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Subject[PATCH v2 4/4] iommu: Add recoverable fault reporting
Date
Some IOMMU hardware features, for example PCI PRI and Arm SMMU Stall,
enable recoverable I/O page faults. Allow IOMMU drivers to report PRI Page
Requests and Stall events through the new fault reporting API. The
consumer of the fault can be either an I/O page fault handler in the host,
or a guest OS.

Once handled, the fault must be completed by sending a page response back
to the IOMMU. Add an iommu_page_response() function to complete a page
fault.

There are two ways to extend the userspace API:
* Add a field to iommu_page_response and a flag to
iommu_page_response::flags describing the validity of this field.
* Introduce a new iommu_page_response_X structure with a different version
number. The kernel must then support both versions.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
---
drivers/iommu/iommu.c | 94 +++++++++++++++++++++++++++++++++++++-
include/linux/iommu.h | 19 ++++++++
include/uapi/linux/iommu.h | 35 ++++++++++++++
3 files changed, 146 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 8037a3f07f07..956a80364efd 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -891,7 +891,14 @@ EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier);
* @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. The handler should return 0 on success.
+ * fault event and data as argument. The handler should return 0 on success. If
+ * the fault is recoverable (IOMMU_FAULT_PAGE_REQ), the consumer should 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.
*/
@@ -921,6 +928,8 @@ int iommu_register_device_fault_handler(struct device *dev,
}
param->fault_param->handler = handler;
param->fault_param->data = data;
+ mutex_init(&param->fault_param->lock);
+ INIT_LIST_HEAD(&param->fault_param->faults);

done_unlock:
mutex_unlock(&param->lock);
@@ -951,6 +960,12 @@ int iommu_unregister_device_fault_handler(struct device *dev)
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);
@@ -967,13 +982,15 @@ EXPORT_SYMBOL_GPL(iommu_unregister_device_fault_handler);
* @evt: fault event data
*
* Called by IOMMU drivers when a fault is detected, typically in a threaded IRQ
- * handler.
+ * handler. When this function fails and the fault is recoverable, it is the
+ * caller's responsibility to complete the fault.
*
* 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_event *evt_pending = NULL;
struct iommu_fault_param *fparam;
int ret = 0;

@@ -987,13 +1004,86 @@ int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
ret = -EINVAL;
goto done_unlock;
}
+
+ 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(&fparam->lock);
+ list_add_tail(&evt_pending->list, &fparam->faults);
+ mutex_unlock(&fparam->lock);
+ }
+
ret = fparam->handler(&evt->fault, fparam->data);
+ if (ret && evt_pending) {
+ mutex_lock(&fparam->lock);
+ list_del(&evt_pending->list);
+ mutex_unlock(&fparam->lock);
+ kfree(evt_pending);
+ }
done_unlock:
mutex_unlock(&param->lock);
return ret;
}
EXPORT_SYMBOL_GPL(iommu_report_device_fault);

+int iommu_page_response(struct device *dev,
+ struct iommu_page_response *msg)
+{
+ bool pasid_valid;
+ int ret = -EINVAL;
+ struct iommu_fault_event *evt;
+ struct iommu_fault_page_request *prm;
+ struct iommu_param *param = dev->iommu_param;
+ struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
+
+ if (!domain || !domain->ops->page_response)
+ return -ENODEV;
+
+ if (!param || !param->fault_param)
+ return -EINVAL;
+
+ if (msg->version != IOMMU_PAGE_RESP_VERSION_1 ||
+ msg->flags & ~IOMMU_PAGE_RESP_PASID_VALID)
+ return -EINVAL;
+
+ /* Only send response if there is a fault report pending */
+ mutex_lock(&param->fault_param->lock);
+ if (list_empty(&param->fault_param->faults)) {
+ dev_warn_ratelimited(dev, "no pending PRQ, drop response\n");
+ goto done_unlock;
+ }
+ /*
+ * Check if we have a matching page request pending to respond,
+ * otherwise return -EINVAL
+ */
+ list_for_each_entry(evt, &param->fault_param->faults, list) {
+ prm = &evt->fault.prm;
+ pasid_valid = prm->flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID;
+
+ if ((pasid_valid && prm->pasid != msg->pasid) ||
+ prm->grpid != msg->grpid)
+ continue;
+
+ /* Sanitize the reply */
+ msg->flags = pasid_valid ? IOMMU_PAGE_RESP_PASID_VALID : 0;
+
+ ret = domain->ops->page_response(dev, evt, msg);
+ list_del(&evt->list);
+ kfree(evt);
+ break;
+ }
+
+done_unlock:
+ mutex_unlock(&param->fault_param->lock);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(iommu_page_response);
+
/**
* 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 3e783f5bf472..76c8cda61dfd 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -227,6 +227,7 @@ struct iommu_sva_ops {
* @sva_bind: Bind process address space to device
* @sva_unbind: Unbind process address space from device
* @sva_get_pasid: Get PASID associated to a SVA handle
+ * @page_response: handle page request response
* @pgsize_bitmap: bitmap of all possible supported page sizes
*/
struct iommu_ops {
@@ -287,6 +288,10 @@ struct iommu_ops {
void (*sva_unbind)(struct iommu_sva *handle);
int (*sva_get_pasid)(struct iommu_sva *handle);

