[PATCH v1 22/24] s390/vfio-ap: Provide API to query whether migration is in progress

[Anthony Krowiak]

Provides an AP to query whether a live guest migration is in progress. This
can be called to determine whether an action should be allowed during
migration; for example, allowing a system administrator to disable
migration while it is in progress. Other uses may be to prevent changing
a guest's AP configuration while a migration is in progress.

The only means the vfio_ap device driver has to determine that a migration
is in progress is via the callback functions specified in the
'struct vfio_migration_ops' object associated with the vfio device.
The very first callback invoked during migration is the callback specified
in the 'migration_get_data_size' field of the structure. This callback will
set a flag indicating that migration is in progress. The flag will be
cleared when the vfio device migration state transitions from
VFIO_DEVICE_STATE_STOP_COPY to VFIO_DEVICE_STATE_STOP. At this point, the
internal state of the vfio device on the source has been copied and will
be restored on the target.

Note that the 'migration_get_data_size' callback occurs after migration has
been initiated, so there is a short period of time during which the API
will erroneously indicate migration is not in progress. This,
unfortunately, is unavoidable given the only means of determining that a
migration is in progress is via these callbacks.

Signed-off-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
---
 drivers/s390/crypto/vfio_ap_migration.c | 40 ++++++++++++++++++++++++-
 drivers/s390/crypto/vfio_ap_private.h   |  1 +
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
index fa163b129c66..8a7628fcf285 100644
--- a/drivers/s390/crypto/vfio_ap_migration.c
+++ b/drivers/s390/crypto/vfio_ap_migration.c
@@ -47,11 +47,14 @@
  * @mig_state:		the current migration state
  * @resuming_migf:	the object used to resume the target guest
  * @saving_migf:	the object used to save the state of the source guest
+ * @mig_in_progress	flag indicating whether migration is in progress (true)
+ *			or not (false)
  */
 struct vfio_ap_migration_data {
 	enum vfio_device_mig_state	mig_state;
 	struct vfio_ap_migration_file	*resuming_migf;
 	struct vfio_ap_migration_file	*saving_migf;
+	bool				mig_in_progress;
 };
 
 /**
@@ -971,18 +974,30 @@ vfio_ap_transition_to_state(struct ap_matrix_mdev *matrix_mdev,
 	return ERR_PTR(-EINVAL);
 }
 
+static void vfio_ap_set_mig_in_progress(struct vfio_ap_migration_data *mig_data,
+					enum vfio_device_mig_state prev_state,
+					enum vfio_device_mig_state new_state)
+{
+	lockdep_assert_held(&matrix_dev->mdevs_lock);
+	if (prev_state == VFIO_DEVICE_STATE_STOP_COPY &&
+	    new_state == VFIO_DEVICE_STATE_STOP) {
+		mig_data->mig_in_progress = false;
+	}
+}
+
 static struct file *vfio_ap_set_state(struct vfio_device *vdev,
 				      enum vfio_device_mig_state  new_state)
 {
 	int ret;
 	struct file *filp = NULL;
 	struct ap_matrix_mdev *matrix_mdev;
-	enum vfio_device_mig_state next_state;
+	enum vfio_device_mig_state prev_state, next_state;
 	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;
+	prev_state = mig_data->mig_state;
 	dev_dbg(vdev->dev, "%s -> %d\n", __func__, new_state);
 
 	while (mig_data->mig_state != new_state) {
@@ -1006,6 +1021,7 @@ static struct file *vfio_ap_set_state(struct vfio_device *vdev,
 		}
 	}
 
+	vfio_ap_set_mig_in_progress(mig_data, prev_state, new_state);
 	mutex_unlock(&matrix_dev->mdevs_lock);
 
 	return filp;
@@ -1031,12 +1047,15 @@ static int vfio_ap_get_state(struct vfio_device *vdev,
 static int vfio_ap_get_data_size(struct vfio_device *vdev,
 				 unsigned long *stop_copy_length)
 {
+	struct vfio_ap_migration_data *mig_data;
 	struct ap_matrix_mdev *matrix_mdev;
 	size_t qinfo_sz;
 	int num_queues;
 
 	mutex_lock(&matrix_dev->mdevs_lock);
 	matrix_mdev = container_of(vdev, struct ap_matrix_mdev, vdev);
+	mig_data = matrix_mdev->mig_data;
+	mig_data->mig_in_progress = true;
 	num_queues = vfio_ap_mdev_get_num_queues(&matrix_mdev->shadow_apcb);
 	qinfo_sz = num_queues * sizeof(struct vfio_ap_queue_info);
 	*stop_copy_length = qinfo_sz + sizeof(struct vfio_ap_config);
@@ -1051,6 +1070,24 @@ static const struct vfio_migration_ops vfio_ap_migration_ops = {
 	.migration_get_data_size = vfio_ap_get_data_size,
 };
 
+/**
+ * vfio_ap_migration_in_progress: Indicates whether a live guest migration is in
+ *				  progress or not.
+ *
+ * @matrix_mdev: pointer to object maintaining the vfio device state
+ *
+ * Return: returns true if a migration is in progress; otherwise, returns false.
+ */
+bool vfio_ap_migration_in_progress(struct ap_matrix_mdev *matrix_mdev)
+{
+	struct vfio_ap_migration_data *mig_data;
+
+	lockdep_assert_held(&matrix_dev->mdevs_lock);
+	mig_data = matrix_mdev->mig_data;
+
+	return mig_data->mig_in_progress;
+}
+
 /**
  * vfio_ap_init_migration_data - initialize migration data and functions
  *
@@ -1069,6 +1106,7 @@ int vfio_ap_init_migration_data(struct ap_matrix_mdev *matrix_mdev)
 		return -ENOMEM;
 
 	mig_data->mig_state = VFIO_DEVICE_STATE_STOP;
+	mig_data->mig_in_progress = false;
 	matrix_mdev->vdev.migration_flags = VFIO_MIGRATION_STOP_COPY;
 	matrix_mdev->vdev.mig_ops = &vfio_ap_migration_ops;
 	matrix_mdev->mig_data = mig_data;
diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
index cad49b509f7a..e04644c335fe 100644
--- a/drivers/s390/crypto/vfio_ap_private.h
+++ b/drivers/s390/crypto/vfio_ap_private.h
@@ -183,5 +183,6 @@ void vfio_ap_on_scan_complete(struct ap_config_info *new_config_info,
 
 int vfio_ap_init_migration_data(struct ap_matrix_mdev *matrix_mdev);
 void vfio_ap_release_migration_data(struct ap_matrix_mdev *matrix_mdev);
+bool vfio_ap_migration_in_progress(struct ap_matrix_mdev *matrix_mdev);
 
 #endif /* _VFIO_AP_PRIVATE_H_ */
-- 
2.52.0