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Date:   Fri, 24 Mar 2023 05:07:11 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Viktor Prutyanov <viktor@daynix.com>
Cc:     Jason Wang <jasowang@redhat.com>, cohuck@redhat.com,
        pasic@linux.ibm.com, farman@linux.ibm.com,
        linux-s390@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, yan@daynix.com
Subject: Re: [PATCH v5] virtio: add VIRTIO_F_NOTIFICATION_DATA feature support
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References: <20230323085551.2346411-1-viktor@daynix.com>
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On Fri, Mar 24, 2023 at 10:44:23AM +0300, Viktor Prutyanov wrote:
> On Fri, Mar 24, 2023 at 8:31 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Fri, Mar 24, 2023 at 11:09:19AM +0800, Jason Wang wrote:
> > > On Thu, Mar 23, 2023 at 4:56 PM Viktor Prutyanov <viktor@daynix.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, channel I/O and modern PCI
> > > > transports.
> > > >
> > > > Signed-off-by: Viktor Prutyanov <viktor@daynix.com>
> > > > ---
> > > >  v5: replace ternary operator with if-else
> > > >  v4: remove VP_NOTIFY macro and legacy PCI support, add
> > > >     virtio_ccw_kvm_notify_with_data to virtio_ccw
> > > >  v3: support feature in virtio_ccw, remove VM_NOTIFY, use avail_idx_shadow,
> > > >     remove byte swap, rename to vring_notification_data
> > > >  v2: reject the feature in virtio_ccw, replace __le32 with u32
> > > >
> > > >  Tested with disabled VIRTIO_F_NOTIFICATION_DATA on qemu-system-s390x
> > > >  (virtio-blk-ccw), qemu-system-riscv64 (virtio-blk-device,
> > > >  virtio-rng-device), qemu-system-x86_64 (virtio-blk-pci, virtio-net-pci)
> > > >  to make sure nothing is broken.
> > > >  Tested with enabled VIRTIO_F_NOTIFICATION_DATA on 64-bit RISC-V Linux
> > > >  and my hardware implementation of virtio-rng with MMIO.
> > > >
> > > >  drivers/s390/virtio/virtio_ccw.c   | 22 +++++++++++++++++++---
> > > >  drivers/virtio/virtio_mmio.c       | 18 +++++++++++++++++-
> > > >  drivers/virtio/virtio_pci_modern.c | 17 ++++++++++++++++-
> > > >  drivers/virtio/virtio_ring.c       | 17 +++++++++++++++++
> > > >  include/linux/virtio_ring.h        |  2 ++
> > > >  include/uapi/linux/virtio_config.h |  6 ++++++
> > > >  6 files changed, 77 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> > > > index 954fc31b4bc7..9a9c5d34454c 100644
> > > > --- a/drivers/s390/virtio/virtio_ccw.c
> > > > +++ b/drivers/s390/virtio/virtio_ccw.c
> > > > @@ -391,7 +391,7 @@ static void virtio_ccw_drop_indicator(struct virtio_ccw_device *vcdev,
> > > >         ccw_device_dma_free(vcdev->cdev, thinint_area, sizeof(*thinint_area));
> > > >  }
> > > >
> > > > -static bool virtio_ccw_kvm_notify(struct virtqueue *vq)
> > > > +static inline bool virtio_ccw_do_kvm_notify(struct virtqueue *vq, u32 data)
> > > >  {
> > > >         struct virtio_ccw_vq_info *info = vq->priv;
> > > >         struct virtio_ccw_device *vcdev;
> > > > @@ -402,12 +402,22 @@ static bool virtio_ccw_kvm_notify(struct virtqueue *vq)
> > > >         BUILD_BUG_ON(sizeof(struct subchannel_id) != sizeof(unsigned int));
> > > >         info->cookie = kvm_hypercall3(KVM_S390_VIRTIO_CCW_NOTIFY,
> > > >                                       *((unsigned int *)&schid),
> > > > -                                     vq->index, info->cookie);
> > > > +                                     data, info->cookie);
> > > >         if (info->cookie < 0)
> > > >                 return false;
> > > >         return true;
> > > >  }
> > > >
> > > > +static bool virtio_ccw_kvm_notify(struct virtqueue *vq)
> > > > +{
> > > > +       return virtio_ccw_do_kvm_notify(vq, vq->index);
> > > > +}
> > > > +
> > > > +static bool virtio_ccw_kvm_notify_with_data(struct virtqueue *vq)
> > > > +{
> > > > +       return virtio_ccw_do_kvm_notify(vq, vring_notification_data(vq));
> > > > +}
> > > > +
> > > >  static int virtio_ccw_read_vq_conf(struct virtio_ccw_device *vcdev,
> > > >                                    struct ccw1 *ccw, int index)
> > > >  {
> > > > @@ -501,6 +511,12 @@ static struct virtqueue *virtio_ccw_setup_vq(struct virtio_device *vdev,
> > > >         u64 queue;
> > > >         unsigned long flags;
> > > >         bool may_reduce;
> > > > +       bool (*notify)(struct virtqueue *vq);
> > > > +
> > > > +       if (__virtio_test_bit(vdev, VIRTIO_F_NOTIFICATION_DATA))
> > > > +               notify = virtio_ccw_kvm_notify_with_data;
> > > > +       else
> > > > +               notify = virtio_ccw_kvm_notify;
> > > >
> > > >         /* Allocate queue. */
> > > >         info = kzalloc(sizeof(struct virtio_ccw_vq_info), GFP_KERNEL);
> > > > @@ -524,7 +540,7 @@ static struct virtqueue *virtio_ccw_setup_vq(struct virtio_device *vdev,
> > > >         may_reduce = vcdev->revision > 0;
> > > >         vq = vring_create_virtqueue(i, info->num, KVM_VIRTIO_CCW_RING_ALIGN,
> > > >                                     vdev, true, may_reduce, ctx,
> > > > -                                   virtio_ccw_kvm_notify, callback, name);
> > > > +                                   notify, callback, name);
> > > >
> > > >         if (!vq) {
