spapr/xive: skip partially initialized vCPUs in presenter

When vCPUs are hotplugged, they are added to the QEMU CPU list before
being fully realized. This can crash the XIVE presenter because the
'tctx' pointer is not necessarily initialized when looking for a
matching target.

These vCPUs are not valid targets for the presenter. Skip them.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20191001085722.32755-1-clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>

hw/intc/xive.c

@@ -1396,6 +1396,14 @@ static bool xive_presenter_match(XiveRouter *xrtr, uint8_t format,
         XiveTCTX *tctx = xive_router_get_tctx(xrtr, cs);
         int ring;
 
+        /*
+         * Skip partially initialized vCPUs. This can happen when
+         * vCPUs are hotplugged.
+         */
+        if (!tctx) {
+            continue;
+        }
+
         /*
          * HW checks that the CPU is enabled in the Physical Thread
          * Enable Register (PTER).