[PATCH v2 03/19] iommu: introduce device fault report API

[Jacob Pan]

Traditionally, device specific faults are detected and handled within
their own device drivers. When IOMMU is enabled, faults such as DMA
related transactions are detected by IOMMU. There is no generic
reporting mechanism to report faults back to the in-kernel device
driver or the guest OS in case of assigned devices.

This patch introduces a registration API for device specific fault
handlers. This differs from the existing iommu_set_fault_handler/
report_iommu_fault infrastructures in several ways:
- it allows to report more sophisticated fault events (both
  unrecoverable faults and page request faults) due to the nature
  of the iommu_fault struct
- it is device specific and not domain specific.

The current iommu_report_device_fault() implementation only handles
the "shoot and forget" unrecoverable fault case. Handling of page
request faults or stalled faults will come later.

Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>

---
v6 -> v7:
- use struct iommu_param *param = dev->iommu_param;

v4 -> v5:
- remove stuff related to recoverable faults
---
 drivers/iommu/iommu.c | 135 +++++++++++++++++++++++++++++++++++++++++++++++++-
 include/linux/iommu.h |  36 +++++++++++++-
 2 files changed, 169 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index f8fe112..75c352c 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -648,6 +648,13 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
 		goto err_free_name;
 	}
 
+	dev->iommu_param = kzalloc(sizeof(*dev->iommu_param), GFP_KERNEL);
+	if (!dev->iommu_param) {
+		ret = -ENOMEM;
+		goto err_free_name;
+	}
+	mutex_init(&dev->iommu_param->lock);
+
 	kobject_get(group->devices_kobj);
 
 	dev->iommu_group = group;
@@ -678,6 +685,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
 	mutex_unlock(&group->mutex);
 	dev->iommu_group = NULL;
 	kobject_put(group->devices_kobj);
+	kfree(dev->iommu_param);
 err_free_name:
 	kfree(device->name);
 err_remove_link:
@@ -724,7 +732,7 @@ void iommu_group_remove_device(struct device *dev)
 	sysfs_remove_link(&dev->kobj, "iommu_group");
 
 	trace_remove_device_from_group(group->id, dev);
-
+	kfree(dev->iommu_param);
 	kfree(device->name);
 	kfree(device);
 	dev->iommu_group = NULL;
@@ -859,6 +867,131 @@ int iommu_group_unregister_notifier(struct iommu_group *group,
 EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier);
 
