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

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

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);
>  	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)

btw what does "fill" mean here? why not just vring_notification_data?

> +{
> +	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);
> +	else
> +		next = virtio16_to_cpu(_vq->vdev, vq->split.vring.avail->idx);

BTW it's annoying to poke at avail->idx here - will cause a bunch of
cache misses. And the byte-swap is a waste.

Isn't this why we have avail_idx_shadow?

> +
> +	return ((u32)next << 16) | _vq->index;
> +}
> +EXPORT_SYMBOL_GPL(vring_fill_notification_data);
> +
>  /* 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