s390/vfio-ap: r/w lock for PQAP interception handler function pointer

The function pointer to the interception handler for the PQAP instruction
can get changed during the interception process. Let's add a
semaphore to struct kvm_s390_crypto to control read/write access to the
function pointer contained therein.

The semaphore must be locked for write access by the vfio_ap device driver
when notified that the KVM pointer has been set or cleared. It must be
locked for read access by the interception framework when the PQAP
instruction is intercepted.

Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lore.kernel.org/r/20210823212047.1476436-2-akrowiak@linux.ibm.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

2 files changed, 18 insertions, 7 deletions

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index cee5626fe0a4..439ca7768eb7 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -352,8 +352,7 @@ static int vfio_ap_mdev_create(struct mdev_device *mdev)
 	vfio_ap_matrix_init(&matrix_dev->info, &matrix_mdev->matrix);
 	init_waitqueue_head(&matrix_mdev->wait_for_kvm);
 	mdev_set_drvdata(mdev, matrix_mdev);
-	matrix_mdev->pqap_hook.hook = handle_pqap;
-	matrix_mdev->pqap_hook.owner = THIS_MODULE;
+	matrix_mdev->pqap_hook = handle_pqap;
 	mutex_lock(&matrix_dev->lock);
 	list_add(&matrix_mdev->node, &matrix_dev->mdev_list);
 	mutex_unlock(&matrix_dev->lock);
@@ -1115,15 +1114,20 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
 		}
 
 		kvm_get_kvm(kvm);
+		matrix_mdev->kvm = kvm;
 		matrix_mdev->kvm_busy = true;
 		mutex_unlock(&matrix_dev->lock);
+
+		down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
+		kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
+		up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
+
 		kvm_arch_crypto_set_masks(kvm,
 					  matrix_mdev->matrix.apm,
 					  matrix_mdev->matrix.aqm,
 					  matrix_mdev->matrix.adm);
+
 		mutex_lock(&matrix_dev->lock);
-		kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
-		matrix_mdev->kvm = kvm;
 		matrix_mdev->kvm_busy = false;
 		wake_up_all(&matrix_mdev->wait_for_kvm);
 	}
@@ -1189,10 +1193,17 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
 	if (matrix_mdev->kvm) {
 		matrix_mdev->kvm_busy = true;
 		mutex_unlock(&matrix_dev->lock);
-		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
+
+		if (matrix_mdev->kvm->arch.crypto.crycbd) {
+			down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
+			matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
+			up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
+
+			kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
+		}
+
 		mutex_lock(&matrix_dev->lock);
 		vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
-		matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
 		kvm_put_kvm(matrix_mdev->kvm);
 		matrix_mdev->kvm = NULL;
 		matrix_mdev->kvm_busy = false;
diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
index f82a6396acae..e12218e5a629 100644
--- a/drivers/s390/crypto/vfio_ap_private.h
+++ b/drivers/s390/crypto/vfio_ap_private.h
@@ -86,7 +86,7 @@ struct ap_matrix_mdev {
 	bool kvm_busy;
 	wait_queue_head_t wait_for_kvm;
 	struct kvm *kvm;
-	struct kvm_s390_module_hook pqap_hook;
+	crypto_hook pqap_hook;
 	struct mdev_device *mdev;
 };