 /**
+ * iommu_register_device_fault_handler() - Register a device fault handler
+ * @dev: the device
+ * @handler: the fault handler
+ * @data: private data passed as argument to the handler
+ *
+ * When an IOMMU fault event is received, this handler gets called with the
+ * fault event and data as argument.
+ *
+ * Return 0 if the fault handler was installed successfully, or an error.
+ */
+int iommu_register_device_fault_handler(struct device *dev,
+					iommu_dev_fault_handler_t handler,
+					void *data)
+{
+	struct iommu_param *param = dev->iommu_param;
+	int ret = 0;
+
+	/*
+	 * Device iommu_param should have been allocated when device is
+	 * added to its iommu_group.
+	 */
+	if (!param)
+		return -EINVAL;
+
+	mutex_lock(&param->lock);
+	/* Only allow one fault handler registered for each device */
+	if (param->fault_param) {
+		ret = -EBUSY;
+		goto done_unlock;
+	}
+
+	get_device(dev);
+	param->fault_param =
+		kzalloc(sizeof(struct iommu_fault_param), GFP_KERNEL);
+	if (!param->fault_param) {
+		put_device(dev);
+		ret = -ENOMEM;
+		goto done_unlock;
+	}
+	mutex_init(&param->fault_param->lock);
+	param->fault_param->handler = handler;
+	param->fault_param->data = data;
+	INIT_LIST_HEAD(&param->fault_param->faults);
+
+done_unlock:
+	mutex_unlock(&param->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iommu_register_device_fault_handler);
+
+/**
+ * iommu_unregister_device_fault_handler() - Unregister the device fault handler
+ * @dev: the device
+ *
+ * Remove the device fault handler installed with
+ * iommu_register_device_fault_handler().
+ *
+ * Return 0 on success, or an error.
+ */
+int iommu_unregister_device_fault_handler(struct device *dev)
+{
+	struct iommu_param *param = dev->iommu_param;
+	int ret = 0;
+
+	if (!param)
+		return -EINVAL;
+
+	mutex_lock(&param->lock);
+
+	if (!param->fault_param)
+		goto unlock;
+
+	/* we cannot unregister handler if there are pending faults */
+	if (!list_empty(&param->fault_param->faults)) {
+		ret = -EBUSY;
+		goto unlock;
+	}
+
+	kfree(param->fault_param);
+	param->fault_param = NULL;
+	put_device(dev);
+unlock:
+	mutex_unlock(&param->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iommu_unregister_device_fault_handler);
+
+
+/**
+ * iommu_report_device_fault() - Report fault event to device
+ * @dev: the device
+ * @evt: fault event data
+ *
+ * Called by IOMMU model specific drivers when fault is detected, typically
+ * in a threaded IRQ handler.
+ *
+ * Return 0 on success, or an error.
+ */
+int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
+{
+	struct iommu_param *param = dev->iommu_param;
+	struct iommu_fault_param *fparam;
+	int ret = 0;
+
+	/* iommu_param is allocated when device is added to group */
+	if (!param || !evt)
+		return -EINVAL;
+
+	/* we only report device fault if there is a handler registered */
+	mutex_lock(&param->lock);
+	fparam = param->fault_param;
+	if (!fparam || !fparam->handler) {
+		ret = -EINVAL;
+		goto done_unlock;
+	}
+	ret = fparam->handler(evt, fparam->data);
+done_unlock:
+	mutex_unlock(&param->lock);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iommu_report_device_fault);
+
+/**
  * iommu_group_id - Return ID for a group
  * @group: the group to ID
  *
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 810bde2..a42019a 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -311,11 +311,13 @@ struct iommu_device {
  * unrecoverable faults such as DMA or IRQ remapping faults.
  *
  * @fault: fault descriptor
+ * @list pending fault event list, used for tracking responses
  * @iommu_private: used by the IOMMU driver for storing fault-specific
  *                 data. Users should not modify this field before
  *                 sending the fault response.
  */
 struct iommu_fault_event {
+	struct list_head list;
 	struct iommu_fault fault;
 	u64 iommu_private;
 };
@@ -324,10 +326,13 @@ struct iommu_fault_event {
  * struct iommu_fault_param - per-device IOMMU fault data
  * @dev_fault_handler: Callback function to handle IOMMU faults at device level
  * @data: handler private data
- *
+ * @faults: holds the pending faults which needs response, e.g. page response.
+ * @lock: protect pending PRQ event list
  */
 struct iommu_fault_param {
 	iommu_dev_fault_handler_t handler;
+	struct list_head faults;
+	struct mutex lock;
 	void *data;
 };
 
@@ -341,6 +346,7 @@ struct iommu_fault_param {
  *	struct iommu_fwspec	*iommu_fwspec;
  */
 struct iommu_param {
+	struct mutex lock;
 	struct iommu_fault_param *fault_param;
 };
 
@@ -433,6 +439,15 @@ extern int iommu_group_register_notifier(struct iommu_group *group,
 					 struct notifier_block *nb);
 extern int iommu_group_unregister_notifier(struct iommu_group *group,
 					   struct notifier_block *nb);
+extern int iommu_register_device_fault_handler(struct device *dev,
+					iommu_dev_fault_handler_t handler,
+					void *data);
+
+extern int iommu_unregister_device_fault_handler(struct device *dev);
+
+extern int iommu_report_device_fault(struct device *dev,
+				     struct iommu_fault_event *evt);
+
 extern int iommu_group_id(struct iommu_group *group);
 extern struct iommu_group *iommu_group_get_for_dev(struct device *dev);
 extern struct iommu_domain *iommu_group_default_domain(struct iommu_group *);
@@ -737,6 +752,25 @@ static inline int iommu_group_unregister_notifier(struct iommu_group *group,
 	return 0;
 }
 
+static inline
+int iommu_register_device_fault_handler(struct device *dev,
+					iommu_dev_fault_handler_t handler,
+					void *data)
+{
+	return -ENODEV;
+}
+
+static inline int iommu_unregister_device_fault_handler(struct device *dev)
+{
+	return 0;
+}
+
+static inline
+int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
+{
+	return -ENODEV;
+}
+
 static inline int iommu_group_id(struct iommu_group *group)
 {
 	return -ENODEV;
-- 
2.7.4