, but it's too heavy and doesn't support vIOMMU by itself).
This version is more like a quick PoC to try Jason's proposal on
reusing vhost ioctls. And the second way (#1/B) in above three
choices was chosen in this version to demonstrate the idea quickly.

Now the userspace API looks like this:

- VFIO's container/group based IOMMU API is used to do the
DMA programming.

- Vhost's existing ioctls are used to setup the device.

And the device will report device_api as "vfio-vhost".

Note that, there are dirty hacks in this version. If we decide to
go this way, some refactoring in vhost.c/vhost.h may be needed.

PS. The direct mapping of the notify registers isn't implemented
in this version.

[1] https://lkml.org/lkml/2019/7/9/101


Thanks for the patch, see comments inline.



Signed-off-by: Tiwei Bie <tiwei.bie@xxxxxxxxx>
---
drivers/vhost/Kconfig | 9 +
drivers/vhost/Makefile | 3 +
drivers/vhost/mdev.c | 382 +++++++++++++++++++++++++++++++++++++
include/linux/vhost_mdev.h | 58 ++++++
include/uapi/linux/vfio.h | 2 +
include/uapi/linux/vhost.h | 8 +
6 files changed, 462 insertions(+)
create mode 100644 drivers/vhost/mdev.c
create mode 100644 include/linux/vhost_mdev.h

diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 3d03ccbd1adc..2ba54fcf43b7 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -34,6 +34,15 @@ config VHOST_VSOCK
To compile this driver as a module, choose M here: the module will be called
vhost_vsock.
+config VHOST_MDEV
+ tristate "Hardware vhost accelerator abstraction"
+ depends on EVENTFD && VFIO && VFIO_MDEV
+ select VHOST
+ default n
+ ---help---
+ Say Y here to enable the vhost_mdev module
+ for use with hardware vhost accelerators
+
config VHOST
tristate
---help---
diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile
index 6c6df24f770c..ad9c0f8c6d8c 100644
--- a/drivers/vhost/Makefile
+++ b/drivers/vhost/Makefile
@@ -10,4 +10,7 @@ vhost_vsock-y := vsock.o
obj-$(CONFIG_VHOST_RING) += vringh.o
+obj-$(CONFIG_VHOST_MDEV) += vhost_mdev.o
+vhost_mdev-y := mdev.o
+
obj-$(CONFIG_VHOST) += vhost.o
diff --git a/drivers/vhost/mdev.c b/drivers/vhost/mdev.c
new file mode 100644
index 000000000000..6bef1d9ae2e6
--- /dev/null
+++ b/drivers/vhost/mdev.c
@@ -0,0 +1,382 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2018-2019 Intel Corporation.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/vfio.h>
+#include <linux/vhost.h>
+#include <linux/mdev.h>
+#include <linux/vhost_mdev.h>
+
+#include "vhost.h"
+
+struct vhost_mdev {
+ struct vhost_dev dev;
+ bool opened;
+ int nvqs;
+ u64 state;
+ u64 acked_features;
+ u64 features;
+ const struct vhost_mdev_device_ops *ops;
+ struct mdev_device *mdev;
+ void *private;
+ struct vhost_virtqueue vqs[];
+};
+
+static void handle_vq_kick(struct vhost_work *work)
+{
+ struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
+ poll.work);
+ struct vhost_mdev *vdpa = container_of(vq->dev, struct vhost_mdev, dev);
+
+ vdpa->ops->notify(vdpa, vq - vdpa->vqs);
+}
+
+static int vhost_set_state(struct vhost_mdev *vdpa, u64 __user *statep)
+{
+ u64 state;
+
+ if (copy_from_user(&state, statep, sizeof(state)))
+ return -EFAULT;
+
+ if (state >= VHOST_MDEV_S_MAX)
+ return -EINVAL;
+
+ if (vdpa->state == state)
+ return 0;
+
+ mutex_lock(&vdpa->dev.mutex);
+
+ vdpa->state = state;
+
+ switch (vdpa->state) {
+ case VHOST_MDEV_S_RUNNING:
+ vdpa->ops->start(vdpa);
+ break;
+ case VHOST_MDEV_S_STOPPED:
+ vdpa->ops->stop(vdpa);
+ break;
+ }
+
+ mutex_unlock(&vdpa->dev.mutex);
+
+ return 0;
+}
+
+static int vhost_set_features(struct vhost_mdev *vdpa, u64 __user *featurep)
+{
+ u64 features;
+
+ if (copy_from_user(&features, featurep, sizeof(features)))
+ return -EFAULT;
+
+ if (features & ~vdpa->features)
+ return -EINVAL;
+
+ vdpa->acked_features = features;
+ vdpa->ops->features_changed(vdpa);
+ return 0;
+}
+
+static int vhost_get_features(struct vhost_mdev *vdpa, u64 __user *featurep)
+{
+ if (copy_to_user(featurep, &vdpa->features, sizeof(vdpa->features)))
+ return -EFAULT;
+ return 0;
+}
+
+static int vhost_get_vring_base(struct vhost_mdev *vdpa, void __user *argp)
