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SubjectRE: [PATCH v5 13/23] iommu: introduce device fault report API
Date
> From: Jacob Pan [mailto:jacob.jun.pan@linux.intel.com]
> Sent: Saturday, May 12, 2018 4:54 AM
>
> 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@linux.intel.com>
> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> ---
> drivers/iommu/iommu.c | 149
> +++++++++++++++++++++++++++++++++++++++++++++++++-
> include/linux/iommu.h | 35 +++++++++++-
> 2 files changed, 181 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index
> 3a49b96..b3f9daf 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -609,6 +609,13 @@ 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;
> @@ -639,6 +646,7 @@ 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:
> @@ -685,7 +693,7 @@ 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;
> @@ -820,6 +828,145 @@ 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(&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);
> + /* 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) {
> + 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)
> + return -EINVAL;
> + /* we only report device fault if there is a handler registered */
> + mutex_lock(&dev->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->type == IOMMU_FAULT_PAGE_REQ && evt->last_req) {
> + evt_pending = kmemdup(evt, sizeof(struct iommu_fault_event),
> + GFP_KERNEL);
> + if (!evt_pending) {
> + ret = -ENOMEM;
> + goto done_unlock;
> + }
> + mutex_lock(&fparam->lock);
> + list_add_tail(&evt_pending->list, &fparam->faults);

I may missed it. Here only see list add, how about removing? Who would remove
entry from the fault list?

> + mutex_unlock(&fparam->lock);
> + }
> + ret = fparam->handler(evt, fparam->data);

I remember you mentioned there will be a queue to store the faults. Is it in the
fparam->faults list? Or there is no such queue?

Thanks,
Yi Liu

> +done_unlock:
> + mutex_unlock(&dev->iommu_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 aeadb4f..b3312ee
> 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -307,7 +307,8 @@ enum iommu_fault_reason {
> * and PASID spec.
> * - Un-recoverable faults of device interest
> * - DMA remapping and IRQ remapping faults
> -
> + *
> + * @list pending fault event list, used for tracking responses
> * @type contains fault type.
> * @reason fault reasons if relevant outside IOMMU driver, IOMMU driver internal
> * faults are not reported
> @@ -324,6 +325,7 @@ enum iommu_fault_reason {
> * sending the fault response.
> */
> struct iommu_fault_event {
> + struct list_head list;
> enum iommu_fault_type type;
> enum iommu_fault_reason reason;
> u64 addr;
> @@ -340,10 +342,13 @@ 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;
> };
>
> @@ -357,6 +362,7 @@ struct iommu_fault_param {
> * struct iommu_fwspec *iommu_fwspec;
> */
> struct iommu_param {
> + struct mutex lock;
> struct iommu_fault_param *fault_param; };
>
> @@ -456,6 +462,14 @@ 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 *); @@ -
> 727,6 +741,23 @@ 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

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