s390/vfio-ap: prepare for dynamic update of guest's APCB on assign/unassign

The functions backing the matrix mdev's sysfs attribute interfaces to
assign/unassign adapters, domains and control domains must take and
release the locks required to perform a dynamic update of a guest's APCB
in the proper order.

The proper order for taking the locks is:

matrix_dev->guests_lock => kvm->lock => matrix_dev->mdevs_lock

The proper order for releasing the locks is:

matrix_dev->mdevs_lock => kvm->lock => matrix_dev->guests_lock

Two new macros are introduced for this purpose: One to take the locks and
the other to release the locks. These macros will be used by the
assignment/unassignment functions to prepare for dynamic update of
the KVM guest's APCB.
Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

drivers/s390/crypto/vfio_ap_ops.c

@@ -77,6 +77,53 @@ static inline void release_update_locks_for_kvm(struct kvm *kvm)
 	mutex_unlock(&matrix_dev->guests_lock);
 }
 
+/**
+ * get_update_locks_for_mdev: Acquire the locks required to dynamically update a
+ *			      KVM guest's APCB in the proper order.
+ *
+ * @matrix_mdev: a pointer to a struct ap_matrix_mdev object containing the AP
+ *		 configuration data to use to update a KVM guest's APCB.
+ *
+ * The proper locking order is:
+ * 1. matrix_dev->guests_lock: required to use the KVM pointer to update a KVM
+ *			       guest's APCB.
+ * 2. matrix_mdev->kvm->lock:  required to update a guest's APCB
+ * 3. matrix_dev->mdevs_lock:  required to access data stored in a matrix_mdev
+ *
+ * Note: If @matrix_mdev is NULL or is not attached to a KVM guest, the KVM
+ *	 lock will not be taken.
+ */
+static inline void get_update_locks_for_mdev(struct ap_matrix_mdev *matrix_mdev)
+{
+	mutex_lock(&matrix_dev->guests_lock);
+	if (matrix_mdev && matrix_mdev->kvm)
+		mutex_lock(&matrix_mdev->kvm->lock);
+	mutex_lock(&matrix_dev->mdevs_lock);
+}
+
+/**
+ * release_update_locks_for_mdev: Release the locks used to dynamically update a
+ *				  KVM guest's APCB in the proper order.
+ *
+ * @matrix_mdev: a pointer to a struct ap_matrix_mdev object containing the AP
+ *		 configuration data to use to update a KVM guest's APCB.
+ *
+ * The proper unlocking order is:
+ * 1. matrix_dev->mdevs_lock
+ * 2. matrix_mdev->kvm->lock
+ * 3. matrix_dev->guests_lock
+ *
+ * Note: If @matrix_mdev is NULL or is not attached to a KVM guest, the KVM
+ *	 lock will not be released.
+ */
+static inline void release_update_locks_for_mdev(struct ap_matrix_mdev *matrix_mdev)
+{
+	mutex_unlock(&matrix_dev->mdevs_lock);
+	if (matrix_mdev && matrix_mdev->kvm)
+		mutex_unlock(&matrix_mdev->kvm->lock);
+	mutex_unlock(&matrix_dev->guests_lock);
+}
+
 /**
  * vfio_ap_mdev_get_queue - retrieve a queue with a specific APQN from a
  *			    hash table of queues assigned to a matrix mdev
@@ -832,7 +879,7 @@ static ssize_t assign_adapter_store(struct device *dev,
 
 	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
 
-	mutex_lock(&matrix_dev->mdevs_lock);
+	get_update_locks_for_mdev(matrix_mdev);
 
 	/* If the KVM guest is running, disallow assignment of adapter */
 	if (matrix_mdev->kvm) {
@@ -864,7 +911,7 @@ static ssize_t assign_adapter_store(struct device *dev,
 				   matrix_mdev->matrix.aqm, matrix_mdev);
 	ret = count;
 done:
-	mutex_unlock(&matrix_dev->mdevs_lock);
+	release_update_locks_for_mdev(matrix_mdev);
 
 	return ret;
 }
@@ -907,7 +954,7 @@ static ssize_t unassign_adapter_store(struct device *dev,
 	unsigned long apid;
 	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
 
