Subject: Re: [PATCH v4] vhost: introduce mdev based hardware backend

From: Tiwei Bie <[email-masked]>
Date: Fri, 1 Nov 2019 21:56:28 +0800

On Fri, Nov 01, 2019 at 03:17:39PM +0800, Jason Wang wrote:
> On 2019/10/31 下午10:01, 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 <[email-masked]>
> > ---
> > This patch depends on below series:
> > https://lkml.org/lkml/2019/10/30/62
> > 
> > v3 -> v4:
> > - Rebase on top of virtio-mdev series v6;
> > - Some minor tweaks and improvements;
> > 
> > v2 -> v3:
> > - Fix the return value (Jason);
> > - Don't cache unnecessary information in vhost-mdev (Jason);
> > - Get rid of the memset in open (Jason);
> > - Add comments for VHOST_SET_MEM_TABLE, ... (Jason);
> > - Filter out unsupported features in vhost-mdev (Jason);
> > - Add _GET_DEVICE_ID ioctl (Jason);
> > - Add _GET_CONFIG/_SET_CONFIG ioctls (Jason);
> > - Drop _GET_QUEUE_NUM ioctl (Jason);
> > - Fix the copy-paste errors in _IOW/_IOR usage;
> > - Some minor fixes and improvements;
> > 
> > v1 -> v2:
> > - Replace _SET_STATE with _SET_STATUS (MST);
> > - Check status bits at each step (MST);
> > - Report the max ring size and max number of queues (MST);
> > - Add missing MODULE_DEVICE_TABLE (Jason);
> > - Only support the network backend w/o multiqueue for now;
> > - Some minor fixes and improvements;
> > - Rebase on top of virtio-mdev series v4;
> > 
> > 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/vfio/mdev/mdev_core.c    |  20 ++
> >   drivers/vfio/mdev/mdev_private.h |   1 +
> >   drivers/vhost/Kconfig            |  12 +
> >   drivers/vhost/Makefile           |   3 +
> >   drivers/vhost/mdev.c             | 556 +++++++++++++++++++++++++++++++
> >   include/linux/mdev.h             |   5 +
> >   include/uapi/linux/vhost.h       |  18 +
> >   include/uapi/linux/vhost_types.h |   8 +
> >   8 files changed, 623 insertions(+)
> >   create mode 100644 drivers/vhost/mdev.c
> > 
> > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> > index 22ca589750d8..109dbac01a8f 100644
> > --- a/drivers/vfio/mdev/mdev_core.c
> > +++ b/drivers/vfio/mdev/mdev_core.c
> > @@ -96,6 +96,26 @@ mdev_get_virtio_ops(struct mdev_device *mdev)
> >   }
> >   EXPORT_SYMBOL(mdev_get_virtio_ops);
> > +/* Specify the vhost device ops for the mdev device, this
> > + * must be called during create() callback for vhost mdev device.
> > + */
> > +void mdev_set_vhost_ops(struct mdev_device *mdev,
> > +			const struct virtio_mdev_device_ops *vhost_ops)
> > +{
> > +	mdev_set_class(mdev, MDEV_CLASS_ID_VHOST);
> > +	mdev->vhost_ops = vhost_ops;
> > +}
> > +EXPORT_SYMBOL(mdev_set_vhost_ops);
> > +
> > +/* Get the vhost device ops for the mdev device. */
> > +const struct virtio_mdev_device_ops *
> > +mdev_get_vhost_ops(struct mdev_device *mdev)
> > +{
> > +	WARN_ON(mdev->class_id != MDEV_CLASS_ID_VHOST);
> > +	return mdev->vhost_ops;
> > +}
> > +EXPORT_SYMBOL(mdev_get_vhost_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 7b47890c34e7..5597c846e52f 100644
> > --- a/drivers/vfio/mdev/mdev_private.h
> > +++ b/drivers/vfio/mdev/mdev_private.h
> > @@ -40,6 +40,7 @@ struct mdev_device {
> >   	union {
> >   		const struct vfio_mdev_device_ops *vfio_ops;
> >   		const struct virtio_mdev_device_ops *virtio_ops;
> > +		const struct virtio_mdev_device_ops *vhost_ops;
> 
> 
> Any reason why virtio_ops is not used for vhost here?

I don't have a strong opinion on this.
Will use virtio_ops directly.

> Other looks good.

Thanks!

> Thanks