vhost-vdpa: uAPI to resume the device

This new ioctl adds support for resuming the device from userspace.

This is required when trying to restore the device in a functioning
state after it's been suspended. It is already possible to reset a
suspended device, but that means the device must be reconfigured and
all the IOMMU/IOTLB mappings must be recreated. This new operation
allows the device to be resumed without going through a full reset.

This is particularly useful when trying to perform offline migration of
a virtual machine (also known as snapshot/restore) as it allows the VMM
to resume the virtual machine back to a running state after the snapshot
is performed.
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Message-Id: <73b75fb87d25cff59768b4955a81fe7ffe5b4770.1672742878.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

@@ -506,6 +506,21 @@ static long vhost_vdpa_suspend(struct vhost_vdpa *v)
 	return ops->suspend(vdpa);
 }
 
+/* After a successful return of this ioctl the device resumes processing
+ * virtqueue descriptors. The device becomes fully operational the same way it
+ * was before it was suspended.
+ */
+static long vhost_vdpa_resume(struct vhost_vdpa *v)
+{
+	struct vdpa_device *vdpa = v->vdpa;
+	const struct vdpa_config_ops *ops = vdpa->config;
+
+	if (!ops->resume)
+		return -EOPNOTSUPP;
+
+	return ops->resume(vdpa);
+}
+
 static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 				   void __user *argp)
 {
@@ -691,6 +706,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 	case VHOST_VDPA_SUSPEND:
 		r = vhost_vdpa_suspend(v);
 		break;
+	case VHOST_VDPA_RESUME:
+		r = vhost_vdpa_resume(v);
+		break;
 	default:
 		r = vhost_dev_ioctl(&v->vdev, cmd, argp);
 		if (r == -ENOIOCTLCMD)

include/uapi/linux/vhost.h

@@ -180,4 +180,12 @@
  */
 #define VHOST_VDPA_SUSPEND		_IO(VHOST_VIRTIO, 0x7D)
 
+/* Resume a device so it can resume processing virtqueue requests
+ *
+ * After the return of this ioctl the device will have restored all the
+ * necessary states and it is fully operational to continue processing the
+ * virtqueue descriptors.
+ */
+#define VHOST_VDPA_RESUME		_IO(VHOST_VIRTIO, 0x7E)
+
 #endif