Re: [PATCH v4 03/22] iommu: Introduce device fault report API
On Sun, 9 Jun 2019 06:44:03 -0700
Jacob Pan wrote:
> 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
> Signed-off-by: Ashok Raj
> Signed-off-by: Jean-Philippe Brucker
> Signed-off-by: Eric Auger
A few nitpicks and minor suggestions inline.
> ---
> drivers/iommu/iommu.c | 127
> +-
> include/linux/iommu.h | 33 -
> 2 files changed, 157 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 67ee662..7955184 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -644,6 +644,13 @@ 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(>iommu_param->lock);
> +
> kobject_get(group->devices_kobj);
>
> dev->iommu_group = group;
> @@ -674,6 +681,7 @@ int iommu_group_add_device(struct iommu_group *group,
> struct device *dev)
> mutex_unlock(>mutex);
> dev->iommu_group = NULL;
> kobject_put(group->devices_kobj);
> + kfree(dev->iommu_param);
> err_free_name:
> kfree(device->name);
> err_remove_link:
> @@ -720,7 +728,7 @@ void iommu_group_remove_device(struct device *dev)
> sysfs_remove_link(>kobj, "iommu_group");
>
> trace_remove_device_from_group(group->id, dev);
> -
> + kfree(dev->iommu_param);
> kfree(device->name);
> kfree(device);
> dev->iommu_group = NULL;
> @@ -855,6 +863,123 @@ 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(>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;
> + }
> + param->fault_param->handler = handler;
> + param->fault_param->data = data;
> +
> +done_unlock:
> + mutex_unlock(>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(>lock);
> +
> + if (!param->fault_param)
> + goto unlock;
> +
> + kfree(param->fault_param);
> + param->fault_param = NULL;
> + put_device(dev);
> +unlock:
> +
[PATCH v4 03/22] iommu: Introduce device fault report API
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
Signed-off-by: Ashok Raj
Signed-off-by: Jean-Philippe Brucker
Signed-off-by: Eric Auger
---
drivers/iommu/iommu.c | 127 +-
include/linux/iommu.h | 33 -
2 files changed, 157 insertions(+), 3 deletions(-)
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 67ee662..7955184 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -644,6 +644,13 @@ 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(>iommu_param->lock);
+
kobject_get(group->devices_kobj);
dev->iommu_group = group;
@@ -674,6 +681,7 @@ int iommu_group_add_device(struct iommu_group *group,
struct device *dev)
mutex_unlock(>mutex);
dev->iommu_group = NULL;
kobject_put(group->devices_kobj);
+ kfree(dev->iommu_param);
err_free_name:
kfree(device->name);
err_remove_link:
@@ -720,7 +728,7 @@ void iommu_group_remove_device(struct device *dev)
sysfs_remove_link(>kobj, "iommu_group");
trace_remove_device_from_group(group->id, dev);
-
+ kfree(dev->iommu_param);
kfree(device->name);
kfree(device);
dev->iommu_group = NULL;
@@ -855,6 +863,123 @@ 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(>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;
+ }
+ param->fault_param->handler = handler;
+ param->fault_param->data = data;
+
+done_unlock:
+ mutex_unlock(>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(>lock);
+
+ if (!param->fault_param)
+ goto unlock;
+
+ kfree(param->fault_param);
+ param->fault_param = NULL;
+ put_device(dev);
+unlock:
+ mutex_unlock(>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 drivers when a fault is
Re: [PATCH v4 03/22] iommu: introduce device fault report API
On 06/03/2019 23:46, Jacob Pan wrote:
> On Tue, 5 Mar 2019 15:03:41 +
> Jean-Philippe Brucker wrote:
>
>> On 18/02/2019 13:54, Eric Auger wrote:
>> [...]> +/**
>> > + * 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, call this handler with
>> > the fault event
>> > + * and data as argument. The handler should return 0 on success.
>> > If the fault is
>> > + * recoverable (IOMMU_FAULT_PAGE_REQ), the handler can also
>> > complete
>> > + * the fault by calling iommu_page_response() with one of the
>> > following
>> > + * response code:
>> > + * - IOMMU_PAGE_RESP_SUCCESS: retry the translation
>> > + * - IOMMU_PAGE_RESP_INVALID: terminate the fault
>> > + * - IOMMU_PAGE_RESP_FAILURE: terminate the fault and stop
>> > reporting
>> > + * page faults if possible.
>>
>> The comment refers to function and values that haven't been defined
>> yet. Either the page_response() patch should come before, or we need
>> to split this patch.
>>
>> Something I missed before: if the handler fails (returns != 0) it
>> should complete the fault by calling iommu_page_response(), if we're
>> not doing it in iommu_report_device_fault(). It should be indicated
>> in this comment. It's safe for the handler to call page_response()
>> since we're not holding fault_param->lock when calling the handler.
>>
> If the page request fault is to be reported to a guest, the report
> function cannot wait for the completion status. As long as the fault is
> injected into the guest, the handler should complete with success. If
> the PRQ report fails, IMHO, the caller of iommu_report_device_fault()
> should send page_response, perhaps after clean up all partial response
> of the group too.
