[PATCH 1/1] vfio-ccw: Keep passthrough sense data intact

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

For virtual devices, there is space for sense data to be built
and later copied into the IRB's ECW space once a TSCH is handled.

For passthrough devices, the IRB is passed up from hardware.
There might already be sense data in the ECW, in which case it
would be unusual to overwrite the IRB ESW/ECW data with itself.

In either case, if there isn't sense data, then an explicit SENSE
operation might be needed from the guest driver. Regardless,
fabricating sense data out of zeros seems like it would result
in unexpected behavior.

Let's remove the copying of the ECW/sense data in the vfio-ccw
driver, and adapt the check in the TSCH handler to look for
non-zero data in the local sense data before building a sense
data response in the IRB.

This fixes a "dasdfmt -M quick" command issued within a guest.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 hw/s390x/css.c | 3 ++-
 hw/vfio/ccw.c  | 6 ------
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index bed46f5ec3..29234daa27 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -1661,7 +1661,8 @@ int css_do_tsch_get_irb(SubchDev *sch, IRB *target_irb, int *irb_len)
         }
         /* If a unit check is pending, copy sense data. */
         if ((schib->scsw.dstat & SCSW_DSTAT_UNIT_CHECK) &&
-            (schib->pmcw.chars & PMCW_CHARS_MASK_CSENSE)) {
+            (schib->pmcw.chars & PMCW_CHARS_MASK_CSENSE) &&
+            (sch->sense_data[0] != 0)) {
             int i;
 
             irb.scsw.flags |= SCSW_FLAGS_MASK_ESWF | SCSW_FLAGS_MASK_ECTL;
diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
index 139a3d9d1b..a4dc4acb34 100644
--- a/hw/vfio/ccw.c
+++ b/hw/vfio/ccw.c
@@ -371,12 +371,6 @@ static void vfio_ccw_io_notifier_handler(void *opaque)
     copy_scsw_to_guest(&s, &irb.scsw);
     schib->scsw = s;
 
-    /* If a uint check is pending, copy sense data. */
-    if ((schib->scsw.dstat & SCSW_DSTAT_UNIT_CHECK) &&
-        (schib->pmcw.chars & PMCW_CHARS_MASK_CSENSE)) {
-        memcpy(sch->sense_data, irb.ecw, sizeof(irb.ecw));
-    }
-
 read_err:
     css_inject_io_interrupt(sch);
 }
-- 
2.25.1