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    SubjectRe: [PATCH] vhost: introduce mdev based hardware backend
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    On 2019/9/26 下午12:54, Tiwei Bie wrote:
    > This patch introduces a mdev based hardware vhost backend.
    > This backend is built on top of the same abstraction used
    > in virtio-mdev and provides a generic vhost interface for
    > userspace to accelerate the virtio devices in guest.
    >
    > This backend is implemented as a mdev device driver on top
    > of the same mdev device ops used in virtio-mdev but using
    > a different mdev class id, and it will register the device
    > as a VFIO device for userspace to use. Userspace can setup
    > the IOMMU with the existing VFIO container/group APIs and
    > then get the device fd with the device name. After getting
    > the device fd of this device, userspace can use vhost ioctls
    > to setup the backend.
    >
    > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
    > ---
    > This patch depends on below series:
    > https://lkml.org/lkml/2019/9/24/357


    Looks pretty nice, comments inline.


    >
    > RFC v4 -> v1:
    > - Implement vhost-mdev as a mdev device driver directly and
    > connect it to VFIO container/group. (Jason);
    > - Pass ring addresses as GPAs/IOVAs in vhost-mdev to avoid
    > meaningless HVA->GPA translations (Jason);
    >
    > RFC v3 -> RFC v4:
    > - Build vhost-mdev on top of the same abstraction used by
    > virtio-mdev (Jason);
    > - Introduce vhost fd and pass VFIO fd via SET_BACKEND ioctl (MST);
    >
    > RFC v2 -> RFC v3:
    > - Reuse vhost's ioctls instead of inventing a VFIO regions/irqs
    > based vhost protocol on top of vfio-mdev (Jason);
    >
    > RFC v1 -> RFC v2:
    > - Introduce a new VFIO device type to build a vhost protocol
    > on top of vfio-mdev;
    >
    > drivers/vhost/Kconfig | 9 +
    > drivers/vhost/Makefile | 3 +
    > drivers/vhost/mdev.c | 381 +++++++++++++++++++++++++++++++++++++
    > include/uapi/linux/vhost.h | 8 +
    > 4 files changed, 401 insertions(+)
    > create mode 100644 drivers/vhost/mdev.c
    >
    > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
    > index 3d03ccbd1adc..decf0be8efe9 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 "Vhost driver for Mediated devices"
    > + depends on EVENTFD && VFIO && VFIO_MDEV
    > + select VHOST
    > + default n
    > + ---help---
    > + Say M here to enable the vhost_mdev module for use with
    > + the mediated device based 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..1c12a25b86a2
    > --- /dev/null
    > +++ b/drivers/vhost/mdev.c
    > @@ -0,0 +1,381 @@
    > +// SPDX-License-Identifier: GPL-2.0
    > +/*
    > + * Copyright (C) 2018-2019 Intel Corporation.
    > + */
    > +
    > +#include <linux/compat.h>
    > +#include <linux/kernel.h>
    > +#include <linux/miscdevice.h>
    > +#include <linux/mdev.h>
    > +#include <linux/module.h>
    > +#include <linux/vfio.h>
    > +#include <linux/vhost.h>
    > +#include <linux/virtio_mdev.h>
    > +
    > +#include "vhost.h"
    > +
    > +struct vhost_mdev {
    > + /* The lock is to protect this structure. */
    > + struct mutex mutex;
    > + struct vhost_dev dev;
    > + struct vhost_virtqueue *vqs;
    > + int nvqs;
    > + u64 state;
    > + u64 features;
    > + u64 acked_features;
    > + bool opened;
    > + struct mdev_device *mdev;
    > +};
    > +
    > +static u8 mdev_get_status(struct mdev_device *mdev)
    > +{
    > + const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(mdev);
    > +
    > + return ops->get_status(mdev);
    > +}
    > +
    > +static void mdev_set_status(struct mdev_device *mdev, u8 status)
    > +{
    > + const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(mdev);
    > +
    > + return ops->set_status(mdev, status);
    > +}
    > +
    > +static void mdev_add_status(struct mdev_device *mdev, u8 status)
    > +{
    > + status |= mdev_get_status(mdev);
    > + mdev_set_status(mdev, status);
    > +}
    > +
    > +static void mdev_reset(struct mdev_device *mdev)
    > +{
    > + mdev_set_status(mdev, 0);
    > +}
    > +
    > +static void handle_vq_kick(struct vhost_work *work)
    > +{
    > + struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
    > + poll.work);
    > + struct vhost_mdev *m = container_of(vq->dev, struct vhost_mdev, dev);
    > + const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(m->mdev);
    > +
    > + ops->kick_vq(m->mdev, vq - m->vqs);
    > +}
    > +
    > +static irqreturn_t vhost_mdev_virtqueue_cb(void *private)
    > +{
    > + struct vhost_virtqueue *vq = private;
    > + struct eventfd_ctx *call_ctx = vq->call_ctx;
    > +
    > + if (call_ctx)
    > + eventfd_signal(call_ctx, 1);
    > + return IRQ_HANDLED;
    > +}
    > +
    > +static long vhost_mdev_reset(struct vhost_mdev *m)
    > +{
    > + struct mdev_device *mdev = m->mdev;
    > +
    > + mdev_reset(mdev);
    > + mdev_add_status(mdev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
    > + mdev_add_status(mdev, VIRTIO_CONFIG_S_DRIVER);
    > + return 0;
    > +}
    > +
    > +static long vhost_mdev_start(struct vhost_mdev *m)
    > +{
    > + struct mdev_device *mdev = m->mdev;
    > + const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(mdev);
    > + struct virtio_mdev_callback cb;
    > + struct vhost_virtqueue *vq;
    > + int idx;
    > +
    > + ops->set_features(mdev, m->acked_features);
    > +
    > + mdev_add_status(mdev, VIRTIO_CONFIG_S_FEATURES_OK);
    > + if (!(mdev_get_status(mdev) & VIRTIO_CONFIG_S_FEATURES_OK))
    > + goto reset;
    > +
    > + for (idx = 0; idx < m->nvqs; idx++) {
    > + vq = &m->vqs[idx];
    > +
    > + if (!vq->desc || !vq->avail || !vq->used)
    > + break;
    > +
    > + if (ops->set_vq_state(mdev, idx, vq->last_avail_idx))
    > + goto reset;


