[qemu-s390x] [PATCH] s390x/css: disabled subchannels cannot be status pending

[Cornelia Huck]

The 3270 code will try to post an attention interrupt when the
3270 emulator (e.g. x3270) attaches. If the guest has not yet
enabled the subchannel for the 3270 device, we will give it a
spurious status during msch when it does so later.

To fix this, just don't do anything in css_conditional_io_interrupt()
if the subchannel is not enabled. The 3270 code will work fine with
that, and the other user of this function (virtio-ccw) never
attempts to post an interrupt for a disabled device to begin with.

Reported-by: Thomas Huth <address@hidden>
Signed-off-by: Cornelia Huck <address@hidden>
---
 hw/s390x/css.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 301bf1772f..56c3fa8c89 100644
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -616,6 +616,14 @@ void css_inject_io_interrupt(SubchDev *sch)
 
 void css_conditional_io_interrupt(SubchDev *sch)
 {
+    /*
+     * If the subchannel is not enabled, it is not made status pending
+     * (see PoP p. 16-17, "Status Control").
+     */
+    if (!(sch->curr_status.pmcw.flags & PMCW_FLAGS_MASK_ENA)) {
+        return;
+    }
+
     /*
      * If the subchannel is not currently status pending, make it pending
      * with alert status.
-- 
2.14.3