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

[Viktor Prutyanov <viktor@daynix.com>]

On Tue, Mar 21, 2023 at 12:23 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Tue, Mar 21, 2023 at 02:21:15AM +0300, Viktor Prutyanov wrote:
> > According to VirtIO spec v1.2, VIRTIO_F_NOTIFICATION_DATA feature
> > indicates that the driver passes extra data along with the queue
> > notifications.
> >
> > In a split queue case, the extra data is 16-bit available index. In a
> > packed queue case, the extra data is 1-bit wrap counter and 15-bit
> > available index.
> >
> > Add support for this feature for MMIO and PCI transports. Channel I/O
> > transport will not accept this feature.
> >
> > Signed-off-by: Viktor Prutyanov <viktor@daynix.com>
> > ---
> >
> >  v2: reject the feature in virtio_ccw, replace __le32 with u32
> >
> >  drivers/s390/virtio/virtio_ccw.c   |  4 +---
> >  drivers/virtio/virtio_mmio.c       | 15 ++++++++++++++-
> >  drivers/virtio/virtio_pci_common.c | 10 ++++++++++
> >  drivers/virtio/virtio_pci_common.h |  4 ++++
> >  drivers/virtio/virtio_pci_legacy.c |  2 +-
> >  drivers/virtio/virtio_pci_modern.c |  2 +-
> >  drivers/virtio/virtio_ring.c       | 17 +++++++++++++++++
> >  include/linux/virtio_ring.h        |  2 ++
> >  include/uapi/linux/virtio_config.h |  6 ++++++
> >  9 files changed, 56 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> > index a10dbe632ef9..d72a59415527 100644
> > --- a/drivers/s390/virtio/virtio_ccw.c
> > +++ b/drivers/s390/virtio/virtio_ccw.c
> > @@ -789,9 +789,7 @@ static u64 virtio_ccw_get_features(struct virtio_device *vdev)
> >
> >  static void ccw_transport_features(struct virtio_device *vdev)
> >  {
> > -     /*
> > -      * Currently nothing to do here.
> > -      */
> > +     __virtio_clear_bit(vdev, VIRTIO_F_NOTIFICATION_DATA);
> >  }
> >
> >  static int virtio_ccw_finalize_features(struct virtio_device *vdev)
> > diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> > index 3ff746e3f24a..0e13da17fe0a 100644
> > --- a/drivers/virtio/virtio_mmio.c
> > +++ b/drivers/virtio/virtio_mmio.c
> > @@ -285,6 +285,19 @@ static bool vm_notify(struct virtqueue *vq)
> >       return true;
> >  }
> >
> > +static bool vm_notify_with_data(struct virtqueue *vq)
> > +{
> > +     struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vq->vdev);
> > +     u32 data = vring_fill_notification_data(vq);
> > +
> > +     writel(data, vm_dev->base + VIRTIO_MMIO_QUEUE_NOTIFY);
> > +
> > +     return true;
> > +}
> > +
> > +#define VM_NOTIFY(vdev) (__virtio_test_bit((vdev), VIRTIO_F_NOTIFICATION_DATA) \
> > +     ? vm_notify_with_data : vm_notify)
> > +
> >  /* Notify all virtqueues on an interrupt. */
> >  static irqreturn_t vm_interrupt(int irq, void *opaque)
> >  {
> > @@ -397,7 +410,7 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned int in
> >
> >       /* Create the vring */
> >       vq = vring_create_virtqueue(index, num, VIRTIO_MMIO_VRING_ALIGN, vdev,
> > -                              true, true, ctx, vm_notify, callback, name);
> > +                     true, true, ctx, VM_NOTIFY(vdev), callback, name);
>
> I don't see why is this macro useful.
>
>
>
> >       if (!vq) {
> >               err = -ENOMEM;
> >               goto error_new_virtqueue;
> > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> > index a6c86f916dbd..535263abc2bd 100644
> > --- a/drivers/virtio/virtio_pci_common.c
> > +++ b/drivers/virtio/virtio_pci_common.c
> > @@ -43,6 +43,16 @@ bool vp_notify(struct virtqueue *vq)
> >       /* we write the queue's selector into the notification register to
> >        * signal the other end */
> >       iowrite16(vq->index, (void __iomem *)vq->priv);
> > +
> > +     return true;
> > +}
> > +
> > +bool vp_notify_with_data(struct virtqueue *vq)
> > +{
> > +     u32 data = vring_fill_notification_data(vq);
> > +
> > +     iowrite32(data, (void __iomem *)vq->priv);
> > +
> >       return true;
> >  }
> >
> > diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h
> > index 23112d84218f..9a7212dcbb32 100644
> > --- a/drivers/virtio/virtio_pci_common.h
> > +++ b/drivers/virtio/virtio_pci_common.h
> > @@ -105,6 +105,7 @@ static struct virtio_pci_device *to_vp_device(struct virtio_device *vdev)
> >  void vp_synchronize_vectors(struct virtio_device *vdev);
> >  /* the notify function used when creating a virt queue */
> >  bool vp_notify(struct virtqueue *vq);
> > +bool vp_notify_with_data(struct virtqueue *vq);
> >  /* the config->del_vqs() implementation */
> >  void vp_del_vqs(struct virtio_device *vdev);
> >  /* the config->find_vqs() implementation */
> > @@ -114,6 +115,9 @@ int vp_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
> >               struct irq_affinity *desc);
> >  const char *vp_bus_name(struct virtio_device *vdev);
> >
> > +#define VP_NOTIFY(vdev) (__virtio_test_bit((vdev), VIRTIO_F_NOTIFICATION_DATA) \
> > +     ? vp_notify : vp_notify_with_data)
> > +
> >  /* Setup the affinity for a virtqueue:
> >   * - force the affinity for per vq vector
> >   * - OR over all affinities for shared MSI
> > diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
> > index 2257f1b3d8ae..b98e994cae48 100644
> > --- a/drivers/virtio/virtio_pci_legacy.c
> > +++ b/drivers/virtio/virtio_pci_legacy.c
> > @@ -131,7 +131,7 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
> >       vq = vring_create_virtqueue(index, num,
> >                                   VIRTIO_PCI_VRING_ALIGN, &vp_dev->vdev,
> >                                   true, false, ctx,
> > -                                 vp_notify, callback, name);
> > +                                 VP_NOTIFY(&vp_dev->vdev), callback, name);
> >       if (!vq)
> >               return ERR_PTR(-ENOMEM);
> >
> > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> > index 9e496e288cfa..7fcd8af5af7e 100644
> > --- a/drivers/virtio/virtio_pci_modern.c
> > +++ b/drivers/virtio/virtio_pci_modern.c
> > @@ -321,7 +321,7 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
> >       vq = vring_create_virtqueue(index, num,
> >                                   SMP_CACHE_BYTES, &vp_dev->vdev,
> >                                   true, true, ctx,
> > -                                 vp_notify, callback, name);
> > +                                 VP_NOTIFY(&vp_dev->vdev), callback, name);
> >       if (!vq)
> >               return ERR_PTR(-ENOMEM);
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 723c4e29e1d3..5e9e1800bb6e 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -2699,6 +2699,21 @@ void vring_del_virtqueue(struct virtqueue *_vq)
> >  }
> >  EXPORT_SYMBOL_GPL(vring_del_virtqueue);
> >
> > +u32 vring_fill_notification_data(struct virtqueue *_vq)
> > +{
> > +     struct vring_virtqueue *vq = to_vvq(_vq);
> > +     u16 next;
> > +
> > +     if (vq->packed_ring)
> > +             next = (vq->packed.next_avail_idx & ~(1 << 15)) |
> > +                     ((u16)vq->packed.avail_wrap_counter << 15);
>
> I don't think the cast is needed. Neither is () around << the second <<
> here (first is needed because gcc chooses to complain: apparently it
> considers bitwise and a math operation for some obscure reason).
>
> > +     else
> > +             next = virtio16_to_cpu(_vq->vdev, vq->split.vring.avail->idx);
> > +
> > +     return ((u32)next << 16) | _vq->index;
>
> I don't think the cast is needed. Neither is () around << needed.
>
> > +}
> > +EXPORT_SYMBOL_GPL(vring_fill_notification_data);
> > +
>
> I'd inline this - it's on data path ...

