Re: [PATCH v6 2/4] vhost-vdpa: Introduce RESUME backend feature bit

[Stefano Garzarella]

On Tue, Jan 03, 2023 at 11:51:06AM +0100, sebastien.boeuf@xxxxxxxxx wrote:
> From: Sebastien Boeuf <sebastien.boeuf@xxxxxxxxx>
>
> Userspace knows if the device can be resumed or not by checking this
> feature bit.
>
> It's only exposed if the vdpa driver backend implements the resume()
> operation callback. Userspace trying to negotiate this feature when it
> hasn't been exposed will result in an error.
>
> Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> Signed-off-by: Sebastien Boeuf <sebastien.boeuf@xxxxxxxxx>
> ---
> drivers/vhost/vdpa.c             | 16 +++++++++++++++-
> include/uapi/linux/vhost_types.h |  2 ++
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 166044642fd5..833617d00ef6 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -355,6 +355,14 @@ static bool vhost_vdpa_can_suspend(const struct vhost_vdpa *v)
> 	return ops->suspend;
> }
>
> +static bool vhost_vdpa_can_resume(const struct vhost_vdpa *v)
> +{
> +	struct vdpa_device *vdpa = v->vdpa;
> +	const struct vdpa_config_ops *ops = vdpa->config;
> +
> +	return ops->resume;
> +}
> +
> static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
> {
> 	struct vdpa_device *vdpa = v->vdpa;
> @@ -602,11 +610,15 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> 		if (copy_from_user(&features, featurep, sizeof(features)))
> 			return -EFAULT;
> 		if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
> -				 BIT_ULL(VHOST_BACKEND_F_SUSPEND)))
> +				 BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
> +				 BIT_ULL(VHOST_BACKEND_F_RESUME)))
> 			return -EOPNOTSUPP;
> 		if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
> 		     !vhost_vdpa_can_suspend(v))
> 			return -EOPNOTSUPP;
> +		if ((features & BIT_ULL(VHOST_BACKEND_F_RESUME)) &&
> +		     !vhost_vdpa_can_resume(v))
> +			return -EOPNOTSUPP;

Not for this patch, but I'd like to refactor this code a bit to fill a 
`backend_features` field in vhost_vdpa during the vhost_vdpa_probe(), so 
we don't need to change this code or the VHOST_GET_BACKEND_FEATURES for 
every new backend feature.

I'll send a patch.

This LGTM:

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>


> 		vhost_set_backend_features(&v->vdev, features);
> 		return 0;
> 	}
> @@ -658,6 +670,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> 		features = VHOST_VDPA_BACKEND_FEATURES;
> 		if (vhost_vdpa_can_suspend(v))
> 			features |= BIT_ULL(VHOST_BACKEND_F_SUSPEND);
> +		if (vhost_vdpa_can_resume(v))
> +			features |= BIT_ULL(VHOST_BACKEND_F_RESUME);
> 		if (copy_to_user(featurep, &features, sizeof(features)))
> 			r = -EFAULT;
> 		break;
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index 53601ce2c20a..c5690a8992d8 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -163,5 +163,7 @@ struct vhost_vdpa_iova_range {
> #define VHOST_BACKEND_F_IOTLB_ASID  0x3
> /* Device can be suspended */
> #define VHOST_BACKEND_F_SUSPEND  0x4
> +/* Device can be resumed */
> +#define VHOST_BACKEND_F_RESUME  0x5
>
> #endif
> --
> 2.37.2
>
> ---------------------------------------------------------------------
> Intel Corporation SAS (French simplified joint stock company)
> Registered headquarters: "Les Montalets"- 2, rue de Paris,
> 92196 Meudon Cedex, France
> Registration Number:  302 456 199 R.C.S. NANTERRE
> Capital: 5 208 026.16 Euros
>
> This e-mail and any attachments may contain confidential material for
> the sole use of the intended recipient(s). Any review or distribution
> by others is strictly prohibited. If you are not the intended
> recipient, please contact the sender and delete all copies.