+{
+ struct vhost_virtqueue *vq;
+ u32 idx;
+ int r;
+
+ r = get_user(idx, (u32 __user *)argp);
+ if (r < 0)
+ return r;
+
+ vq = &vdpa->vqs[idx];
+ vq->last_avail_idx = vdpa->ops->get_vring_base(vdpa, idx);
+
+ return vhost_vring_ioctl(&vdpa->dev, VHOST_GET_VRING_BASE, argp);
+}
+
+/*
+ * Helpers for backend to register mdev.
+ */
+
+struct vhost_mdev *vhost_mdev_alloc(struct mdev_device *mdev, void *private,
+ int nvqs)
+{
+ struct vhost_mdev *vdpa;
+ struct vhost_dev *dev;
+ struct vhost_virtqueue **vqs;
+ size_t size;
+ int i;
+
+ size = sizeof(struct vhost_mdev) + nvqs * sizeof(struct vhost_virtqueue);
+
+ vdpa = kzalloc(size, GFP_KERNEL);
+ if (!vdpa)
+ return NULL;
+
+ vdpa->nvqs = nvqs;
+
+ vqs = kmalloc_array(nvqs, sizeof(*vqs), GFP_KERNEL);
+ if (!vqs) {
+ kfree(vdpa);
+ return NULL;
+ }
+
+ dev = &vdpa->dev;
+ for (i = 0; i < nvqs; i++) {
+ vqs[i] = &vdpa->vqs[i];
+ vqs[i]->handle_kick = handle_vq_kick;
+ }
+ vhost_dev_init(dev, vqs, nvqs, 0, 0, 0);
+
+ vdpa->private = private;
+ vdpa->mdev = mdev;
+
+ mdev_set_drvdata(mdev, vdpa);
+
+ return vdpa;
+}
+EXPORT_SYMBOL(vhost_mdev_alloc);
+
+void vhost_mdev_free(struct vhost_mdev *vdpa)
+{
+ struct mdev_device *mdev;
+
+ mdev = vdpa->mdev;
+ mdev_set_drvdata(mdev, NULL);
+
+ vhost_dev_stop(&vdpa->dev);
+ vhost_dev_cleanup(&vdpa->dev);
+ kfree(vdpa->dev.vqs);
+ kfree(vdpa);
+}
+EXPORT_SYMBOL(vhost_mdev_free);
+
+ssize_t vhost_mdev_read(struct mdev_device *mdev, char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ return -EINVAL;
+}
+EXPORT_SYMBOL(vhost_mdev_read);
+
+
+ssize_t vhost_mdev_write(struct mdev_device *mdev, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ return -EINVAL;
+}
+EXPORT_SYMBOL(vhost_mdev_write);
+
+int vhost_mdev_mmap(struct mdev_device *mdev, struct vm_area_struct *vma)
+{
+ // TODO
+ return -EINVAL;
+}
+EXPORT_SYMBOL(vhost_mdev_mmap);
+
+long vhost_mdev_ioctl(struct mdev_device *mdev, unsigned int cmd,
+ unsigned long arg)
+{
+ void __user *argp = (void __user *)arg;
+ struct vhost_mdev *vdpa;
+ unsigned long minsz;
+ int ret = 0;
+
+ if (!mdev)
+ return -EINVAL;
+
+ vdpa = mdev_get_drvdata(mdev);
+ if (!vdpa)
+ return -ENODEV;
+
+ switch (cmd) {
+ case VFIO_DEVICE_GET_INFO:
+ {
+ struct vfio_device_info info;
+
+ minsz = offsetofend(struct vfio_device_info, num_irqs);
+
+ if (copy_from_user(&info, (void __user *)arg, minsz)) {
+ ret = -EFAULT;
+ break;
+ }
+
+ if (info.argsz < minsz) {
+ ret = -EINVAL;
+ break;
+ }
+
+ info.flags = VFIO_DEVICE_FLAGS_VHOST;
+ info.num_regions = 0;
+ info.num_irqs = 0;
+
+ if (copy_to_user((void __user *)arg, &info, minsz)) {
+ ret = -EFAULT;
+ break;
+ }
+
+ break;
+ }
+ case VFIO_DEVICE_GET_REGION_INFO:
+ case VFIO_DEVICE_GET_IRQ_INFO:
+ case VFIO_DEVICE_SET_IRQS:
+ case VFIO_DEVICE_RESET:
+ ret = -EINVAL;
+ break;
+
+ case VHOST_MDEV_SET_STATE:
+ ret = vhost_set_state(vdpa, argp);
+ break;