+ int (*page_response)(struct device *dev,
+ struct iommu_fault_event *evt,
+ struct iommu_page_response *msg);
+
unsigned long pgsize_bitmap;
};

@@ -311,19 +316,25 @@ struct iommu_device {
* unrecoverable faults such as DMA or IRQ remapping faults.
*
* @fault: fault descriptor
+ * @list: pending fault event list, used for tracking responses
*/
struct iommu_fault_event {
struct iommu_fault fault;
+ struct list_head list;
};

/**
* struct iommu_fault_param - per-device IOMMU fault data
* @handler: Callback function to handle IOMMU faults at device level
* @data: handler private data
+ * @faults: holds the pending faults which needs response
+ * @lock: protect pending faults list
*/
struct iommu_fault_param {
iommu_dev_fault_handler_t handler;
void *data;
+ struct list_head faults;
+ struct mutex lock;
};

/**
@@ -437,6 +448,8 @@ 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_page_response(struct device *dev,
+ struct iommu_page_response *msg);

extern int iommu_group_id(struct iommu_group *group);
extern struct iommu_group *iommu_group_get_for_dev(struct device *dev);
@@ -765,6 +778,12 @@ int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
return -ENODEV;
}

+static inline int iommu_page_response(struct device *dev,
+ struct iommu_page_response *msg)
+{
+ return -ENODEV;
+}
+
static inline int iommu_group_id(struct iommu_group *group)
{
return -ENODEV;
diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
index 796402174d6c..f45d8e9e59c3 100644
--- a/include/uapi/linux/iommu.h
+++ b/include/uapi/linux/iommu.h
@@ -115,4 +115,39 @@ struct iommu_fault {
struct iommu_fault_page_request prm;
};
};
+
+/**
+ * enum iommu_page_response_code - Return status of fault handlers
+ * @IOMMU_PAGE_RESP_SUCCESS: Fault has been handled and the page tables
+ * populated, retry the access. This is "Success" in PCI PRI.
+ * @IOMMU_PAGE_RESP_FAILURE: General error. Drop all subsequent faults from
+ * this device if possible. This is "Response Failure" in PCI PRI.
+ * @IOMMU_PAGE_RESP_INVALID: Could not handle this fault, don't retry the
+ * access. This is "Invalid Request" in PCI PRI.
+ */
+enum iommu_page_response_code {
+ IOMMU_PAGE_RESP_SUCCESS = 0,
+ IOMMU_PAGE_RESP_INVALID,
+ IOMMU_PAGE_RESP_FAILURE,
+};
+
+/**
+ * struct iommu_page_response - Generic page response information
+ * @version: API version of this structure
+ * @flags: encodes whether the corresponding fields are valid
+ * (IOMMU_FAULT_PAGE_RESPONSE_* values)
+ * @pasid: Process Address Space ID
+ * @grpid: Page Request Group Index
+ * @code: response code from &enum iommu_page_response_code
+ */
+struct iommu_page_response {
+#define IOMMU_PAGE_RESP_VERSION_1 1
+ __u32 version;
+#define IOMMU_PAGE_RESP_PASID_VALID (1 << 0)
+ __u32 flags;
+ __u32 pasid;
+ __u32 grpid;
+ __u32 code;
+};
+
#endif /* _UAPI_IOMMU_H */
--
2.21.0
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