[PATCH v6 3/7] s390: ap: setup relation betwen KVM and mediated device

[Pierre Morel <pmorel@linux.ibm.com>]

When the mediated device is open we setup the relation with KVM unset it
when the mediated device is released.

We lock the matrix mediated device to avoid any change until the
open is done.
We make sure that KVM is present when opening the mediated device
otherwise we return an error.

Increase kvm's refcount to ensure the KVM structures are still available
during the use of the mediated device by the guest.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 143 +++++++++++++++++++++-----------------
 1 file changed, 79 insertions(+), 64 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 77f7bac..bdb36e0 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -787,74 +787,24 @@ static const struct attribute_group *vfio_ap_mdev_attr_groups[] = {
 	NULL
 };
 
-/**
- * vfio_ap_mdev_set_kvm
- *
- * @matrix_mdev: a mediated matrix device
- * @kvm: reference to KVM instance
- *
- * Verifies no other mediated matrix device has @kvm and sets a reference to
- * it in @matrix_mdev->kvm.
- *
- * Return 0 if no other mediated matrix device has a reference to @kvm;
- * otherwise, returns an -EPERM.
- */
-static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
-				struct kvm *kvm)
-{
-	struct ap_matrix_mdev *m;
-
-	mutex_lock(&matrix_dev->lock);
-
-	list_for_each_entry(m, &matrix_dev->mdev_list, node) {
-		if ((m != matrix_mdev) && (m->kvm == kvm)) {
-			mutex_unlock(&matrix_dev->lock);
-			return -EPERM;
-		}
-	}
-
-	matrix_mdev->kvm = kvm;
-	mutex_unlock(&matrix_dev->lock);
-
-	return 0;
-}
-
 static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
 				       unsigned long action, void *data)
 {
-	int ret;
 	struct ap_matrix_mdev *matrix_mdev;
 
 	if (action != VFIO_GROUP_NOTIFY_SET_KVM)
 		return NOTIFY_OK;
 
 	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
-
-	if (!data) {
-		matrix_mdev->kvm = NULL;
-		return NOTIFY_OK;
-	}
-
-	ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
-	if (ret)
-		return NOTIFY_DONE;
-
-	/* If there is no CRYCB pointer, then we can't copy the masks */
-	if (!matrix_mdev->kvm->arch.crypto.crycbd)
-		return NOTIFY_DONE;
-
-	kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
-				  matrix_mdev->matrix.aqm,
-				  matrix_mdev->matrix.adm);
+	matrix_mdev->kvm = data;
 
 	return NOTIFY_OK;
 }
 
-static int vfio_ap_mdev_reset_queues(struct mdev_device *mdev)
+static int vfio_ap_mdev_reset_queues(struct ap_matrix_mdev *matrix_mdev)
 {
 	int ret;
 	int rc = 0;
-	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 	struct vfio_ap_queue *q;
 
 	list_for_each_entry(q, &matrix_mdev->qlist, list) {
@@ -871,41 +821,106 @@ static int vfio_ap_mdev_reset_queues(struct mdev_device *mdev)
 	return rc;
 }
 
+/**
+ * vfio_ap_mdev_set_kvm
+ *
+ * @matrix_mdev: a mediated matrix device
+ *
+ * - Verifies that the hook is free and install the PQAP hook
+ * - Copy the matrix masks inside the CRYCB
+ * - Increment the KVM rerference count
+ *
+ * Return 0 if no other mediated matrix device has a reference to @kvm;
+ * otherwise, returns an -EPERM.
+ */
+static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev)
+{
+	if (matrix_mdev->kvm->arch.crypto.pqap_hook)
+		return -EPERM;
+	matrix_mdev->kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
+
+	kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
+				  matrix_mdev->matrix.aqm,
+				  matrix_mdev->matrix.adm);
+
+	kvm_get_kvm(matrix_mdev->kvm);
+	return 0;
+}
+
+/**
+ * vfio_ap_mdev_unset_kvm
+ *
+ * @matrix_mdev: a mediated matrix device
+ *
+ * - Clears the matrix masks inside the CRYCB
+ * - Reset the queues before to clear the hook in case IRQ happen during
+ *   reset.
+ * - Clears the hook
+ * - Decrement the KVM rerference count
+ */
+static int vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
+{
+	struct kvm *kvm = matrix_mdev->kvm;
+
+	kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
+	vfio_ap_mdev_reset_queues(matrix_mdev);
+	matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
+	matrix_mdev->kvm = NULL;
+	kvm_put_kvm(kvm);
+	return 0;
+}
+
 static int vfio_ap_mdev_open(struct mdev_device *mdev)
 {
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 	unsigned long events;
 	int ret;
 
+	mutex_lock(&matrix_dev->lock);
 
-	if (!try_module_get(THIS_MODULE))
-		return -ENODEV;
+	if (!try_module_get(THIS_MODULE)) {
+		ret = -ENODEV;
+		goto unlock;
+	}
 
 	matrix_mdev->group_notifier.notifier_call = vfio_ap_mdev_group_notifier;
 	events = VFIO_GROUP_NOTIFY_SET_KVM;
 
 	ret = vfio_register_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
 				     &events, &matrix_mdev->group_notifier);
-	if (ret) {
-		module_put(THIS_MODULE);
-		return ret;
+	if (ret)
+		goto put_unlock;
+
+	/* We do not support opening the mediated device without KVM */
+	if (!matrix_mdev->kvm) {
+		ret = -ENOENT;
+		goto free_notifier;
 	}
 
-	return 0;
+	ret = vfio_ap_mdev_set_kvm(matrix_mdev);
+	if (!ret)
+		goto unlock;
+
+free_notifier:
+	vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
+				 &matrix_mdev->group_notifier);
+put_unlock:
+	module_put(THIS_MODULE);
+unlock:
+	mutex_unlock(&matrix_dev->lock);
+	return ret;
 }
 
 static void vfio_ap_mdev_release(struct mdev_device *mdev)
 {
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 
-	if (matrix_mdev->kvm)
-		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
-
-	matrix_mdev->kvm = NULL;
-	vfio_ap_mdev_reset_queues(mdev);
+	mutex_lock(&matrix_dev->lock);
+	vfio_ap_mdev_unset_kvm(matrix_mdev);
 	vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
 				 &matrix_mdev->group_notifier);
 	module_put(THIS_MODULE);
+	mutex_unlock(&matrix_dev->lock);
 }
 
 static int vfio_ap_mdev_get_device_info(unsigned long arg)
@@ -939,7 +954,7 @@ static ssize_t vfio_ap_mdev_ioctl(struct mdev_device *mdev,
 		break;
 	case VFIO_DEVICE_RESET:
 		mutex_lock(&matrix_dev->lock);
-		ret = vfio_ap_mdev_reset_queues(mdev);
+		ret = vfio_ap_mdev_reset_queues(mdev_get_drvdata(mdev));
 		mutex_unlock(&matrix_dev->lock);
 		break;
 	default:
-- 
2.7.4