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

Michael S. Tsirkin
2023-03-21T09:28:30Z

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