[PATCH v1 11/16] vfio/ccw: discard second fmt-1 IDAW

[Eric Farman <farman@linux.ibm.com>]

The intention is to read the first IDAW to determine the starting
location of an I/O operation, knowing that the second and any/all
subsequent IDAWs will be aligned per architecture. But, this read
receives 64-bits of data, which is the size of a format-2 IDAW.

In the event that Format-1 IDAWs are presented, discard the lower
32 bits as they contain the second IDAW in such a list.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 drivers/s390/cio/vfio_ccw_cp.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index 34a133d962d1..53246f4f95f7 100644
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/drivers/s390/cio/vfio_ccw_cp.c
@@ -516,11 +516,15 @@ static int ccw_count_idaws(struct ccw1 *ccw,
 		bytes = ccw->count;
 
 	if (ccw_is_idal(ccw)) {
-		/* Read first IDAW to see if it's 4K-aligned or not. */
-		/* All subsequent IDAws will be 4K-aligned. */
+		/* Read first IDAW to check its starting address. */
+		/* All subsequent IDAWs will be 2K- or 4K-aligned. */
 		ret = vfio_dma_rw(vdev, ccw->cda, &iova, sizeof(iova), false);
 		if (ret)
 			return ret;
+
+		/* Format-1 IDAWs only occupy the first int */
+		if (!cp->orb.cmd.c64)
+			iova = iova >> 32;
 	} else {
 		iova = ccw->cda;
 	}
-- 
2.34.1