As far as I see, to be inlined in virtio_mmio.c, virtio_pci_common.c
and virtio_ccw.c, the function should be defined in some header, but
definitions such as vring_virtqueue, vring_virtqueue_split,
vring_virtqueue_packed will not be available, because they are in
virtio_ring.c. Looks like, they must be moved to a separate header
in this case, isn't it?

>
> >  /* Manipulates transport-specific feature bits. */
> >  void vring_transport_features(struct virtio_device *vdev)
> >  {
>
> > @@ -2718,6 +2733,8 @@ void vring_transport_features(struct virtio_device *vdev)
> >                       break;
> >               case VIRTIO_F_ORDER_PLATFORM:
> >                       break;
> > +             case VIRTIO_F_NOTIFICATION_DATA:
> > +                     break;
> >               default:
> >                       /* We don't understand this bit. */
> >                       __virtio_clear_bit(vdev, i);
> > diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> > index 8b8af1a38991..1f65d2f77012 100644
> > --- a/include/linux/virtio_ring.h
> > +++ b/include/linux/virtio_ring.h
> > @@ -101,4 +101,6 @@ void vring_del_virtqueue(struct virtqueue *vq);
> >  void vring_transport_features(struct virtio_device *vdev);
> >
> >  irqreturn_t vring_interrupt(int irq, void *_vq);
> > +
> > +u32 vring_fill_notification_data(struct virtqueue *_vq);
> >  #endif /* _LINUX_VIRTIO_RING_H */
> > diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
> > index 3c05162bc988..2c712c654165 100644
> > --- a/include/uapi/linux/virtio_config.h
> > +++ b/include/uapi/linux/virtio_config.h
> > @@ -99,6 +99,12 @@
> >   */
> >  #define VIRTIO_F_SR_IOV                      37
> >
> > +/*
> > + * This feature indicates that the driver passes extra data (besides
> > + * identifying the virtqueue) in its device notifications.
> > + */
> > +#define VIRTIO_F_NOTIFICATION_DATA   38
> > +
> >  /*
> >   * This feature indicates that the driver can reset a queue individually.
> >   */
> > --
> > 2.35.1
>