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From:   Tony Krowiak <akrowiak@linux.ibm.com>
To:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     jjherne@linux.ibm.com, freude@linux.ibm.com,
        borntraeger@de.ibm.com, cohuck@redhat.com, mjrosato@linux.ibm.com,
        pasic@linux.ibm.com, alex.williamson@redhat.com,
        kwankhede@nvidia.com, fiuczy@linux.ibm.com
Subject: [PATCH v20 10/20] s390/vfio-ap: prepare for dynamic update of guest's APCB on assign/unassign
Date:   Tue, 21 Jun 2022 11:51:24 -0400
Message-Id: <20220621155134.1932383-11-akrowiak@linux.ibm.com>
In-Reply-To: <20220621155134.1932383-1-akrowiak@linux.ibm.com>
References: <20220621155134.1932383-1-akrowiak@linux.ibm.com>
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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>
---
 drivers/s390/crypto/vfio_ap_ops.c | 69 +++++++++++++++++++++++++------
 1 file changed, 57 insertions(+), 12 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index f31db1248740..b8f901e6b580 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -75,6 +75,51 @@ static const struct vfio_device_ops vfio_ap_matrix_dev_ops;
 	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.
+ */
+#define get_update_locks_for_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.
+ */
+#define release_update_locks_for_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
@@ -830,7 +875,7 @@ 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) {
@@ -862,7 +907,7 @@ 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;
 }
@@ -905,7 +950,7 @@ 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) {
@@ -930,7 +975,7 @@ 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);
@@ -985,7 +1030,7 @@ 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) {
@@ -1016,7 +1061,7 @@ 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;
 }
@@ -1059,7 +1104,7 @@ 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) {
@@ -1085,7 +1130,7 @@ 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);
@@ -1112,7 +1157,7 @@ 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) {
@@ -1138,7 +1183,7 @@ 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);
@@ -1166,7 +1211,7 @@ 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) {
@@ -1189,7 +1234,7 @@ 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);
-- 
2.35.3