From:   Cornelia Huck <cohuck@redhat.com>
To:     Viktor Prutyanov <viktor@daynix.com>, mst@redhat.com,
        jasowang@redhat.com
Cc:     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, viktor@daynix.com
Subject: Re: [PATCH v3] virtio: add VIRTIO_F_NOTIFICATION_DATA feature support
In-Reply-To: <20230321134410.2097163-1-viktor@daynix.com>
Organization: Red Hat GmbH
References: <20230321134410.2097163-1-viktor@daynix.com>
User-Agent: Notmuch/0.37 (https://notmuchmail.org)
Date:   Tue, 21 Mar 2023 15:59:07 +0100
Message-ID: <87h6uem9qc.fsf@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Tue, Mar 21 2023, 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, PCI and channel I/O transports.
>
> Signed-off-by: Viktor Prutyanov <viktor@daynix.com>
> ---
>  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
>
>  drivers/s390/virtio/virtio_ccw.c   |  4 +++-
>  drivers/virtio/virtio_mmio.c       | 14 +++++++++++++-
>  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, 57 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> index 954fc31b4bc7..c33172c5b8d5 100644
> --- a/drivers/s390/virtio/virtio_ccw.c
> +++ b/drivers/s390/virtio/virtio_ccw.c
> @@ -396,13 +396,15 @@ static bool virtio_ccw_kvm_notify(struct virtqueue *vq)
>  	struct virtio_ccw_vq_info *info = vq->priv;
>  	struct virtio_ccw_device *vcdev;
>  	struct subchannel_id schid;
> +	u32 data = __virtio_test_bit(vq->vdev, VIRTIO_F_NOTIFICATION_DATA) ?
> +			vring_notification_data(vq) : vq->index;
>  
>  	vcdev = to_vc_device(info->vq->vdev);
>  	ccw_device_get_schid(vcdev->cdev, &schid);
>  	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;
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index 3ff746e3f24a..7c16e622c33d 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);

Can't you simply use the same method as for ccw, i.e. use one callback
function that simply writes one value or the other?

> +
> +	return true;
> +}
> +
>  /* Notify all virtqueues on an interrupt. */
>  static irqreturn_t vm_interrupt(int irq, void *opaque)
>  {
> @@ -368,6 +378,8 @@ 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) = __virtio_test_bit(vdev,
> +		VIRTIO_F_NOTIFICATION_DATA) ? vm_notify_with_data : vm_notify;
>  
>  	if (!name)
>  		return NULL;
> @@ -397,7 +409,7 @@ 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_common.c b/drivers/virtio/virtio_pci_common.c
> index a6c86f916dbd..e915c22f2384 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_notification_data(vq);
> +
> +	iowrite32(data, (void __iomem *)vq->priv);

Same for pci.

> +
>  	return true;
>  }
>