Ok, the caller (IOMMU driver) sending the page_response if
iommu_report_device_fault() fails does make more sense. Agreed on the
partial cleanup as well, we don't keep track of them here, but I need to
add that to the io-pgfault layer. However some cleanup should probably
happen in here...
>> > + /* we only report device fault if there is a handler
>> > registered */
>> > + mutex_lock(>iommu_param->lock);
>> > + if (!dev->iommu_param->fault_param ||
>> > + !dev->iommu_param->fault_param->handler) {
>> > + ret = -EINVAL;
>> > + goto done_unlock;
>> > + }
>> > + fparam = dev->iommu_param->fault_param;
>> > + if (evt->fault.type == IOMMU_FAULT_PAGE_REQ &&
>> > + evt->fault.prm.flags &
>> > IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE) {
>> > + evt_pending = kmemdup(evt, sizeof(struct
>> > iommu_fault_event),
>> > + GFP_KERNEL);
>> > + if (!evt_pending) {
>> > + ret = -ENOMEM;
>> > + goto done_unlock;
>> > + }
>> > + mutex_lock(>lock);
>> > + list_add_tail(_pending->list, >faults);
>> > + mutex_unlock(>lock);
>> > + }
>> > + ret = fparam->handler(evt, fparam->data);
... if ret != 0, removing and freeing the pending event seems more
appropriate here than asking our caller to do it
Thanks,
Jean
>> > +done_unlock:
>> > + mutex_unlock(>iommu_param->lock);
>> > + return ret;
>> > +}
>> > +EXPORT_SYMBOL_GPL(iommu_report_device_fault);
>> [...]
>
> [Jacob Pan]
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Re: [PATCH v4 03/22] iommu: introduce device fault report API
On Tue, 5 Mar 2019 15:03:41 +
Jean-Philippe Brucker wrote:
> On 18/02/2019 13:54, Eric Auger wrote:
> [...]> +/**
> > + * 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, call this handler with
> > the fault event
> > + * and data as argument. The handler should return 0 on success.
> > If the fault is
> > + * recoverable (IOMMU_FAULT_PAGE_REQ), the handler can also
> > complete
> > + * the fault by calling iommu_page_response() with one of the
> > following
> > + * response code:
> > + * - IOMMU_PAGE_RESP_SUCCESS: retry the translation
> > + * - IOMMU_PAGE_RESP_INVALID: terminate the fault
> > + * - IOMMU_PAGE_RESP_FAILURE: terminate the fault and stop
> > reporting
> > + * page faults if possible.
>
> The comment refers to function and values that haven't been defined
> yet. Either the page_response() patch should come before, or we need
> to split this patch.
>
> Something I missed before: if the handler fails (returns != 0) it
> should complete the fault by calling iommu_page_response(), if we're
> not doing it in iommu_report_device_fault(). It should be indicated
> in this comment. It's safe for the handler to call page_response()
> since we're not holding fault_param->lock when calling the handler.
>
If the page request fault is to be reported to a guest, the report
function cannot wait for the completion status. As long as the fault is
injected into the guest, the handler should complete with success. If
the PRQ report fails, IMHO, the caller of iommu_report_device_fault()
should send page_response, perhaps after clean up all partial response
of the group too.
> > + *
> > + * Return 0 if the fault handler was installed successfully, or an
> > error.
> > + */
> [...]
> > +/**
> > + * 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) +{
> > + int ret = 0;
> > + struct iommu_fault_event *evt_pending;
> > + struct iommu_fault_param *fparam;
> > +
> > + /* iommu_param is allocated when device is added to group
> > */
> > + if (!dev->iommu_param | !evt)
>
> Typo: ||
>
> Thanks,
> Jean
>
> > + return -EINVAL;
> > + /* we only report device fault if there is a handler
> > registered */
> > + mutex_lock(>iommu_param->lock);
> > + if (!dev->iommu_param->fault_param ||
> > + !dev->iommu_param->fault_param->handler) {
> > + ret = -EINVAL;
> > + goto done_unlock;
> > + }
> > + fparam = dev->iommu_param->fault_param;
> > + if (evt->fault.type == IOMMU_FAULT_PAGE_REQ &&
> > + evt->fault.prm.flags &
> > IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE) {
> > + evt_pending = kmemdup(evt, sizeof(struct
> > iommu_fault_event),
> > + GFP_KERNEL);
> > + if (!evt_pending) {
> > + ret = -ENOMEM;
> > + goto done_unlock;
> > + }
> > + mutex_lock(>lock);
> > + list_add_tail(_pending->list, >faults);
> > + mutex_unlock(>lock);
> > + }
> > + ret = fparam->handler(evt, fparam->data);
> > +done_unlock:
> > + mutex_unlock(>iommu_param->lock);
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(iommu_report_device_fault);
> [...]
