linux-kernel - Re: [PATCH v2] virtio: add VIRTIO_F_NOTIFICATION

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Date:   Tue, 21 Mar 2023 12:00:42 +0300
From:   Viktor Prutyanov <viktor@...nix.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, cohuck@...hat.com, pasic@...ux.ibm.com,
        farman@...ux.ibm.com, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, yan@...nix.com
Subject: Re: [PATCH v2] virtio: add VIRTIO_F_NOTIFICATION_DATA feature support

On Tue, Mar 21, 2023 at 5:29 AM Jason Wang <jasowang@...hat.com> wrote:
>
> On Tue, Mar 21, 2023 at 7:21 AM Viktor Prutyanov <viktor@...nix.com> 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@...nix.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);
>
> Is there any restriction that prevents us from implementing
> VIRTIO_F_NOTIFICATION_DATA? (Spec seems doesn't limit us from this)

Most likely, nothing.

>
> >  }
> >
> >  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);
>
> Can we move this to the initialization?

This data is new for each notification, because it helps to identify
the next available index.

>
> Thanks
>

Thanks,
Viktor Prutyanov