Re: [PATCH v7 05/15] s390/vfio-ap: Callback to get/set vfio device mig state during guest migration

["Jason J. Herne" <jjherne@linux.ibm.com>]

On 8/7/26 6:18 PM, Anthony Krowiak wrote:
> Implements two callbacks related to the current state of a vfio-ap device:
> * The callback that sets a new migration state of a vfio-ap device during
>    live migration of guests with pass-through access to AP devices. This
>    callback is mandatory for VFIO_DEVICE_FEATURE_MIGRATION support.
> 
>    The function pointer for this callback is specified via the
>    'migration_set_state' field of the 'vfio_migration_ops' structure
>    which is stored with the VFIO device when the 'vfio_device'
>    structure representing the mediated device is initialized.
> 
> * The callback that returns the current vfio device migration state during
>    live migration of guests with pass-through access to AP devices.
> 
>    The function pointer for this callback is specified via the
>    'migration_get_state' field of the 'vfio_migration_ops' structure
>    which is stored with the VFIO device when the 'vfio_device'
>    structure representing the mediated device is initialized.
> 
> Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
> ---
>   drivers/s390/crypto/vfio_ap_migration.c | 130 +++++++++++++++++++++++-
>   1 file changed, 128 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
> index 1613813124b6..af740b177c97 100644
> --- a/drivers/s390/crypto/vfio_ap_migration.c
> +++ b/drivers/s390/crypto/vfio_ap_migration.c
> @@ -128,16 +128,141 @@ static void vfio_ap_release_resuming_file(struct vfio_ap_migration_data *mig_dat
>   	 */
>   }
>   
> +static struct file *
> +vfio_ap_transition_to_state(struct ap_matrix_mdev *matrix_mdev,
> +			    enum vfio_device_mig_state new_state)
> +{
> +	struct vfio_ap_migration_data *mig_data;
> +	enum vfio_device_mig_state cur_state;
> +
> +	lockdep_assert_held(&matrix_dev->mdevs_lock);
> +	mig_data = matrix_mdev->mig_data;
> +	cur_state = mig_data->mig_state;
> +	dev_dbg(matrix_mdev->vdev.dev, "%s: %d -> %d\n", __func__, cur_state,
> +		new_state);
> +
> +	if (cur_state == VFIO_DEVICE_STATE_STOP &&
> +	    new_state == VFIO_DEVICE_STATE_STOP_COPY) {
> +		/* TODO */
> +		return ERR_PTR(-EOPNOTSUPP);
> +	}
> +
> +	if (cur_state == VFIO_DEVICE_STATE_STOP &&
> +	    new_state == VFIO_DEVICE_STATE_RESUMING) {
> +		/* TODO */
> +		return ERR_PTR(-EOPNOTSUPP);
> +	}
> +
> +	if ((cur_state == VFIO_DEVICE_STATE_RESUMING &&
> +	     new_state == VFIO_DEVICE_STATE_STOP) ||
> +	    (cur_state == VFIO_DEVICE_STATE_STOP_COPY &&
> +	     new_state == VFIO_DEVICE_STATE_STOP)) {
> +		/* TODO */
> +		return ERR_PTR(-EOPNOTSUPP);
> +	}
> +
> +	if ((cur_state == VFIO_DEVICE_STATE_STOP &&
> +	     new_state == VFIO_DEVICE_STATE_RUNNING) ||
> +	    (cur_state == VFIO_DEVICE_STATE_RUNNING &&
> +	     new_state == VFIO_DEVICE_STATE_STOP)) {
> +		/* TODO */
> +		return ERR_PTR(-EOPNOTSUPP);
> +	}
> +
> +	/* vfio_mig_get_next_state() does not use arcs other than the above */
> +	WARN_ON(true);
> +
> +	return ERR_PTR(-EINVAL);
> +}
> +
>   static struct file *vfio_ap_set_state(struct vfio_device *vdev,
>   				      enum vfio_device_mig_state  new_state)
>   {
> -	return NULL;
> +	int ret;
> +	struct file *filp = NULL;
> +	struct ap_matrix_mdev *matrix_mdev;
> +	enum vfio_device_mig_state next_state;
> +	struct vfio_ap_migration_data *mig_data;
> +
> +	matrix_mdev = container_of(vdev, struct ap_matrix_mdev, vdev);

The container_of() pointer swizzle is done under lock in 
vfio_ap_get_state, but not here. Why? They should probably be handled 
consistently.

