Re: [PATCH v3 10/16] iommu: introduce device fault report API

[Lu Baolu]

Hi,

On 11/18/2017 02:55 AM, 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.
>
> 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 <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> ---
>  drivers/iommu/iommu.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/iommu.h | 36 +++++++++++++++++++++++++++++
>  2 files changed, 98 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 829e9e9..97b7990 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -581,6 +581,12 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
>  		goto err_free_name;
>  	}
>  
> +	dev->iommu_param = kzalloc(sizeof(struct iommu_fault_param), GFP_KERNEL);
> +	if (!dev->iommu_param) {
> +		ret = -ENOMEM;
> +		goto err_free_name;
> +	}
> +
>  	kobject_get(group->devices_kobj);
>  
>  	dev->iommu_group = group;
> @@ -657,7 +663,7 @@ 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;
> @@ -791,6 +797,61 @@ int iommu_group_unregister_notifier(struct iommu_group *group,
>  }
>  EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier);
>  
> +int iommu_register_device_fault_handler(struct device *dev,
> +					iommu_dev_fault_handler_t handler,
> +					void *data)
> +{
> +	struct iommu_param *idata = dev->iommu_param;
> +
> +	/*
> +	 * Device iommu_param should have been allocated when device is
> +	 * added to its iommu_group.
> +	 */
> +	if (!idata)
> +		return -EINVAL;
> +	/* Only allow one fault handler registered for each device */
> +	if (idata->fault_param)
> +		return -EBUSY;
> +	get_device(dev);
> +	idata->fault_param =
> +		kzalloc(sizeof(struct iommu_fault_param), GFP_KERNEL);
> +	if (!idata->fault_param)
> +		return -ENOMEM;
> +	idata->fault_param->handler = handler;
> +	idata->fault_param->data = data;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(iommu_register_device_fault_handler);
> +
> +int iommu_unregister_device_fault_handler(struct device *dev)
> +{
> +	struct iommu_param *idata = dev->iommu_param;
> +
> +	if (!idata)
> +		return -EINVAL;
> +
> +	kfree(idata->fault_param);
> +	idata->fault_param = NULL;
> +	put_device(dev);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(iommu_unregister_device_fault_handler);
> +
> +
> +int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
> +{
> +	/* we only report device fault if there is a handler registered */
> +	if (!dev->iommu_param || !dev->iommu_param->fault_param ||
> +		!dev->iommu_param->fault_param->handler)

Can this replaced by:

    if (!iommu_has_device_fault_handler(dev))

?

Best regards,
Lu Baolu

> +		return -ENOSYS;
> +
> +	return dev->iommu_param->fault_param->handler(evt,
> +						dev->iommu_param->fault_param->data);
> +}
> +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 dfda89b..841c044 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -463,6 +463,14 @@ 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 *);
> @@ -481,6 +489,12 @@ extern void iommu_domain_window_disable(struct iommu_domain *domain, u32 wnd_nr)
>  extern int report_iommu_fault(struct iommu_domain *domain, struct device *dev,
>  			      unsigned long iova, int flags);
>  
> +static inline bool iommu_has_device_fault_handler(struct device *dev)
> +{
> +	return dev->iommu_param && dev->iommu_param->fault_param &&
> +		dev->iommu_param->fault_param->handler;
> +}
> +
>  static inline void iommu_flush_tlb_all(struct iommu_domain *domain)
>  {
>  	if (domain->ops->flush_iotlb_all)
> @@ -734,6 +748,28 @@ 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 0;
> +}
> +
> +static inline int iommu_unregister_device_fault_handler(struct device *dev)
> +{
> +	return 0;
> +}
> +
> +static inline bool iommu_has_device_fault_handler(struct device *dev)
> +{
> +	return false;
> +}
> +
> +static inline int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
> +{
> +	return 0;
> +}
> +
>  static inline int iommu_group_id(struct iommu_group *group)
>  {
>  	return -ENODEV;