[Qemu-devel] [PATCH 1/4] s390x/css: drop data-check in interpretation

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

The architecture says that channel-data check is indicating that
an uncorrected storage (memory) error has been detected in regard
to the data residing in main storage (memory) that is currently
used for an I/O operation. The described detection is done using
the CBC technology.

The ccw interpretation code is however generating a channel-data check
effectively when the (device specific) ccw_cb returns -EFAULT.  In case
of virtio-ccw devices this happens when mapping memory fails, or when a
NULL pointer is encountered. So this behavior is not architecture
conform.

Furthermore the best fit for these situations (null pointer, mapping a
piece of guest memory fails) from architectural perspective the condition
described as the channel subsystem refers to a location that is not
available, which when encountered shall result in a channel-program
check.

To fix this, all we have to do is to get rid of the switch case matching
-EFAULT: the default is generating a channel-program check.

---

Was posted as stand alone patch. See:
http://patchwork.ozlabs.org/patch/810995/

If you are going to, *please review there*.

Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
---
 hw/s390x/css.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 901dc6a0f3..09f6ba0310 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -980,15 +980,6 @@ static void sch_handle_start_func_virtual(SubchDev *sch)
                     SCSW_STCTL_ALERT | SCSW_STCTL_STATUS_PEND;
             s->cpa = sch->channel_prog + 8;
             break;
-        case -EFAULT:
-            /* memory problem, generate channel data check */
-            s->ctrl &= ~SCSW_ACTL_START_PEND;
-            s->cstat = SCSW_CSTAT_DATA_CHECK;
-            s->ctrl &= ~SCSW_CTRL_MASK_STCTL;
-            s->ctrl |= SCSW_STCTL_PRIMARY | SCSW_STCTL_SECONDARY |
-                    SCSW_STCTL_ALERT | SCSW_STCTL_STATUS_PEND;
-            s->cpa = sch->channel_prog + 8;
-            break;
         case -EBUSY:
             /* subchannel busy, generate deferred cc 1 */
             s->flags &= ~SCSW_FLAGS_MASK_CC;
-- 
2.13.5