Commit b84eb8e0 authored by Tony Krowiak's avatar Tony Krowiak Committed by Alexander Gordeev
Browse files

s390/vfio-ap: use proper locking order when setting/clearing KVM pointer 



The group notifier that handles the VFIO_GROUP_NOTIFY_SET_KVM event must
use the required locks in proper locking order to dynamically update the
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 KVM guest's APCB.

       3. matrix_dev->mdevs_lock: required to store or access the data
          stored in a struct ap_matrix_mdev instance.

Two macros are introduced to acquire and release the locks in the proper
order. These macros are now used by the group notifier functions.

Signed-off-by: default avatarTony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: default avatarJason J. Herne <jjherne@linux.ibm.com>
Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
parent 21195eb0

drivers/s390/crypto/vfio_ap_ops.c

+48 −10
Original line number Diff line number Diff line
@@ -34,6 +34,49 @@ static int vfio_ap_mdev_reset_queues(struct ap_matrix_mdev *matrix_mdev); 
static struct vfio_ap_queue *vfio_ap_find_queue(int apqn);

static const struct vfio_device_ops vfio_ap_matrix_dev_ops;



/**

 * get_update_locks_for_kvm: Acquire the locks required to dynamically update a

 *			     KVM guest's APCB in the proper order.

 *

 * @kvm: a pointer to a struct kvm object containing the 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. 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 @kvm is NULL, the KVM lock will not be taken.

 */

static inline void get_update_locks_for_kvm(struct kvm *kvm)

{

	mutex_lock(&matrix_dev->guests_lock);

	if (kvm)

		mutex_lock(&kvm->lock);

	mutex_lock(&matrix_dev->mdevs_lock);

}



/**

 * release_update_locks_for_kvm: Release the locks used to dynamically update a

 *				 KVM guest's APCB in the proper order.

 *

 * @kvm: a pointer to a struct kvm object containing the KVM guest's APCB.

 *

 * The proper unlocking order is:

 * 1. matrix_dev->mdevs_lock

 * 2. kvm->lock

 * 3. matrix_dev->guests_lock

 *

 * Note: If @kvm is NULL, the KVM lock will not be released.

 */

static inline void release_update_locks_for_kvm(struct kvm *kvm)

{

	mutex_unlock(&matrix_dev->mdevs_lock);

	if (kvm)

		mutex_unlock(&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
@@ -1266,13 +1309,11 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, 
		kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;

		up_write(&kvm->arch.crypto.pqap_hook_rwsem);



		mutex_lock(&kvm->lock);

		mutex_lock(&matrix_dev->mdevs_lock);

		get_update_locks_for_kvm(kvm);



		list_for_each_entry(m, &matrix_dev->mdev_list, node) {

			if (m != matrix_mdev && m->kvm == kvm) {

				mutex_unlock(&kvm->lock);

				mutex_unlock(&matrix_dev->mdevs_lock);

				release_update_locks_for_kvm(kvm);

				return -EPERM;

			}

		}
@@ -1283,8 +1324,7 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, 
					  matrix_mdev->shadow_apcb.aqm,

					  matrix_mdev->shadow_apcb.adm);



		mutex_unlock(&kvm->lock);

		mutex_unlock(&matrix_dev->mdevs_lock);

		release_update_locks_for_kvm(kvm);

	}



	return 0;
@@ -1335,16 +1375,14 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) 
		kvm->arch.crypto.pqap_hook = NULL;

		up_write(&kvm->arch.crypto.pqap_hook_rwsem);



		mutex_lock(&kvm->lock);

		mutex_lock(&matrix_dev->mdevs_lock);

		get_update_locks_for_kvm(kvm);



		kvm_arch_crypto_clear_masks(kvm);

		vfio_ap_mdev_reset_queues(matrix_mdev);

		kvm_put_kvm(kvm);

		matrix_mdev->kvm = NULL;



		mutex_unlock(&kvm->lock);

		mutex_unlock(&matrix_dev->mdevs_lock);

		release_update_locks_for_kvm(kvm);

	}

}