s390x/css: handle emw correctly for tsch

We should not try to store the emw portion of the irb if extended
measurements are not applicable. In particular, we should not surprise
the guest by storing a larger irb if it did not enable extended
measurements.

Cc: qemu-stable@nongnu.org
Reviewed-by: NDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Tested-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

hw/s390x/css.c

@@ -779,9 +779,11 @@ out:
     return ret;
 }
 
-static void copy_irb_to_guest(IRB *dest, const IRB *src)
+static void copy_irb_to_guest(IRB *dest, const IRB *src, PMCW *pmcw)
 {
     int i;
+    uint16_t stctl = src->scsw.ctrl & SCSW_CTRL_MASK_STCTL;
+    uint16_t actl = src->scsw.ctrl & SCSW_CTRL_MASK_ACTL;
 
     copy_scsw_to_guest(&dest->scsw, &src->scsw);
 
@@ -791,8 +793,22 @@ static void copy_irb_to_guest(IRB *dest, const IRB *src)
     for (i = 0; i < ARRAY_SIZE(dest->ecw); i++) {
         dest->ecw[i] = cpu_to_be32(src->ecw[i]);
     }
-    for (i = 0; i < ARRAY_SIZE(dest->emw); i++) {
-        dest->emw[i] = cpu_to_be32(src->emw[i]);
+    /* extended measurements enabled? */
+    if ((src->scsw.flags & SCSW_FLAGS_MASK_ESWF) ||
+        !(pmcw->flags & PMCW_FLAGS_MASK_TF) ||
+        !(pmcw->chars & PMCW_CHARS_MASK_XMWME)) {
+        return;
+    }
+    /* extended measurements pending? */
+    if (!(stctl & SCSW_STCTL_STATUS_PEND)) {
+        return;
+    }
+    if ((stctl & SCSW_STCTL_PRIMARY) ||
+        (stctl == SCSW_STCTL_SECONDARY) ||
+        ((stctl & SCSW_STCTL_INTERMEDIATE) && (actl & SCSW_ACTL_SUSP))) {
+        for (i = 0; i < ARRAY_SIZE(dest->emw); i++) {
+            dest->emw[i] = cpu_to_be32(src->emw[i]);
+        }
     }
 }
 
@@ -838,7 +854,7 @@ int css_do_tsch(SubchDev *sch, IRB *target_irb)
         }
     }
     /* Store the irb to the guest. */
-    copy_irb_to_guest(target_irb, &irb);
+    copy_irb_to_guest(target_irb, &irb, p);
 
     /* Clear conditions on subchannel, if applicable. */
     if (stctl & SCSW_STCTL_STATUS_PEND) {