Re: [PATCH v4 13/15] KVM: s390: configure the guest's AP devices

From: Tony Krowiak
Date: Tue Apr 17 2018 - 12:36:47 EST

On 04/17/2018 12:18 PM, Pierre Morel wrote:
On 17/04/2018 18:08, Tony Krowiak wrote:
On 04/16/2018 09:05 AM, Pierre Morel wrote:
On 15/04/2018 23:22, Tony Krowiak wrote:
Registers a group notifier during the open of the mediated
matrix device to get information on KVM presence through the
VFIO_GROUP_NOTIFY_SET_KVM event. When notified, the pointer
to the kvm structure is saved inside the mediated matrix
device. Once the VFIO AP device driver has access to KVM,
access to the APs can be configured for the guest.

Access to APs is configured when the file descriptor for the
mediated matrix device is opened by userspace. The items to be
configured are:

1. The ECA.28 bit in the SIE state description determines whether
AP instructions are interpreted by the hardware or intercepted.
The VFIO AP device driver relies interpretive execution of
AP instructions so the ECA.28 bit will be set

2. Guest access to AP adapters, usage domains and control domains
is controlled by three bit masks referenced from the
Crypto Control Block (CRYCB) referenced from the guest's SIE state
description:

* The AP Mask (APM) controls access to the AP adapters. Each bit
in the APM represents an adapter number - from most significant
to least significant bit - from 0 to 255. The bits in the APM
are set according to the adapter numbers assigned to the mediated
matrix device via its 'assign_adapter' sysfs attribute file.

* The AP Queue (AQM) controls access to the AP queues. Each bit
in the AQM represents an AP queue index - from most significant
to least significant bit - from 0 to 255. A queue index references
a specific domain and is synonymous with the domian number. The
bits in the AQM are set according to the domain numbers assigned
to the mediated matrix device via its 'assign_domain' sysfs
attribute file.

* The AP Domain Mask (ADM) controls access to the AP control domains.
Each bit in the ADM represents a control domain - from most
significant to least significant bit - from 0-255. The
bits in the ADM are set according to the domain numbers assigned
to the mediated matrix device via its 'assign_control_domain'
sysfs attribute file.

Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx>
---
drivers/s390/crypto/vfio_ap_ops.c | 50 +++++++++++++++++++++++++++++++++
drivers/s390/crypto/vfio_ap_private.h | 2 +
2 files changed, 52 insertions(+), 0 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index bc2b05e..e3ff5ab 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -53,6 +53,54 @@ static int vfio_ap_mdev_remove(struct mdev_device *mdev)
return 0;
}

+static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct ap_matrix_mdev *matrix_mdev;
+
+ if (action == VFIO_GROUP_NOTIFY_SET_KVM) {
+ matrix_mdev = container_of(nb, struct ap_matrix_mdev,
+ group_notifier);
+ matrix_mdev->kvm = data;
+ }
+
+ 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;
+
+ 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)
+ return ret;
+
+ ret = kvm_ap_interpret_instructions(matrix_mdev->kvm, true);

Do you need this call ?
apie is always enabled in KVM if AP instructions are available.

I suppose we don't, in which case we don't need the kvm_ap_interpret_instructions()
function either ... at least not until we implement interception.



Setting or not the interpretation is done for the VM in a all.
It is not the right place to do it here since open is device dependent.

As I stated above, at this time we probably do not need this, however;
that will not always be the case. The setting is and always will be for the
VM in all - unless the architecture changes - because it is controlled by a
single bit (ECA.28). If you recall, I originally set interpretation in the
vfio_ap device driver when notified of the VFIO_GROUP_NOTIFY_SET_KVM event.
I believe ultimately that it is the device driver that should set the value
for apie.





Or we only have one device in the VM at a time.
In this case, shouldn't we make it official by returning -EEXIST for the second call?

We do allow only one vfio-ap device at a time. QEMU will allow only one vfio-ap device
to be configured for a guest. Should we also put a check in here?

QEMU is not the only possible user of this interface.

True .... I will put a check in here to make sure only one device is created.







+ if (ret)
+ return ret;
+
+ ret = kvm_ap_configure_matrix(matrix_mdev->kvm,
+ matrix_mdev->matrix);
+
+ return ret;
+}
+
+static void vfio_ap_mdev_release(struct mdev_device *mdev)
+{
+ struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
+
+ kvm_ap_deconfigure_matrix(matrix_mdev->kvm);
+ kvm_ap_interpret_instructions(matrix_mdev->kvm, false);

This call clears the apie in KVM.
This is only OK if we have a single device present until the end of the VM,
otherwise AP instructions in the guest will fail after the release until the end of the VM
or until a new device is plugged.

See Message ID: <1523819244-29954-5-git-send-email-akrowiak@xxxxxxxxxxxxxxxxxx> on the
qemu mailing list. There will be only one vfio-ap device allowed for the MVP model.

dito.
Anyone can write a userland application using this interface.

See comments above, not to mention I will probably remove this call.


<2b053349-071e-17ed-6ebd-a37bcfd2f330@xxxxxxxxxxxxxxxxxx>




+ vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
+ &matrix_mdev->group_notifier);
+}
+
static ssize_t name_show(struct kobject *kobj, struct device *dev, char *buf)
{
return sprintf(buf, "%s\n", VFIO_AP_MDEV_NAME_HWVIRT);
@@ -754,6 +802,8 @@ static ssize_t matrix_show(struct device *dev, struct device_attribute *attr,
.mdev_attr_groups = vfio_ap_mdev_attr_groups,
.create = vfio_ap_mdev_create,
.remove = vfio_ap_mdev_remove,
+ .open = vfio_ap_mdev_open,
+ .release = vfio_ap_mdev_release,
};

int vfio_ap_mdev_register(struct ap_matrix *ap_matrix)
diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
index f248faf..48e2806 100644
--- a/drivers/s390/crypto/vfio_ap_private.h
+++ b/drivers/s390/crypto/vfio_ap_private.h
@@ -31,6 +31,8 @@ struct ap_matrix {

struct ap_matrix_mdev {
struct kvm_ap_matrix *matrix;
+ struct notifier_block group_notifier;
+ struct kvm *kvm;
};

static inline struct ap_matrix *to_ap_matrix(struct device *dev)