-	mutex_lock(&matrix_dev->mdevs_lock);
+	get_update_locks_for_mdev(matrix_mdev);
 
 	/* If the KVM guest is running, disallow unassignment of adapter */
 	if (matrix_mdev->kvm) {
@@ -932,7 +979,7 @@ static ssize_t unassign_adapter_store(struct device *dev,
 
 	ret = count;
 done:
-	mutex_unlock(&matrix_dev->mdevs_lock);
+	release_update_locks_for_mdev(matrix_mdev);
 	return ret;
 }
 static DEVICE_ATTR_WO(unassign_adapter);
@@ -987,7 +1034,7 @@ static ssize_t assign_domain_store(struct device *dev,
 	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
 	unsigned long max_apqi = matrix_mdev->matrix.aqm_max;
 
-	mutex_lock(&matrix_dev->mdevs_lock);
+	get_update_locks_for_mdev(matrix_mdev);
 
 	/* If the KVM guest is running, disallow assignment of domain */
 	if (matrix_mdev->kvm) {
@@ -1018,7 +1065,7 @@ static ssize_t assign_domain_store(struct device *dev,
 				   matrix_mdev);
 	ret = count;
 done:
-	mutex_unlock(&matrix_dev->mdevs_lock);
+	release_update_locks_for_mdev(matrix_mdev);
 
 	return ret;
 }
@@ -1061,7 +1108,7 @@ static ssize_t unassign_domain_store(struct device *dev,
 	unsigned long apqi;
 	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
 
-	mutex_lock(&matrix_dev->mdevs_lock);
+	get_update_locks_for_mdev(matrix_mdev);
 
 	/* If the KVM guest is running, disallow unassignment of domain */
 	if (matrix_mdev->kvm) {
@@ -1087,7 +1134,7 @@ static ssize_t unassign_domain_store(struct device *dev,
 	ret = count;
 
 done:
-	mutex_unlock(&matrix_dev->mdevs_lock);
+	release_update_locks_for_mdev(matrix_mdev);
 	return ret;
 }
 static DEVICE_ATTR_WO(unassign_domain);
@@ -1114,7 +1161,7 @@ static ssize_t assign_control_domain_store(struct device *dev,
 	unsigned long id;
 	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
 
-	mutex_lock(&matrix_dev->mdevs_lock);
+	get_update_locks_for_mdev(matrix_mdev);
 
 	/* If the KVM guest is running, disallow assignment of control domain */
 	if (matrix_mdev->kvm) {
@@ -1140,7 +1187,7 @@ static ssize_t assign_control_domain_store(struct device *dev,
 	vfio_ap_mdev_filter_cdoms(matrix_mdev);
 	ret = count;
 done:
-	mutex_unlock(&matrix_dev->mdevs_lock);
+	release_update_locks_for_mdev(matrix_mdev);
 	return ret;
 }
 static DEVICE_ATTR_WO(assign_control_domain);
@@ -1168,7 +1215,7 @@ static ssize_t unassign_control_domain_store(struct device *dev,
 	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
 	unsigned long max_domid =  matrix_mdev->matrix.adm_max;
 
-	mutex_lock(&matrix_dev->mdevs_lock);
+	get_update_locks_for_mdev(matrix_mdev);
 
 	/* If a KVM guest is running, disallow unassignment of control domain */
 	if (matrix_mdev->kvm) {
@@ -1191,7 +1238,7 @@ static ssize_t unassign_control_domain_store(struct device *dev,
 
 	ret = count;
 done:
-	mutex_unlock(&matrix_dev->mdevs_lock);
+	release_update_locks_for_mdev(matrix_mdev);
 	return ret;
 }
 static DEVICE_ATTR_WO(unassign_control_domain);