    If we do set_vq_state() in SET_VRING_BASE, we won't need this step here.


    > +
    > + /*
    > + * In vhost-mdev, userspace should pass ring addresses
    > + * in guest physical addresses when IOMMU is disabled or
    > + * IOVAs when IOMMU is enabled.
    > + */


    A question here, consider we're using noiommu mode. If guest physical
    address is passed here, how can a device use that?

    I believe you meant "host physical address" here? And it also have the
    implication that the HPA should be continuous (e.g using hugetlbfs).

    Thanks


    > + if (ops->set_vq_address(mdev, idx, (u64)vq->desc,
    > + (u64)vq->avail, (u64)vq->used))
    > + goto reset;
    > +
    > + ops->set_vq_num(mdev, idx, vq->num);
    > +
    > + cb.callback = vhost_mdev_virtqueue_cb;
    > + cb.private = vq;
    > + ops->set_vq_cb(mdev, idx, &cb);
    > +
    > + ops->set_vq_ready(mdev, idx, 1);
    > + }
    > +
    > + mdev_add_status(mdev, VIRTIO_CONFIG_S_DRIVER_OK);
    > + if (mdev_get_status(mdev) & VIRTIO_CONFIG_S_NEEDS_RESET)
    > + goto reset;
    > + return 0;
    > +
    > +reset:
    > + vhost_mdev_reset(m);
    > + return -ENODEV;
    > +}
    > +
    > +static long vhost_set_state(struct vhost_mdev *m, u64 __user *statep)
    > +{
    > + u64 state;
    > + long r;
    > +
    > + if (copy_from_user(&state, statep, sizeof(state)))
    > + return -EFAULT;
    > +
    > + if (state >= VHOST_MDEV_S_MAX)
    > + return -EINVAL;
    > +
    > + if (m->state == state)
    > + return 0;
    > +
    > + m->state = state;
    > +
    > + switch (m->state) {
    > + case VHOST_MDEV_S_RUNNING:
    > + r = vhost_mdev_start(m);
    > + break;
    > + case VHOST_MDEV_S_STOPPED:
    > + r = vhost_mdev_reset(m);
    > + break;
    > + default:
    > + r = -EINVAL;
    > + break;
    > + }
    > +
    > + return r;
    > +}
    > +
    > +static long vhost_get_features(struct vhost_mdev *m, u64 __user *featurep)
    > +{
    > + if (copy_to_user(featurep, &m->features, sizeof(m->features)))
    > + return -EFAULT;
    > + return 0;
    > +}
    > +
    > +static long vhost_set_features(struct vhost_mdev *m, u64 __user *featurep)
    > +{
    > + u64 features;
    > +
    > + if (copy_from_user(&features, featurep, sizeof(features)))
    > + return -EFAULT;
    > +
    > + if (features & ~m->features)
    > + return -EINVAL;
    > +
    > + m->acked_features = features;
    > +
    > + return 0;
    > +}
    > +
    > +static long vhost_get_vring_base(struct vhost_mdev *m, void __user *argp)
    > +{
    > + const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(m->mdev);
    > + struct vhost_virtqueue *vq;
