[PATCH v2 1/1] iommu/vt-d: Don't set then clear private data in prq_event_thread()

[Lu Baolu]

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.

Fixes: 5b438f4ba315d ("iommu/vt-d: Support page request in scalable mode")
Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
Reviewed-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/iommu/intel/svm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Log:
v1->v2:
  - v1: https://lore.kernel.org/linux-iommu/20210309004641.3809653-1-baolu.lu@xxxxxxxxxxxxxxx/
  - Refine the commit title to make the affected field clear.
  - Refine the commit message to declare why the change matters.

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 677d7f6b43bb..5d590d63ab52 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -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