[PATCH v10 15/16] s390/vfio-ap: handle probe/remove not due to host AP config changes

Tony Krowiak
2020-08-21T19:56:55Z

AP queue devices are probed or removed for reasons other than changes
to the host AP configuration. For example:

* The state of an AP adapter can be dynamically changed from standby to
online via the SE or by execution of the SCLP Configure AP command. When
the state changes, each queue device associated with the card device
representing the adapter will get created and probed.

* The state of an AP adapter can be dynamically changed from online to
standby via the SE or by execution of the SCLP Deconfigure AP command.
When the state changes, each queue device associated with the card device
representing the adapter will get removed.

* Each queue device associated with a card device will get removed
when the type of the AP adapter represented by the card device
dynamically changes.

* Each queue device associated with a card device will get removed
when the status of the queue represented by the queue device changes
from operating to check stop.

* AP queue devices can be manually bound to or unbound from the vfio_ap
device driver by a root user via the sysfs bind/unbind attributes of the
driver.

In response to a queue device probe or remove that is not the result of a
change to the host's AP configuration, if a KVM guest is using the matrix
mdev to which the APQN of the queue device is assigned, the vfio_ap device
driver must respond accordingly. In an ideal world, the queue device being
probed would be hot plugged into the guest. Likewise, the queue
corresponding to the queue device being removed would
be hot unplugged from the guest. Unfortunately, the AP architecture
precludes plugging or unplugging individual queues, so let's handle
the probe or remove of an AP queue device as follows:

Handling Probe
--------------
There are two requirements that must be met in order to give a
guest access to the queue corresponding to the queue device being probed:

* Each APQN derived from the APID of the queue device and the APQIs of the
domains already assigned to the guest's AP configuration must reference
a queue device bound to the vfio_ap device driver.

* Each APQN derived from the APQI of the queue device and the APIDs of the
adapters assigned to the guest's AP configuration must reference a queue
device bound to the vfio_ap device driver.

If the above conditions are met, the APQN will be assigned to the guest's
AP configuration and the guest will be given access to the queue.

Handling Remove
---------------
Since the AP architecture precludes us from taking access to an individual
queue from a guest, we are left with the choice of taking access away from
either the adapter or the domain to which the queue is connected. Access to
the adapter will be taken away because it is likely that most of the time,
the remove callback will be invoked because the adapter state has
transitioned from online to standby. In such a case, no queue connected
to the adapter will be available to access.

Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
---
drivers/s390/crypto/vfio_ap_ops.c | 84 +++++++++++++++++++++++++++++++
1 file changed, 84 insertions(+)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index e6480f31a42b..b6a1e280991d 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -1682,6 +1682,61 @@ static void vfio_ap_queue_link_mdev(struct vfio_ap_queue *q)
}
}

+static bool vfio_ap_mdev_assign_shadow_apid(struct ap_matrix_mdev *matrix_mdev,
+ unsigned long apid)
+{
+ unsigned long apqi;
+
+ for_each_set_bit_inv(apqi, matrix_mdev->shadow_apcb.aqm,
+ matrix_mdev->shadow_apcb.aqm_max + 1) {
+ if (!vfio_ap_get_queue(AP_MKQID(apid, apqi)))
+ return false;
+ }
+
+ set_bit_inv(apid, matrix_mdev->shadow_apcb.apm);
+
+ return true;
+}
+
+static bool vfio_ap_mdev_assign_shadow_apqi(struct ap_matrix_mdev *matrix_mdev,
+ unsigned long apqi)
+{
+ unsigned long apid;
+
+ for_each_set_bit_inv(apid, matrix_mdev->shadow_apcb.apm,
+ matrix_mdev->shadow_apcb.apm_max + 1) {
+ if (!vfio_ap_get_queue(AP_MKQID(apid, apqi)))
+ return false;
+ }
+
+ set_bit_inv(apqi, matrix_mdev->shadow_apcb.aqm);
+
+ return true;
+}
+
+static void vfio_ap_mdev_hot_plug_queue(struct vfio_ap_queue *q)
+{
+ bool commit = false;
+ unsigned long apid = AP_QID_CARD(q->apqn);
+ unsigned long apqi = AP_QID_QUEUE(q->apqn);
+
+ if ((q->matrix_mdev == NULL) || !vfio_ap_mdev_has_crycb(q->matrix_mdev))
+ return;
+
+ if (!test_bit_inv(apid, q->matrix_mdev->matrix.apm) ||
+ !test_bit_inv(apqi, q->matrix_mdev->matrix.aqm))
+ return;
+
+ if (!test_bit_inv(apid, q->matrix_mdev->shadow_apcb.apm))
+ commit |= vfio_ap_mdev_assign_shadow_apid(q->matrix_mdev, apid);
+
+ if (!test_bit_inv(apqi, q->matrix_mdev->shadow_apcb.aqm))
+ commit |= vfio_ap_mdev_assign_shadow_apqi(q->matrix_mdev, apqi);
+
+ if (commit)
+ vfio_ap_mdev_commit_shadow_apcb(q->matrix_mdev);
+}
+
int vfio_ap_mdev_probe_queue(struct ap_queue *queue)
{
struct vfio_ap_queue *q;
@@ -1695,11 +1750,35 @@ int vfio_ap_mdev_probe_queue(struct ap_queue *queue)
q->apqn = queue->qid;
q->saved_isc = VFIO_AP_ISC_INVALID;
vfio_ap_queue_link_mdev(q);
+ /* Make sure we're not in the middle of an AP configuration change. */
+ if (!(matrix_dev->flags & AP_MATRIX_CFG_CHG))
+ vfio_ap_mdev_hot_plug_queue(q);
mutex_unlock(&matrix_dev->lock);

return 0;
}

+void vfio_ap_mdev_hot_unplug_queue(struct vfio_ap_queue *q)
+{
+ unsigned long apid = AP_QID_CARD(q->apqn);
+ unsigned long apqi = AP_QID_QUEUE(q->apqn);
+
+ if ((q->matrix_mdev == NULL) || !vfio_ap_mdev_has_crycb(q->matrix_mdev))
+ return;
+
+ /*
+ * If the APQN is assigned to the guest, then let's
+ * go ahead and unplug the adapter since the
+ * architecture does not provide a means to unplug
+ * an individual queue.
+ */
+ if (test_bit_inv(apid, q->matrix_mdev->shadow_apcb.apm) &&
+ test_bit_inv(apqi, q->matrix_mdev->shadow_apcb.aqm)) {
+ if (vfio_ap_mdev_unassign_guest_apid(q->matrix_mdev, apid))
+ vfio_ap_mdev_commit_shadow_apcb(q->matrix_mdev);
+ }
+}
+
void vfio_ap_mdev_remove_queue(struct ap_queue *queue)
{
struct vfio_ap_queue *q;
@@ -1707,6 +1786,11 @@ void vfio_ap_mdev_remove_queue(struct ap_queue *queue)

mutex_lock(&matrix_dev->lock);
q = dev_get_drvdata(&queue->ap_dev.device);
+
+ /* Make sure we're not in the middle of an AP configuration change. */
+ if (!(matrix_dev->flags & AP_MATRIX_CFG_CHG))
+ vfio_ap_mdev_hot_unplug_queue(q);
+
dev_set_drvdata(&queue->ap_dev.device, NULL);
apid = AP_QID_CARD(q->apqn);
apqi = AP_QID_QUEUE(q->apqn);
--
2.21.1