Re: [PATCH v10 11/26] s390: vfio-ap: implement mediated device open callback

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On 09/12/2018 03:43 PM, Tony Krowiak wrote:
From: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>

Implements the open callback on the mediated matrix device.
The function registers a group notifier to receive notification
of the VFIO_GROUP_NOTIFY_SET_KVM event. When notified,
the vfio_ap device driver will get access to the guest's
kvm structure. The open callback must ensure that only one
mediated device shall be opened per guest.

Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
Acked-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
Tested-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
Tested-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
Tested-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
Acked-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
  arch/s390/include/asm/kvm_host.h      |    1 +
  drivers/s390/crypto/vfio_ap_ops.c     |  168 +++++++++++++++++++++++++++++++++
  drivers/s390/crypto/vfio_ap_private.h |    5 +
  3 files changed, 174 insertions(+), 0 deletions(-)


(...)

@@ -699,12 +730,149 @@ static ssize_t matrix_show(struct device *dev, struct device_attribute *attr,
  	NULL
  };
+/**
+ * Verify that the AP instructions are available on the guest. This is indicated
+ * via the  KVM_S390_VM_CPU_FEAT_AP CPU model feature.
+ */
+static int kvm_ap_validate_crypto_setup(struct kvm *kvm)
+{
+	if (test_bit_inv(KVM_S390_VM_CPU_FEAT_AP, kvm->arch.cpu_feat))
+		return 0;
+
+	return -EOPNOTSUPP;
+}
+

(...)

+
+/**
+ * vfio_ap_mdev_open_once
+ *
+ * @matrix_mdev: a mediated matrix device
+ *
+ * Return 0 if no other mediated matrix device has been opened for the
+ * KVM guest assigned to @matrix_mdev; otherwise, returns an error.
+ */
+static int vfio_ap_mdev_open_once(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;
+		}
+	}
+
+	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_open_once(matrix_mdev, data);
+	if (ret)
+		return NOTIFY_DONE;
+
+	matrix_mdev->kvm = data;
+
+	ret = kvm_ap_validate_crypto_setup(matrix_mdev->kvm);
+	if (ret)
+		return ret;
+
+	vfio_ap_mdev_copy_masks(matrix_mdev);
+
+	return NOTIFY_OK;
+}
+
+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;
+
+
+	if (!try_module_get(THIS_MODULE))
+		return -ENODEV;
+
+	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;
+	}
+
+	return 0;
+}
+

(...)

The fixup! patch below modifies this patch (11/26) to illustrate how
David's recommendation will be implemented for v11 of the series. It
is one of three fixup! patches (the other two are in responses to
03/26 and 25/26) included to generate discussion in v10 rather than
waiting until v11 for comments.

-----------------------------------8<-----------------------------------

From: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
Date: Thu, 20 Sep 2018 12:01:53 -0400
Subject: [FIXUP v10] fixup!: s390: vfio-ap: implement mediated device open callback

* Fix race condition in KVM notifier
* Remove test for KVM_S390_VM_CPU_FEAT_AP
---
 drivers/s390/crypto/vfio_ap_ops.c |   26 +++++++++++++++-----------
 1 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 8bc0cdd..573a5cc 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -731,12 +731,12 @@ static ssize_t matrix_show(struct device *dev, struct device_attribute *attr,
 };

 /**
- * Verify that the AP instructions are available on the guest. This is indicated
- * via the  KVM_S390_VM_CPU_FEAT_AP CPU model feature.
+ * Verify that the AP instructions are being interpreted by firmware for the
+ * guest. This is indicated by the kvm->arch.crypto.apie flag.
  */
 static int kvm_ap_validate_crypto_setup(struct kvm *kvm)
 {
-	if (test_bit_inv(KVM_S390_VM_CPU_FEAT_AP, kvm->arch.cpu_feat))
+	if (kvm->arch.crypto.apie)
 		return 0;

 	return -EOPNOTSUPP;
@@ -772,15 +772,19 @@ static void vfio_ap_mdev_copy_masks(struct ap_matrix_mdev *matrix_mdev)
 }

 /**
- * vfio_ap_mdev_open_once
+ * vfio_ap_mdev_set_kvm
  *
  * @matrix_mdev: a mediated matrix device
+ * @kvm: reference to KVM instance
  *
- * Return 0 if no other mediated matrix device has been opened for the
- * KVM guest assigned to @matrix_mdev; otherwise, returns an error.
+ * Verifies no other mediated matrix device has a reference to @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 -EPERM.
  */
-static int vfio_ap_mdev_open_once(struct ap_matrix_mdev *matrix_mdev,
-				  struct kvm *kvm)
+static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
+				struct kvm *kvm)
 {
 	struct ap_matrix_mdev *m;

@@ -793,6 +797,7 @@ static int vfio_ap_mdev_open_once(struct ap_matrix_mdev *matrix_mdev,
 		}
 	}

+	matrix_mdev->kvm = kvm;
 	mutex_unlock(&matrix_dev->lock);

 	return 0;
@@ -814,16 +819,15 @@ static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
 		return NOTIFY_OK;
 	}

-	ret = vfio_ap_mdev_open_once(matrix_mdev, data);
+	ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
 	if (ret)
 		return NOTIFY_DONE;

-	matrix_mdev->kvm = data;
-
 	ret = kvm_ap_validate_crypto_setup(matrix_mdev->kvm);
 	if (ret)
 		return ret;

+
 	vfio_ap_mdev_copy_masks(matrix_mdev);

 	return NOTIFY_OK;
--
1.7.1




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