> > > >                 /* For now, we fail if we can't get the requested size. */
> > > > diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> > > > index 3ff746e3f24a..7e87f745f68d 100644
> > > > --- a/drivers/virtio/virtio_mmio.c
> > > > +++ b/drivers/virtio/virtio_mmio.c
> > > > @@ -285,6 +285,16 @@ 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_notification_data(vq);
> > > > +
> > > > +       writel(data, vm_dev->base + VIRTIO_MMIO_QUEUE_NOTIFY);
> > > > +
> > > > +       return true;
> > > > +}
> > > > +
> > > >  /* Notify all virtqueues on an interrupt. */
> > > >  static irqreturn_t vm_interrupt(int irq, void *opaque)
> > > >  {
> > > > @@ -368,6 +378,12 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned int in
> > > >         unsigned long flags;
> > > >         unsigned int num;
> > > >         int err;
> > > > +       bool (*notify)(struct virtqueue *vq);
> > > > +
> > > > +       if (__virtio_test_bit(vdev, VIRTIO_F_NOTIFICATION_DATA))
> > > > +               notify = vm_notify_with_data;
> > > > +       else
> > > > +               notify = vm_notify;
> > > >
> > > >         if (!name)
> > > >                 return NULL;
> > > > @@ -397,7 +413,7 @@ 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, notify, callback, name);
> > > >         if (!vq) {
> > > >                 err = -ENOMEM;
> > > >                 goto error_new_virtqueue;
> > > > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> > > > index 9e496e288cfa..3bfc368b279e 100644
> > > > --- a/drivers/virtio/virtio_pci_modern.c
> > > > +++ b/drivers/virtio/virtio_pci_modern.c
> > > > @@ -288,6 +288,15 @@ static u16 vp_config_vector(struct virtio_pci_device *vp_dev, u16 vector)
> > > >         return vp_modern_config_vector(&vp_dev->mdev, vector);
> > > >  }
> > > >
> > > > +static bool vp_notify_with_data(struct virtqueue *vq)
> > > > +{
> > > > +       u32 data = vring_notification_data(vq);
> > > > +
> > > > +       iowrite32(data, (void __iomem *)vq->priv);
> > > > +
> > > > +       return true;
> > > > +}
> > > > +
> > > >  static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
> > > >                                   struct virtio_pci_vq_info *info,
> > > >                                   unsigned int index,
> > > > @@ -301,6 +310,12 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
> > > >         struct virtqueue *vq;
> > > >         u16 num;
> > > >         int err;
> > > > +       bool (*notify)(struct virtqueue *vq);
> > > > +
> > > > +       if (__virtio_test_bit(&vp_dev->vdev, VIRTIO_F_NOTIFICATION_DATA))
> > > > +               notify = vp_notify_with_data;
> > > > +       else
> > > > +               notify = vp_notify;
> > > >
> > > >         if (index >= vp_modern_get_num_queues(mdev))
> > > >                 return ERR_PTR(-EINVAL);
> > > > @@ -321,7 +336,7 @@ 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);
> > > > +                                   notify, callback, name);
> > > >         if (!vq)
> > > >                 return ERR_PTR(-ENOMEM);
> > > >
> > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > index 4c3bb0ddeb9b..837875cc3190 100644
> > > > --- a/drivers/virtio/virtio_ring.c
> > > > +++ b/drivers/virtio/virtio_ring.c
> > > > @@ -2752,6 +2752,21 @@ void vring_del_virtqueue(struct virtqueue *_vq)
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(vring_del_virtqueue);
> > > >
> > > > +u32 vring_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)) |
> > > > +                       vq->packed.avail_wrap_counter << 15;
> > >
> > > Nit: We have VRING_PACKED_EVENT_F_WRAP_CTR which could be used for
> > > replacing 15 here.
> > >
> > > And we have many places for packing them into u16, it might be better
> > > to introduce a helper.
> >
> > Not sure about a helper, I'd leave that for a future cleanup.
> >
> > However I would use
> >
> > & (-(1 << VRING_PACKED_EVENT_F_WRAP_CTR))
> 
> Do you mean
> & (~(1 << VRING_PACKED_EVENT_F_WRAP_CTR))
> or maybe I missed something?


Sorry.
I meant:

~(-(1 << VRING_PACKED_EVENT_F_WRAP_CTR))

which means "all bits above VRING_PACKED_EVENT_F_WRAP_CTR".


> >
> > that's more robust - works for any value of VRING_PACKED_EVENT_F_WRAP_CTR
> > giving low bits 0 to VRING_PACKED_EVENT_F_WRAP_CTR,
> > and will keep working if someone copypasted it and changed
> > counter to a value different from 15.
> >
> >
> > > Acked-by: Jason Wang <jasowang@redhat.com>
> > >
> > > Thanks
> > >
> > > > +       else
> > > > +               next = vq->split.avail_idx_shadow;
> > > > +
> > > > +       return next << 16 | _vq->index;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(vring_notification_data);
> > > > +
> > > >  /* Manipulates transport-specific feature bits. */
> > > >  void vring_transport_features(struct virtio_device *vdev)
> > > >  {
> > > > @@ -2771,6 +2786,8 @@ 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 8b95b69ef694..2550c9170f4f 100644
> > > > --- a/include/linux/virtio_ring.h
> > > > +++ b/include/linux/virtio_ring.h
> > > > @@ -117,4 +117,6 @@ 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_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
> > > >
> >