    > + u32 idx;
    > + long r;
    > +
    > + r = get_user(idx, (u32 __user *)argp);
    > + if (r < 0)
    > + return r;
    > + if (idx >= m->nvqs)
    > + return -ENOBUFS;
    > +
    > + vq = &m->vqs[idx];
    > + vq->last_avail_idx = ops->get_vq_state(m->mdev, idx);
    > +
    > + return vhost_vring_ioctl(&m->dev, VHOST_GET_VRING_BASE, argp);
    > +}
    > +
    > +static int vhost_mdev_open(void *device_data)
    > +{
    > + struct vhost_mdev *m = device_data;
    > + struct vhost_dev *dev;
    > + struct vhost_virtqueue **vqs;
    > + int nvqs, i, r;
    > +
    > + if (!try_module_get(THIS_MODULE))
    > + return -ENODEV;
    > +
    > + mutex_lock(&m->mutex);
    > +
    > + if (m->opened) {
    > + r = -EBUSY;
    > + goto err;
    > + }
    > +
    > + nvqs = m->nvqs;
    > + vhost_mdev_reset(m);
    > +
    > + memset(&m->dev, 0, sizeof(m->dev));
    > + memset(m->vqs, 0, nvqs * sizeof(struct vhost_virtqueue));
    > +
    > + vqs = kmalloc_array(nvqs, sizeof(*vqs), GFP_KERNEL);
    > + if (!vqs) {
    > + r = -ENOMEM;
    > + goto err;
    > + }
    > +
    > + dev = &m->dev;
    > + for (i = 0; i < nvqs; i++) {
    > + vqs[i] = &m->vqs[i];
    > + vqs[i]->handle_kick = handle_vq_kick;
    > + }
    > + vhost_dev_init(dev, vqs, nvqs, 0, 0, 0);
    > + m->opened = true;
    > + mutex_unlock(&m->mutex);
    > +
    > + return 0;
    > +
    > +err:
    > + mutex_unlock(&m->mutex);
    > + module_put(THIS_MODULE);
    > + return r;
    > +}
    > +
    > +static void vhost_mdev_release(void *device_data)
    > +{
    > + struct vhost_mdev *m = device_data;
    > +
    > + mutex_lock(&m->mutex);
    > + vhost_mdev_reset(m);
    > + vhost_dev_stop(&m->dev);
    > + vhost_dev_cleanup(&m->dev);
    > +
    > + kfree(m->dev.vqs);
    > + m->opened = false;
    > + mutex_unlock(&m->mutex);
    > + module_put(THIS_MODULE);
    > +}
    > +
    > +static long vhost_mdev_unlocked_ioctl(void *device_data,
    > + unsigned int cmd, unsigned long arg)
    > +{
    > + struct vhost_mdev *m = device_data;
    > + void __user *argp = (void __user *)arg;
    > + long r;
    > +
    > + mutex_lock(&m->mutex);
    > +
    > + switch (cmd) {
    > + case VHOST_MDEV_SET_STATE:
    > + r = vhost_set_state(m, argp);
    > + break;
    > + case VHOST_GET_FEATURES:
    > + r = vhost_get_features(m, argp);
    > + break;
    > + case VHOST_SET_FEATURES:
    > + r = vhost_set_features(m, argp);
    > + break;
    > + case VHOST_GET_VRING_BASE:
    > + r = vhost_get_vring_base(m, argp);
    > + break;


    Does it mean the SET_VRING_BASE may only take affect after
    VHOST_MEV_SET_STATE?


