[PATCH v2 2/2] s390/vfio-ap: reverse group notifier actions when KVM pointer invalidated

[Tony Krowiak <akrowiak@xxxxxxxxxxxxx>]

The vfio_ap device driver registers a group notifier with VFIO when the
file descriptor for a VFIO mediated device for a KVM guest is opened to
receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
event). When the KVM pointer is set, the vfio_ap driver takes the
following actions:
1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
   of the mediated device.
2. Calls the kvm_get_kvm() function to increment its reference counter.
3. Sets the function pointer to the function that handles interception of
   the instruction that enables/disables interrupt processing.

When the notifier is called to make notification that the KVM pointer has
been set to NULL, the driver should reverse the actions taken when the
KVM pointer was set as well as unplugging the AP devices passed through
to the KVM guest.

Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
---
 drivers/s390/crypto/vfio_ap_ops.c | 40 ++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index c854d7ab2079..1c3c2a0898b9 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -1033,8 +1033,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
 {
 	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);
@@ -1045,7 +1043,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
 	matrix_mdev->kvm = kvm;
 	kvm_get_kvm(kvm);
 	kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
-	mutex_unlock(&matrix_dev->lock);
 
 	return 0;
 }
@@ -1079,35 +1076,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
 	return NOTIFY_DONE;
 }
 
+static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
+{
+	kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
+	matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
+	vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
+	kvm_put_kvm(matrix_mdev->kvm);
+	matrix_mdev->kvm = NULL;
+}
+
 static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
 				       unsigned long action, void *data)
 {
-	int ret;
+	int ret, notify_rc = NOTIFY_DONE;
 	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);
+	mutex_lock(&matrix_dev->lock);
 
 	if (!data) {
-		matrix_mdev->kvm = NULL;
-		return NOTIFY_OK;
+		if (matrix_mdev->kvm)
+			vfio_ap_mdev_unset_kvm(matrix_mdev);
+		notify_rc = NOTIFY_OK;
+		goto notify_done;
 	}
 
 	ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
 	if (ret)
-		return NOTIFY_DONE;
+		goto 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;
+		goto notify_done;
 
 	kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
 				  matrix_mdev->matrix.aqm,
 				  matrix_mdev->matrix.adm);
 
-	return NOTIFY_OK;
+notify_done:
+	mutex_unlock(&matrix_dev->lock);
+	return notify_rc;
 }
 
 static struct vfio_ap_queue *vfio_ap_find_queue(int apqn)
@@ -1234,13 +1245,10 @@ static void vfio_ap_mdev_release(struct mdev_device *mdev)
 	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
 
 	mutex_lock(&matrix_dev->lock);
-	if (matrix_mdev->kvm) {
-		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
-		matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
-		vfio_ap_mdev_reset_queues(mdev);
-		kvm_put_kvm(matrix_mdev->kvm);
-		matrix_mdev->kvm = NULL;
-	}
+	if (matrix_mdev->kvm)
+		vfio_ap_mdev_unset_kvm(matrix_mdev);
+	else
+		vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
 	mutex_unlock(&matrix_dev->lock);
 
 	vfio_unregister_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY,
-- 
2.21.1