vhost-vdpa: Introduce RESUME backend feature bit

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@redhat.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Message-Id: <b18db236ba3d990cdb41278eb4703be9201d9514.1672742878.git.sebastien.boeuf@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

drivers/vhost/vdpa.c

@@ -359,6 +359,14 @@ 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;
@@ -606,11 +614,15 @@ 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;
 		vhost_set_backend_features(&v->vdev, features);
 		return 0;
 	}
@@ -662,6 +674,8 @@ 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;

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