So this is used to start or stop the device. This means if userspace want to drive a network device, the API is not 100% compatible. Any blocker for this? E.g for SET_BACKEND, we can pass a fd and then identify the type of backend.

Another question is, how can user know the type of a device?


+ case VHOST_GET_FEATURES:
+ ret = vhost_get_features(vdpa, argp);
+ break;
+ case VHOST_SET_FEATURES:
+ ret = vhost_set_features(vdpa, argp);
+ break;
+ case VHOST_GET_VRING_BASE:
+ ret = vhost_get_vring_base(vdpa, argp);
+ break;
+ default:
+ ret = vhost_dev_ioctl(&vdpa->dev, cmd, argp);
+ if (ret == -ENOIOCTLCMD)
+ ret = vhost_vring_ioctl(&vdpa->dev, cmd, argp);
+ }
+
+ return ret;
+}
+EXPORT_SYMBOL(vhost_mdev_ioctl);
+
+int vhost_mdev_open(struct mdev_device *mdev)
+{
+ struct vhost_mdev *vdpa;
+ int ret = 0;
+
+ vdpa = mdev_get_drvdata(mdev);
+ if (!vdpa)
+ return -ENODEV;
+
+ mutex_lock(&vdpa->dev.mutex);
+
+ if (vdpa->opened)
+ ret = -EBUSY;
+ else
+ vdpa->opened = true;
+
+ mutex_unlock(&vdpa->dev.mutex);
+
+ return ret;
+}
+EXPORT_SYMBOL(vhost_mdev_open);
+
+void vhost_mdev_close(struct mdev_device *mdev)
+{
+ struct vhost_mdev *vdpa;
+
+ vdpa = mdev_get_drvdata(mdev);
+
+ mutex_lock(&vdpa->dev.mutex);
+
+ vhost_dev_stop(&vdpa->dev);
+ vhost_dev_cleanup(&vdpa->dev);
+
+ vdpa->opened = false;
+ mutex_unlock(&vdpa->dev.mutex);
+}
+EXPORT_SYMBOL(vhost_mdev_close);
+
+/*
+ * Helpers for backend to set/get information.
+ */
+
+int vhost_mdev_set_device_ops(struct vhost_mdev *vdpa,
+ const struct vhost_mdev_device_ops *ops)
+{
+ vdpa->ops = ops;
+ return 0;
+}
+EXPORT_SYMBOL(vhost_mdev_set_device_ops);
+
+int vhost_mdev_set_features(struct vhost_mdev *vdpa, u64 features)
+{
+ vdpa->features = features;
+ return 0;
+}
+EXPORT_SYMBOL(vhost_mdev_set_features);
+
+struct eventfd_ctx *
+vhost_mdev_get_call_ctx(struct vhost_mdev *vdpa, int queue_id)
+{
+ return vdpa->vqs[queue_id].call_ctx;
+}
+EXPORT_SYMBOL(vhost_mdev_get_call_ctx);
+
+int vhost_mdev_get_acked_features(struct vhost_mdev *vdpa, u64 *features)
+{
+ *features = vdpa->acked_features;
+ return 0;
+}
+EXPORT_SYMBOL(vhost_mdev_get_acked_features);
+
+int vhost_mdev_get_vring_num(struct vhost_mdev *vdpa, int queue_id, u16 *num)
+{
+ *num = vdpa->vqs[queue_id].num;
+ return 0;
+}
+EXPORT_SYMBOL(vhost_mdev_get_vring_num);
+
+int vhost_mdev_get_vring_base(struct vhost_mdev *vdpa, int queue_id, u16 *base)
+{
+ *base = vdpa->vqs[queue_id].last_avail_idx;
+ return 0;
+}
+EXPORT_SYMBOL(vhost_mdev_get_vring_base);
+
+int vhost_mdev_get_vring_addr(struct vhost_mdev *vdpa, int queue_id,
+ struct vhost_vring_addr *addr)
+{
+ struct vhost_virtqueue *vq = &vdpa->vqs[queue_id];
+
+ /*
+ * XXX: we need userspace to pass guest physical address or
+ * IOVA directly.
+ */
+ addr->flags = vq->log_used ? (0x1 << VHOST_VRING_F_LOG) : 0;
+ addr->desc_user_addr = (__u64)vq->desc;
+ addr->avail_user_addr = (__u64)vq->avail;
+ addr->used_user_addr = (__u64)vq->used;
+ addr->log_guest_addr = (__u64)vq->log_addr;
+ return 0;
+}
+EXPORT_SYMBOL(vhost_mdev_get_vring_addr);
+
+int vhost_mdev_get_log_base(struct vhost_mdev *vdpa, int queue_id,
+ void **log_base, u64 *log_size)
+{
+ // TODO
+ return 0;
+}
+EXPORT_SYMBOL(vhost_mdev_get_log_base);
+
+struct mdev_device *vhost_mdev_get_mdev(struct vhost_mdev *vdpa)
+{
+ return vdpa->mdev;
+}
+EXPORT_SYMBOL(vhost_mdev_get_mdev);
+
+void *vhost_mdev_get_private(struct vhost_mdev *vdpa)
+{
+ return vdpa->private;
+}
+EXPORT_SYMBOL(vhost_mdev_get_private);
+
+MODULE_VERSION("0.0.0");
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("Hardware vhost accelerator abstraction");
diff --git a/include/linux/vhost_mdev.h b/include/linux/vhost_mdev.h
new file mode 100644
index 000000000000..070787ce6b36
--- /dev/null
+++ b/include/linux/vhost_mdev.h
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2018-2019 Intel Corporation.
+ */
+
+#ifndef _VHOST_MDEV_H
+#define _VHOST_MDEV_H
+
+struct mdev_device;
+struct vhost_mdev;
+
+typedef int (*vhost_mdev_start_device_t)(struct vhost_mdev *vdpa);
+typedef int (*vhost_mdev_stop_device_t)(struct vhost_mdev *vdpa);
+typedef int (*vhost_mdev_set_features_t)(struct vhost_mdev *vdpa);
+typedef void (*vhost_mdev_notify_device_t)(struct vhost_mdev *vdpa, int queue_id);
+typedef u64 (*vhost_mdev_get_notify_addr_t)(struct vhost_mdev *vdpa, int queue_id);
+typedef u16 (*vhost_mdev_get_vring_base_t)(struct vhost_mdev *vdpa, int queue_id);
+typedef void (*vhost_mdev_features_changed_t)(struct vhost_mdev *vdpa);
+
+struct vhost_mdev_device_ops {
+ vhost_mdev_start_device_t start;
+ vhost_mdev_stop_device_t stop;
+ vhost_mdev_notify_device_t notify;
+ vhost_mdev_get_notify_addr_t get_notify_addr;
+ vhost_mdev_get_vring_base_t get_vring_base;
+ vhost_mdev_features_changed_t features_changed;
+};


Consider we want to implement a network device, who is going to implement the device configuration space? I believe it's not good to invent another set of API for doing this. So I believe we want something like read_config/write_config here.