    > + default:
    > + r = vhost_dev_ioctl(&m->dev, cmd, argp);
    > + if (r == -ENOIOCTLCMD)
    > + r = vhost_vring_ioctl(&m->dev, cmd, argp);
    > + }
    > +
    > + mutex_unlock(&m->mutex);
    > + return r;
    > +}
    > +
    > +static const struct vfio_device_ops vfio_vhost_mdev_dev_ops = {
    > + .name = "vfio-vhost-mdev",
    > + .open = vhost_mdev_open,
    > + .release = vhost_mdev_release,
    > + .ioctl = vhost_mdev_unlocked_ioctl,
    > +};
    > +
    > +static int vhost_mdev_probe(struct device *dev)
    > +{
    > + struct mdev_device *mdev = mdev_from_dev(dev);
    > + const struct virtio_mdev_device_ops *ops = mdev_get_dev_ops(mdev);
    > + struct vhost_mdev *m;
    > + int nvqs, r;
    > +
    > + m = kzalloc(sizeof(*m), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
    > + if (!m)
    > + return -ENOMEM;
    > +
    > + mutex_init(&m->mutex);
    > +
    > + nvqs = ops->get_queue_max(mdev);
    > + m->nvqs = nvqs;


    The name could be confusing, get_queue_max() is to get the maximum
    number of entries for a virtqueue supported by this device.

    It looks to me that we need another API to query the maximum number of
    virtqueues supported by the device.

    Thanks


    > +
    > + m->vqs = kmalloc_array(nvqs, sizeof(struct vhost_virtqueue),
    > + GFP_KERNEL);
    > + if (!m->vqs) {
    > + r = -ENOMEM;
    > + goto err;
    > + }
    > +
    > + r = vfio_add_group_dev(dev, &vfio_vhost_mdev_dev_ops, m);
    > + if (r)
    > + goto err;
    > +
    > + m->features = ops->get_features(mdev);
    > + m->mdev = mdev;
    > + return 0;
    > +
    > +err:
    > + kfree(m->vqs);
    > + kfree(m);
    > + return r;
    > +}
    > +
    > +static void vhost_mdev_remove(struct device *dev)
    > +{
    > + struct vhost_mdev *m;
    > +
    > + m = vfio_del_group_dev(dev);
    > + mutex_destroy(&m->mutex);
    > + kfree(m->vqs);
    > + kfree(m);
    > +}
    > +
    > +static struct mdev_class_id id_table[] = {
    > + { MDEV_ID_VHOST },
    > + { 0 },
    > +};
    > +
    > +static struct mdev_driver vhost_mdev_driver = {
    > + .name = "vhost_mdev",
    > + .probe = vhost_mdev_probe,
    > + .remove = vhost_mdev_remove,
    > + .id_table = id_table,
    > +};
    > +
    > +static int __init vhost_mdev_init(void)
    > +{
    > + return mdev_register_driver(&vhost_mdev_driver, THIS_MODULE);
    > +}
    > +module_init(vhost_mdev_init);
    > +
    > +static void __exit vhost_mdev_exit(void)
    > +{
    > + mdev_unregister_driver(&vhost_mdev_driver);
    > +}
    > +module_exit(vhost_mdev_exit);
    > +
    > +MODULE_VERSION("0.0.1");
    > +MODULE_LICENSE("GPL v2");
    > +MODULE_DESCRIPTION("Mediated device based accelerator for virtio");
    > 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

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      Last update: 2019-09-27 05:46    [W:5.003 / U:0.340 seconds]
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