Defines two new eventfd contexts for signaling userspace to enable and
disable vfio device migration. The IRQ indexes defined for these events are
defined in an enum in the include/uapi/linux/vfio.h header file:

VFIO_AP_ENABLE_MIG_IRQ_INDEX:  enable vfio device migration
VFIO_AP_DISABLE_MIG_IRQ_INDEX: disable vfio device migration

Information about those IRQs can be retrieved from userspace via the
VFIO_DEVICE_GET_IRQ_INFO ioctl. These events are initialized by the vfio_ap
device driver via the in response to the VFIO_DEVICE_SET_IRQ_INFO ioctl.
The eventfd for these IRQs will be signaled whenever the sysfs migratable
attribute of the mediated device is changed.

Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c     | 70 +++++++++++++++++++++++++--
 drivers/s390/crypto/vfio_ap_private.h |  6 +++
 include/uapi/linux/vfio.h             |  2 +
 3 files changed, 75 insertions(+), 3 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 97ec1f2fdbd1..213832263dc9 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -658,6 +658,18 @@ static void signal_guest_ap_cfg_changed(struct ap_matrix_mdev *matrix_mdev)
 		eventfd_signal(matrix_mdev->cfg_chg_trigger);
 }
 
+static void signal_enable_migration(struct ap_matrix_mdev *matrix_mdev)
+{
+	if (matrix_mdev->enable_mig_trigger)
+		eventfd_signal(matrix_mdev->enable_mig_trigger);
+}
+
+static void signal_disable_migration(struct ap_matrix_mdev *matrix_mdev)
+{
+	if (matrix_mdev->disable_mig_trigger)
+		eventfd_signal(matrix_mdev->disable_mig_trigger);
+}
+
 static void vfio_ap_mdev_update_guest_apcb(struct ap_matrix_mdev *matrix_mdev)
 {
 	if (matrix_mdev->kvm) {
@@ -805,6 +817,8 @@ static int vfio_ap_mdev_probe(struct mdev_device *mdev)
 	matrix_mdev->req_trigger = NULL;
 	matrix_mdev->cfg_chg_trigger = NULL;
 	matrix_mdev->migratable = VFIO_AP_DEVICE_MIGRATABLE_DEFAULT;
+	matrix_mdev->enable_mig_trigger = NULL;
+	matrix_mdev->disable_mig_trigger = NULL;
 	dev_set_drvdata(&mdev->dev, matrix_mdev);
 	mutex_lock(&matrix_dev->mdevs_lock);
 	list_add(&matrix_mdev->node, &matrix_dev->mdev_list);
@@ -1821,7 +1835,18 @@ static ssize_t migratable_store(struct device *dev, struct device_attribute *att
 		goto out_unlock;
 	}
 
+	if (matrix_mdev->migratable == migratable) {
+		ret = count;
+		goto out_unlock;
+	}
+
 	matrix_mdev->migratable = migratable;
+
+	if (matrix_mdev->migratable)
+		signal_enable_migration(matrix_mdev);
+	else
+		signal_disable_migration(matrix_mdev);
+
 	ret = count;
 out_unlock:
 	mutex_unlock(&matrix_dev->mdevs_lock);
@@ -2193,10 +2218,9 @@ static ssize_t vfio_ap_get_irq_info(unsigned long arg)
 
 	switch (info.index) {
 	case VFIO_AP_REQ_IRQ_INDEX:
-		info.count = 1;
-		info.flags = VFIO_IRQ_INFO_EVENTFD;
-		break;
 	case VFIO_AP_CFG_CHG_IRQ_INDEX:
+	case VFIO_AP_ENABLE_MIG_IRQ_INDEX:
+	case VFIO_AP_DISABLE_MIG_IRQ_INDEX:
 		info.count = 1;
 		info.flags = VFIO_IRQ_INFO_EVENTFD;
 		break;
@@ -2296,6 +2320,40 @@ static int vfio_ap_set_cfg_change_irq(struct ap_matrix_mdev *matrix_mdev, unsign
 	return 0;
 }
 
