[PULL for-11.1 3/3] s390x/css: firm up handling of chained TIC CCWs

[Cornelia Huck <cohuck@redhat.com>]

From: Eric Farman <farman@linux.ibm.com>

The logic in css_interpret_ccw() correctly returns -EINVAL if a
Transfer-In-Channel (TIC) CCW is command chained to another TIC CCW.
The same routine also correctly returns -EINVAL if 256 CCWs do not
perform a data transfer as part of the I/O operation [0].

What is missing, however, is a combination of these two, where a loop
can be generated that will continue processing CCWs but without
providing an opportunity to catch a breath. Fix this by capping
the number of TIC CCWs in a channel program at the same limit as
the CCWs without data transfer.

[0] See "Invalid Sequence" in z/Architecture Principles of Operation
    (SA22-7832-14), p16-27

Cc: qemu-stable@nongnu.org
Signed-off-by: Eric Farman <farman@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Message-ID: <20260713074708.884282-1-borntraeger@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---
 hw/s390x/css.c         | 7 +++++++
 include/hw/s390x/css.h | 1 +
 2 files changed, 8 insertions(+)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 29ba39f79ea1..3a67b6705319 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -1078,6 +1078,12 @@ static int css_interpret_ccw(SubchDev *sch, hwaddr ccw_addr,
             ret = -EINVAL;
             break;
         }
+        /* Limit the number of TICs in a given channel program */
+        if (sch->ccw_tic_cnt == 255) {
+            ret = -EINVAL;
+            break;
+        }
+        sch->ccw_tic_cnt++;
         sch->channel_prog = ccw.cda;
         ret = -EAGAIN;
         break;
@@ -1129,6 +1135,7 @@ static void sch_handle_start_func_virtual(SubchDev *sch)
         sch->ccw_fmt_1 = !!(orb->ctrl0 & ORB_CTRL0_MASK_FMT);
         schib->scsw.flags |= (sch->ccw_fmt_1) ? SCSW_FLAGS_MASK_FMT : 0;
         sch->ccw_no_data_cnt = 0;
+        sch->ccw_tic_cnt = 0;
         suspend_allowed = !!(orb->ctrl0 & ORB_CTRL0_MASK_SPND);
     } else {
         /* Start Function resumed via rsch */
diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
index d3326237c9f0..79b41f305e8c 100644
--- a/include/hw/s390x/css.h
+++ b/include/hw/s390x/css.h
@@ -132,6 +132,7 @@ struct SubchDev {
     bool ccw_fmt_1;
     bool thinint_active;
     uint8_t ccw_no_data_cnt;
+    uint8_t ccw_tic_cnt;
     uint16_t migrated_schid; /* used for mismatch detection */
     CcwDataStream cds;
     /* transport-provided data: */
-- 
2.55.0