netdev - Re: [PATCH V2 3/4] vp_vdpa: allow set vq state to initial state after reset

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Date:   Wed, 2 Jun 2021 09:13:24 +0300
From:   Eli Cohen <elic@...dia.com>
To:     Jason Wang <jasowang@...hat.com>
CC:     <mst@...hat.com>, <virtualization@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <netdev@...r.kernel.org>, <eli@...lanox.com>
Subject: Re: [PATCH V2 3/4] vp_vdpa: allow set vq state to initial state
 after reset

On Wed, Jun 02, 2021 at 10:10:42AM +0800, Jason Wang wrote:
> We used to fail the set_vq_state() since it was not supported yet by
> the virtio spec. But if the bus tries to set the state which is equal
> to the device initial state after reset, we can let it go.
> 
> This is a must for virtio_vdpa() to set vq state during probe which is
> required for some vDPA parents.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/vdpa/virtio_pci/vp_vdpa.c | 42 ++++++++++++++++++++++++++++---
>  1 file changed, 39 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
> index c76ebb531212..18bf4a422772 100644
> --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
> +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
> @@ -210,13 +210,49 @@ static int vp_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 qid,
>  	return -EOPNOTSUPP;
>  }
>  
> +static int vp_vdpa_set_vq_state_split(struct vdpa_device *vdpa,
> +				      const struct vdpa_vq_state *state)
> +{
> +	const struct vdpa_vq_state_split *split = &state->split;
> +
> +	if (split->avail_index == 0)
> +		return 0;
> +
> +	return -EOPNOTSUPP;
> +}
> +
> +static int vp_vdpa_set_vq_state_packed(struct vdpa_device *vdpa,
> +				       const struct vdpa_vq_state *state)
> +{
> +	const struct vdpa_vq_state_packed *packed = &state->packed;
> +
> +	if (packed->last_avail_counter == 1 &&
Can you elaborate on the requirement on last_avail_counter and
last_used_counter?

> +	    packed->last_avail_idx == 0 &&
> +	    packed->last_used_counter == 1 &&
> +	    packed->last_used_idx == 0)
> +		return 0;
> +
> +	return -EOPNOTSUPP;
> +}
> +
>  static int vp_vdpa_set_vq_state(struct vdpa_device *vdpa, u16 qid,
>  				const struct vdpa_vq_state *state)
>  {
> -	/* Note that this is not supported by virtio specification, so
> -	 * we return -ENOPOTSUPP here. This means we can't support live
> -	 * migration, vhost device start/stop.
> +	struct virtio_pci_modern_device *mdev = vdpa_to_mdev(vdpa);
> +
> +	/* Note that this is not supported by virtio specification.
> +	 * But if the state is by chance equal to the device initial
> +	 * state, we can let it go.
>  	 */
> +	if ((vp_modern_get_status(mdev) & VIRTIO_CONFIG_S_FEATURES_OK) &&
> +	    !vp_modern_get_queue_enable(mdev, qid)) {
> +		if (vp_modern_get_driver_features(mdev) &
> +		    BIT_ULL(VIRTIO_F_RING_PACKED))
> +			return vp_vdpa_set_vq_state_packed(vdpa, state);
> +		else
> +			return vp_vdpa_set_vq_state_split(vdpa,	state);
> +	}
> +
>  	return -EOPNOTSUPP;
>  }
>  
> -- 
> 2.25.1
>