iommu/vt-d: Don't set then clear private data in prq_event_thread()

The VT-d specification (section 7.6) requires that the value in the Private Data field of a Page Group Response Descriptor must match the value in the Private Data field of the respective Page Request Descriptor.

The private data field of a page group response descriptor is set then immediately cleared in prq_event_thread(). This breaks the rule defined by the VT-d specification. Fix it by moving clearing code up.

---
 drivers/iommu/intel/svm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Log:
v1->v2:
- v1: https://lore.kernel.org/linux-iommu/[email protected]/
- Refine the commit title to make the affected field clear.
- Refine the commit message to declare why the change matters.

index 677d7f6b43bb..5d590d63ab52 100644
@@ -1034,12 +1034,12 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 				QI_PGRP_RESP_TYPE;
 			resp.qw1 = QI_PGRP_IDX(req->prg_index) |
 				QI_PGRP_LPIG(req->lpig);
+			resp.qw2 = 0;
+			resp.qw3 = 0;
 
 			if (req->priv_data_present)
 				memcpy(&resp.qw2, req->priv_data,
 				       sizeof(req->priv_data));
-			resp.qw2 = 0;
-			resp.qw3 = 0;
 			qi_submit_sync(iommu, &resp, 1, 0);
 		}
 prq_advance:

2.25.1

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Applied, thanks.