> +
> +	mutex_lock(&matrix_dev->mdevs_lock);
> +	if (ap_is_se_guest()) {
> +		dev_err_once(matrix_mdev->vdev.dev,
> +			     "Migration not allowed from or to a Secure Execution guest\n");
> +		mutex_unlock(&matrix_dev->mdevs_lock);
> +		return ERR_PTR(-EPERM);
> +	}
> +
> +	mig_data = matrix_mdev->mig_data;
> +
> +	/*
> +	 * The mig_data pointer is set in the vfio_ap_init_migration_data
> +	 * function which is called when the vfio-ap device fd is opened.
> +	 * Since the implicit pre-open state is RUNNING, a request to set
> +	 * RUNNING is a no-op. Any other state transition is invalid before
> +	 * open_device.
> +	 */
> +	if (!mig_data) {
> +		mutex_unlock(&matrix_dev->mdevs_lock);
> +		if (new_state == VFIO_DEVICE_STATE_RUNNING)
> +			return NULL;
> +		return ERR_PTR(-ENODEV);
> +	}
> +
> +	dev_dbg(vdev->dev, "%s -> %d\n", __func__, new_state);
> +
> +	while (mig_data->mig_state != VFIO_DEVICE_STATE_ERROR &&
> +	       mig_data->mig_state != new_state) {
> +		ret = vfio_mig_get_next_state(vdev, mig_data->mig_state,
> +					      new_state, &next_state);
> +		if (ret) {
> +			filp = ERR_PTR(ret);
> +			break;
> +		}
> +
> +		filp = vfio_ap_transition_to_state(matrix_mdev, next_state);
> +		if (IS_ERR(filp))
> +			break;
> +
> +		mig_data->mig_state = next_state;
> +
> +		if (WARN_ON(filp && new_state != next_state)) {
> +			fput(filp);
> +			filp = ERR_PTR(-EINVAL);
> +			break;
> +		}
> +	}
> +
> +	mutex_unlock(&matrix_dev->mdevs_lock);
> +
> +	return filp;
>   }
>   
>   static int vfio_ap_get_state(struct vfio_device *vdev,
>   			     enum vfio_device_mig_state  *current_state)
>   {
> -	return -EOPNOTSUPP;
> +	struct ap_matrix_mdev *matrix_mdev;
> +	struct vfio_ap_migration_data *mig_data;
> +
> +	mutex_lock(&matrix_dev->mdevs_lock);
> +
> +	matrix_mdev = container_of(vdev, struct ap_matrix_mdev, vdev);
> +	mig_data =  matrix_mdev->mig_data;

Why bother with temp variable? You could just access 
matrix_mdev->mig_data directly.

> +
> +	/*
> +	 * The mig_data pointer is set in the vfio_ap_init_migration_data
> +	 * function which is called when the vfio-ap device fd is opened.
> +	 * If mig_data is NULL, report RUNNING as the implicit pre-open state
> +	 * so userspace doesn't need to perform any state transition before the
> +	 * device becomes active.
> +	 */
> +	*current_state = (mig_data) ? mig_data->mig_state :
> +				      VFIO_DEVICE_STATE_RUNNING;
> +
> +	mutex_unlock(&matrix_dev->mdevs_lock);
> +
> +	return 0;
>   }
>   
>   static int vfio_ap_get_data_size(struct vfio_device *vdev,
> @@ -159,6 +284,7 @@ static const struct vfio_migration_ops vfio_ap_migration_ops = {
>    */
>   void vfio_ap_init_migration_capabilities(struct ap_matrix_mdev *matrix_mdev)
>   {
> +	/* Live guest migration is not supported for SE guests */
>   	if (ap_is_se_guest())
>   		return;
>   

Comment is unrelated to the rest of the patch.