Re: [PATCH v2] virtio-vdpa: add VIRTIO_F_NOTIFICATION_DATA feature support

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 11, 2023 at 01:25:53PM +0800, Jason Wang wrote:
> On Sun, Apr 9, 2023 at 3:07 PM Alvaro Karsz <alvaro.karsz@solid-run.com> wrote:
> >
> > Add VIRTIO_F_NOTIFICATION_DATA support for vDPA transport.
> > If this feature is negotiated, the driver passes extra data when kicking
> > a virtqueue.
> >
> > A device that offers this feature needs to implement the
> > kick_vq_with_data callback.
> >
> > kick_vq_with_data receives the vDPA device and data.
> > data includes:
> > 16 bits vqn and 16 bits next available index for split virtqueues.
> > 16 bits vqs, 15 least significant bits of next available index
> > and 1 bit next_wrap for packed virtqueues.
> >
> > This patch follows a patch [1] by Viktor Prutyanov which adds support
> > for the MMIO, channel I/O and modern PCI transports.
> >
> > This patch needs to be applied on top of Viktor's patch.
> >
> > [1] https://lore.kernel.org/lkml/20230324195029.2410503-1-viktor@daynix.com/
> >
> > Signed-off-by: Alvaro Karsz <alvaro.karsz@solid-run.com>
> > ---
> > v2:
> >         - clear the feature bit if kick_vq_with_data is not implemented.
> >         - Fix kick_vq_with_data comment in include/linux/vdpa.h
> >         - Write in more detail about the extra data in the commit log
> >
> >  drivers/virtio/virtio_vdpa.c | 23 +++++++++++++++++++++--
> >  include/linux/vdpa.h         |  9 +++++++++
> >  2 files changed, 30 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> > index d7f5af62dda..737c1f36d32 100644
> > --- a/drivers/virtio/virtio_vdpa.c
> > +++ b/drivers/virtio/virtio_vdpa.c
> > @@ -112,6 +112,17 @@ static bool virtio_vdpa_notify(struct virtqueue *vq)
> >         return true;
> >  }
> >
> > +static bool virtio_vdpa_notify_with_data(struct virtqueue *vq)
> > +{
> > +       struct vdpa_device *vdpa = vd_get_vdpa(vq->vdev);
> > +       const struct vdpa_config_ops *ops = vdpa->config;
> > +       u32 data = vring_notification_data(vq);
> > +
> > +       ops->kick_vq_with_data(vdpa, data);
> > +
> > +       return true;
> > +}
> > +
> >  static irqreturn_t virtio_vdpa_config_cb(void *private)
> >  {
> >         struct virtio_vdpa_device *vd_dev = private;
> > @@ -138,6 +149,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> >         struct device *dma_dev;
> >         const struct vdpa_config_ops *ops = vdpa->config;
> >         struct virtio_vdpa_vq_info *info;
> > +       bool (*notify)(struct virtqueue *vq) = virtio_vdpa_notify;
> >         struct vdpa_callback cb;
> >         struct virtqueue *vq;
> >         u64 desc_addr, driver_addr, device_addr;
> > @@ -154,6 +166,14 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> >         if (index >= vdpa->nvqs)
> >                 return ERR_PTR(-ENOENT);
> >
> > +       /* We cannot accept VIRTIO_F_NOTIFICATION_DATA without kick_vq_with_data */
> > +       if (__virtio_test_bit(vdev, VIRTIO_F_NOTIFICATION_DATA)) {
> > +               if (ops->kick_vq_with_data)
> > +                       notify = virtio_vdpa_notify_with_data;
> > +               else
> 
> If we do this, I wonder if we need to fail or at least warn in this case.
> 
> Thanks

Nope.  Either device can work without VIRTIO_F_NOTIFICATION_DATA
and then all is well or it can't and then it will fail FEATURES_OK.

If drivers start failing when seeing new features we'll never
be able to extend virtio again.
Same for warns, some people run with panic on warn.



> > +                       __virtio_clear_bit(vdev, VIRTIO_F_NOTIFICATION_DATA);
> > +       }
> > +
> >         /* Queue shouldn't already be set up. */
> >         if (ops->get_vq_ready(vdpa, index))
> >                 return ERR_PTR(-ENOENT);
> > @@ -183,8 +203,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> >                 dma_dev = vdpa_get_dma_dev(vdpa);
> >         vq = vring_create_virtqueue_dma(index, max_num, align, vdev,
> >                                         true, may_reduce_num, ctx,
> > -                                       virtio_vdpa_notify, callback,
> > -                                       name, dma_dev);
> > +                                       notify, callback, name, dma_dev);
> >         if (!vq) {
> >                 err = -ENOMEM;
> >                 goto error_new_virtqueue;
> > diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> > index 43f59ef10cc..04cdaad77dd 100644
> > --- a/include/linux/vdpa.h
> > +++ b/include/linux/vdpa.h
> > @@ -143,6 +143,14 @@ struct vdpa_map_file {
> >   * @kick_vq:                   Kick the virtqueue
> >   *                             @vdev: vdpa device
> >   *                             @idx: virtqueue index
> > + * @kick_vq_with_data:         Kick the virtqueue and supply extra data
> > + *                             (only if VIRTIO_F_NOTIFICATION_DATA is negotiated)
> > + *                             @vdev: vdpa device
> > + *                             @data for split virtqueue:
> > + *                             16 bits vqn and 16 bits next available index.
> > + *                             @data for packed virtqueue:
> > + *                             16 bits vqn, 15 least significant bits of
> > + *                             next available index and 1 bit next_wrap.
> >   * @set_vq_cb:                 Set the interrupt callback function for
> >   *                             a virtqueue
> >   *                             @vdev: vdpa device
> > @@ -300,6 +308,7 @@ struct vdpa_config_ops {
> >                               u64 device_area);
> >         void (*set_vq_num)(struct vdpa_device *vdev, u16 idx, u32 num);
> >         void (*kick_vq)(struct vdpa_device *vdev, u16 idx);
> > +       void (*kick_vq_with_data)(struct vdpa_device *vdev, u32 data);
> >         void (*set_vq_cb)(struct vdpa_device *vdev, u16 idx,
> >                           struct vdpa_callback *cb);
> >         void (*set_vq_ready)(struct vdpa_device *vdev, u16 idx, bool ready);
> > --
> > 2.34.1
> >

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