[Qemu-devel] [PATCH 2/9] s390x: fix invalid use of cc 1 for SSCH

[Halil Pasic <pasic@linux.vnet.ibm.com>]

According to the POP a start subchannel instruction (SSCH) returning with
cc 1 implies that the subchannel was status pending when SSCH executed.

Due to a somewhat confusing error handling, where error codes are mapped
to cc value, sane looking error codes result in non AR compliant
behavior.

Let's fix this! Instead of cc 1 we use cc 3 which means device not
operational, and is much closer to the truth in the given cases.

Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Acked-by: Pierre Morel<pmorel@linux.vnet.ibm.com>
---

This patch turned out quite controversial. We did not reach a consensus
during the internal review.

The most of the discussion revolved around the ORB flag which
architecturally must be supported, but are currently not supported by
vfio-ccw (not yet, or can't be). The idea showing the most promise for
consensus was to handle this via device status (along the lines better a
strange acting device than a non-conform machine) but since it's a
radical change we decided to first discuss upstream and then do whatever
needs to be done.
---
 hw/s390x/css.c      | 15 ++++++---------
 hw/s390x/s390-ccw.c |  2 +-
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index a50fb0727e..0822538cde 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -1034,7 +1034,7 @@ static int sch_handle_start_func_passthrough(SubchDev *sch)
      */
     if (!(orb->ctrl0 & ORB_CTRL0_MASK_PFCH) ||
         !(orb->ctrl0 & ORB_CTRL0_MASK_C64)) {
-        return -EINVAL;
+        return -ENODEV;
     }
 
     ret = s390_ccw_cmd_request(orb, s, sch->driver_data);
@@ -1046,16 +1046,13 @@ static int sch_handle_start_func_passthrough(SubchDev *sch)
         break;
     case -ENODEV:
         break;
+    case -EFAULT:
+         break;
     case -EACCES:
         /* Let's reflect an inaccessible host device by cc 3. */
-        ret = -ENODEV;
-        break;
     default:
-       /*
-        * All other return codes will trigger a program check,
-        * or set cc to 1.
-        */
-       break;
+        /* Let's make all other return codes map to cc 3.  */
+        ret = -ENODEV;
     };
 
     return ret;
@@ -1115,7 +1112,7 @@ static int do_subchannel_work(SubchDev *sch)
     if (sch->do_subchannel_work) {
         return sch->do_subchannel_work(sch);
     } else {
-        return -EINVAL;
+        return -ENODEV;
     }
 }
 
diff --git a/hw/s390x/s390-ccw.c b/hw/s390x/s390-ccw.c
index 8614dda6f8..2b0741741c 100644
--- a/hw/s390x/s390-ccw.c
+++ b/hw/s390x/s390-ccw.c
@@ -25,7 +25,7 @@ int s390_ccw_cmd_request(ORB *orb, SCSW *scsw, void *data)
     if (cdc->handle_request) {
         return cdc->handle_request(orb, scsw, data);
     } else {
-        return -ENOSYS;
+        return -ENODEV;
     }
 }
 
-- 
2.13.5