hw/intc/arm_gicv3_its: In MAPC with V=0, don't check rdbase field

In the MAPC command, if V=0 this is a request to delete a collection
table entry and the rdbase field of the command packet will not be
used.  In particular, the specification says that the "UNPREDICTABLE
if rdbase is not valid" only applies for V=1.

We were doing a check-and-log-guest-error on rdbase regardless of
whether the V bit was set, and also (harmlessly but confusingly)
storing the contents of the rdbase field into the updated collection
table entry.  Update the code so that if V=0 we don't check or use
the rdbase field value.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220201193207.2771604-12-peter.maydell@linaro.org

hw/intc/arm_gicv3_its.c

@@ -468,21 +468,21 @@ static ItsCmdResult process_mapc(GICv3ITSState *s, const uint64_t *cmdpkt)
     CTEntry cte;
 
     icid = cmdpkt[2] & ICID_MASK;
-
-    cte.rdbase = (cmdpkt[2] & R_MAPC_RDBASE_MASK) >> R_MAPC_RDBASE_SHIFT;
-    cte.rdbase &= RDBASE_PROCNUM_MASK;
-
     cte.valid = cmdpkt[2] & CMD_FIELD_VALID_MASK;
+    if (cte.valid) {
+        cte.rdbase = (cmdpkt[2] & R_MAPC_RDBASE_MASK) >> R_MAPC_RDBASE_SHIFT;
+        cte.rdbase &= RDBASE_PROCNUM_MASK;
+    } else {
+        cte.rdbase = 0;
+    }
 
-    if ((icid >= s->ct.num_entries) || (cte.rdbase >= s->gicv3->num_cpu)) {
+    if (icid >= s->ct.num_entries) {
+        qemu_log_mask(LOG_GUEST_ERROR, "ITS MAPC: invalid ICID 0x%d", icid);
+        return CMD_CONTINUE;
+    }
+    if (cte.valid && cte.rdbase >= s->gicv3->num_cpu) {
         qemu_log_mask(LOG_GUEST_ERROR,
-                      "ITS MAPC: invalid collection table attributes "
-                      "icid %d rdbase %u\n",  icid, cte.rdbase);
-        /*
-         * in this implementation, in case of error
-         * we ignore this command and move onto the next
-         * command in the queue
-         */
+                      "ITS MAPC: invalid RDBASE %u ", cte.rdbase);
         return CMD_CONTINUE;
     }