Then I came up an idea:

1) introduce a new mdev bus transport, and a new mdev driver virtio_mdev
2) vDPA (either software or hardware) can register as a device of virtio mdev device
3) then we can use kernel virtio driver to drive vDPA device and utilize kernel networking/storage stack
4) for userspace driver like vhost-mdev, it could be built of top of mdev transport

Having a full new transport for virtio, the advantages are obvious:

1) A generic solution for both kernel and userspace driver and support configuration space access
2) For kernel driver, exist kernel networking/storage stack could be reused, and so did fast path implementation (e.g XDP, io_uring etc).
2) For userspace driver, the function of virtio transport is a superset of vhost, any API could be built on top easily (e.g vhost ioctl).

What's your thought?

Thanks


+
+struct vhost_mdev *vhost_mdev_alloc(struct mdev_device *mdev,
+ void *private, int nvqs);
+void vhost_mdev_free(struct vhost_mdev *vdpa);
+
+ssize_t vhost_mdev_read(struct mdev_device *mdev, char __user *buf,
+ size_t count, loff_t *ppos);
+ssize_t vhost_mdev_write(struct mdev_device *mdev, const char __user *buf,
+ size_t count, loff_t *ppos);
+long vhost_mdev_ioctl(struct mdev_device *mdev, unsigned int cmd,
+ unsigned long arg);
+int vhost_mdev_mmap(struct mdev_device *mdev, struct vm_area_struct *vma);
+int vhost_mdev_open(struct mdev_device *mdev);
+void vhost_mdev_close(struct mdev_device *mdev);
+
+int vhost_mdev_set_device_ops(struct vhost_mdev *vdpa,
+ const struct vhost_mdev_device_ops *ops);
+int vhost_mdev_set_features(struct vhost_mdev *vdpa, u64 features);
+struct eventfd_ctx *vhost_mdev_get_call_ctx(struct vhost_mdev *vdpa,
+ int queue_id);
+int vhost_mdev_get_acked_features(struct vhost_mdev *vdpa, u64 *features);
+int vhost_mdev_get_vring_num(struct vhost_mdev *vdpa, int queue_id, u16 *num);
+int vhost_mdev_get_vring_base(struct vhost_mdev *vdpa, int queue_id, u16 *base);
+int vhost_mdev_get_vring_addr(struct vhost_mdev *vdpa, int queue_id,
+ struct vhost_vring_addr *addr);
+int vhost_mdev_get_log_base(struct vhost_mdev *vdpa, int queue_id,
+ void **log_base, u64 *log_size);
+struct mdev_device *vhost_mdev_get_mdev(struct vhost_mdev *vdpa);
+void *vhost_mdev_get_private(struct vhost_mdev *vdpa);
+
+#endif /* _VHOST_MDEV_H */
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 8f10748dac79..0300d6831cc5 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -201,6 +201,7 @@ struct vfio_device_info {
#define VFIO_DEVICE_FLAGS_AMBA (1 << 3) /* vfio-amba device */
#define VFIO_DEVICE_FLAGS_CCW (1 << 4) /* vfio-ccw device */
#define VFIO_DEVICE_FLAGS_AP (1 << 5) /* vfio-ap device */
+#define VFIO_DEVICE_FLAGS_VHOST (1 << 6) /* vfio-vhost device */
__u32 num_regions; /* Max region index + 1 */
__u32 num_irqs; /* Max IRQ index + 1 */
};
@@ -217,6 +218,7 @@ struct vfio_device_info {
#define VFIO_DEVICE_API_AMBA_STRING "vfio-amba"
#define VFIO_DEVICE_API_CCW_STRING "vfio-ccw"
#define VFIO_DEVICE_API_AP_STRING "vfio-ap"
+#define VFIO_DEVICE_API_VHOST_STRING "vfio-vhost"
/**
* VFIO_DEVICE_GET_REGION_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 8,
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index 40d028eed645..5afbc2f08fa3 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -116,4 +116,12 @@
#define VHOST_VSOCK_SET_GUEST_CID _IOW(VHOST_VIRTIO, 0x60, __u64)
#define VHOST_VSOCK_SET_RUNNING _IOW(VHOST_VIRTIO, 0x61, int)
+/* VHOST_MDEV specific defines */
+
+#define VHOST_MDEV_SET_STATE _IOW(VHOST_VIRTIO, 0x70, __u64)
+
+#define VHOST_MDEV_S_STOPPED 0
+#define VHOST_MDEV_S_RUNNING 1
+#define VHOST_MDEV_S_MAX 2
+
#endif