+static int vfio_ap_set_mig_irq(struct eventfd_ctx **mig_trigger,
+			       unsigned long arg)
+{
+	s32 fd;
+	void __user *data;
+	unsigned long minsz;
+	struct eventfd_ctx *mig_ctx;
+
+	minsz = offsetofend(struct vfio_irq_set, count);
+	data = (void __user *)(arg + minsz);
+
+	if (get_user(fd, (s32 __user *)data))
+		return -EFAULT;
+
+	if (fd == -1) {
+		if (*mig_trigger)
+			eventfd_ctx_put(*mig_trigger);
+		*mig_trigger = NULL;
+	} else if (fd >= 0) {
+		mig_ctx = eventfd_ctx_fdget(fd);
+		if (IS_ERR(mig_ctx))
+			return PTR_ERR(mig_ctx);
+
+		if (*mig_trigger)
+			eventfd_ctx_put(*mig_trigger);
+
+		*mig_trigger = mig_ctx;
+	} else {
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int vfio_ap_set_irqs(struct ap_matrix_mdev *matrix_mdev,
 			    unsigned long arg)
 {
@@ -2313,6 +2371,12 @@ static int vfio_ap_set_irqs(struct ap_matrix_mdev *matrix_mdev,
 			return vfio_ap_set_request_irq(matrix_mdev, arg);
 		case VFIO_AP_CFG_CHG_IRQ_INDEX:
 			return vfio_ap_set_cfg_change_irq(matrix_mdev, arg);
+		case VFIO_AP_ENABLE_MIG_IRQ_INDEX:
+			return vfio_ap_set_mig_irq(&matrix_mdev->enable_mig_trigger,
+						   arg);
+		case VFIO_AP_DISABLE_MIG_IRQ_INDEX:
+			return vfio_ap_set_mig_irq(&matrix_mdev->disable_mig_trigger,
+						   arg);
 		default:
 			return -EINVAL;
 		}
diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
index b75299c9c1d0..514de4a73678 100644
--- a/drivers/s390/crypto/vfio_ap_private.h
+++ b/drivers/s390/crypto/vfio_ap_private.h
@@ -108,6 +108,10 @@ struct ap_queue_table {
  *		migrated (1) or not (0)
  * @req_trigger eventfd ctx for signaling userspace to return a device
  * @cfg_chg_trigger eventfd ctx to signal AP config changed to userspace
+ * @enable_mig_trigger:  eventfd ctx to signal userspace to enable vfio device
+ *			 migration
+ * @disable_mig_trigger: eventfd ctx to signal userspace to disable vfio device
+ *			 migration
  * @apm_add:	bitmap of APIDs added to the host's AP configuration
  * @aqm_add:	bitmap of APQIs added to the host's AP configuration
  * @adm_add:	bitmap of control domain numbers added to the host's AP
@@ -125,6 +129,8 @@ struct ap_matrix_mdev {
 	int    migratable;
 	struct eventfd_ctx *req_trigger;
 	struct eventfd_ctx *cfg_chg_trigger;
+	struct eventfd_ctx *enable_mig_trigger;
+	struct eventfd_ctx *disable_mig_trigger;
 	DECLARE_BITMAP(apm_add, AP_DEVICES);
 	DECLARE_BITMAP(aqm_add, AP_DOMAINS);
 	DECLARE_BITMAP(adm_add, AP_DOMAINS);
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index bb7b89330d35..c661b8b22ead 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -673,6 +673,8 @@ enum {
 enum {
 	VFIO_AP_REQ_IRQ_INDEX,
 	VFIO_AP_CFG_CHG_IRQ_INDEX,
+	VFIO_AP_ENABLE_MIG_IRQ_INDEX,
+	VFIO_AP_DISABLE_MIG_IRQ_INDEX,
 	VFIO_AP_NUM_IRQS
 };
 
-- 
2.52.0