[Jacob Pan]
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Re: [PATCH v4 03/22] iommu: introduce device fault report API
On 18/02/2019 13:54, Eric Auger wrote:
[...]> +/**
> + * 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, call this handler with the fault
> event
> + * and data as argument. The handler should return 0 on success. If the
> fault is
> + * recoverable (IOMMU_FAULT_PAGE_REQ), the handler can also complete
> + * the fault by calling iommu_page_response() with one of the following
> + * response code:
> + * - IOMMU_PAGE_RESP_SUCCESS: retry the translation
> + * - IOMMU_PAGE_RESP_INVALID: terminate the fault
> + * - IOMMU_PAGE_RESP_FAILURE: terminate the fault and stop reporting
> + * page faults if possible.
The comment refers to function and values that haven't been defined yet.
Either the page_response() patch should come before, or we need to split
this patch.
Something I missed before: if the handler fails (returns != 0) it should
complete the fault by calling iommu_page_response(), if we're not doing
it in iommu_report_device_fault(). It should be indicated in this
comment. It's safe for the handler to call page_response() since we're
not holding fault_param->lock when calling the handler.
> + *
> + * Return 0 if the fault handler was installed successfully, or an error.
> + */
[...]
> +/**
> + * 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)
> +{
> + int ret = 0;
> + struct iommu_fault_event *evt_pending;
> + struct iommu_fault_param *fparam;
> +
> + /* iommu_param is allocated when device is added to group */
> + if (!dev->iommu_param | !evt)
Typo: ||
Thanks,
Jean
> + return -EINVAL;
> + /* we only report device fault if there is a handler registered */
> + mutex_lock(>iommu_param->lock);
> + if (!dev->iommu_param->fault_param ||
> + !dev->iommu_param->fault_param->handler) {
> + ret = -EINVAL;
> + goto done_unlock;
> + }
> + fparam = dev->iommu_param->fault_param;
> + if (evt->fault.type == IOMMU_FAULT_PAGE_REQ &&
> + evt->fault.prm.flags & IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE) {
> + evt_pending = kmemdup(evt, sizeof(struct iommu_fault_event),
> + GFP_KERNEL);
> + if (!evt_pending) {
> + ret = -ENOMEM;
> + goto done_unlock;
> + }
> + mutex_lock(>lock);
> + list_add_tail(_pending->list, >faults);
> + mutex_unlock(>lock);
> + }
> + ret = fparam->handler(evt, fparam->data);
> +done_unlock:
> + mutex_unlock(>iommu_param->lock);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_report_device_fault);
[...]
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[PATCH v4 03/22] iommu: introduce device fault report API
From: 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.
Faults detected by IOMMU is based on the transaction's source ID which
can be reported at per device basis, regardless of the device type is a
PCI device or not.
The fault types include recoverable (e.g. page request) and
unrecoverable faults(e.g. access error). In most cases, faults can be
handled by IOMMU drivers internally. The primary use cases are as
follows:
1. page request fault originated from an SVM capable device that is
assigned to guest via vIOMMU. In this case, the first level page tables
are owned by the guest. Page request must be propagated to the guest to
let guest OS fault in the pages then send page response. In this
mechanism, the direct receiver of IOMMU fault notification is VFIO,
which can relay notification events to QEMU or other user space
software.
2. faults need more subtle handling by device drivers. Other than
simply invoke reset function, there are needs to let device driver
handle the fault with a smaller impact.
This patchset is intended to create a generic fault report API such
that it can scale as follows:
- all IOMMU types
- PCI and non-PCI devices
- recoverable and unrecoverable faults
- VFIO and other other in kernel users
- DMA & IRQ remapping (TBD)
The original idea was brought up by David Woodhouse and discussions
summarized at https://lwn.net/Articles/608914/.
Signed-off-by: Jacob Pan
Signed-off-by: Ashok Raj
Signed-off-by: Jean-Philippe Brucker
Signed-off-by: Eric Auger
[adapt to new iommu_fault fault field, test fault_param on
iommu_unregister_device_fault_handler]
---
drivers/iommu/iommu.c | 154 +-
include/linux/iommu.h | 36 +-
2 files changed, 188 insertions(+), 2 deletions(-)
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 3ed4db334341..c297cdcf7f89 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(>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(>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(>kobj, "iommu_group");
trace_remove_device_from_group(group->id, dev);
-
+ kfree(dev->iommu_param);
kfree(device->name);
kfree(device);
dev->iommu_group = NULL;
@@ -858,6 +866,150 @@ 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, call this handler with the fault
event
+ * and data as argument. The handler should return 0 on success. If the fault
is
+ * recoverable (IOMMU_FAULT_PAGE_REQ), the handler can also complete
+ * the fault by calling iommu_page_response() with one of the following
+ * response code:
+ * - IOMMU_PAGE_RESP_SUCCESS: retry the translation
+ * - IOMMU_PAGE_RESP_INVALID: terminate the fault
+ * - IOMMU_PAGE_RESP_FAILURE: terminate the fault and stop reporting
+ * page faults if possible.
+ *
+ * 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(>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);
+
