[RFC PATCHES 02/17] iommu: Support asynchronous I/O page fault response

[Lu Baolu <baolu.lu@linux.intel.com>]

Add a new page response code, IOMMU_PAGE_RESP_ASYNC, to indicate that the
domain's page fault handler doesn't respond the hardware immediately, but
do it in an asynchronous way.

The use case of this response code is the nested translation, where the
first-stage page table is owned by the VM guest and any page fault on
it should be propagated to the VM guest and page fault will be responded
in a different thread context later.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 include/linux/iommu.h      | 2 ++
 drivers/iommu/io-pgfault.c | 3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index d6a93de7d1dd..fce7ad81206f 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -164,11 +164,13 @@ struct iommu_fault {
  *	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.
+ * @IOMMU_PAGE_RESP_ASYNC: Will response later by calling iommu_page_response().
  */
 enum iommu_page_response_code {
 	IOMMU_PAGE_RESP_SUCCESS = 0,
 	IOMMU_PAGE_RESP_INVALID,
 	IOMMU_PAGE_RESP_FAILURE,
+	IOMMU_PAGE_RESP_ASYNC,
 };
 
 /**
diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
index e5b8b9110c13..83f8055a0e09 100644
--- a/drivers/iommu/io-pgfault.c
+++ b/drivers/iommu/io-pgfault.c
@@ -96,7 +96,8 @@ static void iopf_handler(struct work_struct *work)
 			kfree(iopf);
 	}
 
-	iopf_complete_group(group->dev, &group->last_fault, status);
+	if (status != IOMMU_PAGE_RESP_ASYNC)
+		iopf_complete_group(group->dev, &group->last_fault, status);
 	kfree(group);
 }
 
-- 
2.34.1