hw/intc/arm_gicv3: GICD_TYPER.SecurityExtn is RAZ if GICD_CTLR.DS == 1

The GICv3 specification says that the GICD_TYPER.SecurityExtn bit
is RAZ if GICD_CTLR.DS is 1. We were incorrectly making it RAZ
if the security extension is unsupported. "Security extension
unsupported" always implies GICD_CTLR.DS == 1, but the guest can
also set DS on a GIC which does support the security extension.
Fix the condition to correctly check the GICD_CTLR.DS bit.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20190524124248.28394-3-peter.maydell@linaro.org

hw/intc/arm_gicv3_dist.c

@@ -378,8 +378,14 @@ static MemTxResult gicd_readl(GICv3State *s, hwaddr offset,
          * ITLinesNumber == (num external irqs / 32) - 1
          */
         int itlinesnumber = ((s->num_irq - GIC_INTERNAL) / 32) - 1;
+        /*
+         * SecurityExtn must be RAZ if GICD_CTLR.DS == 1, and
+         * "security extensions not supported" always implies DS == 1,
+         * so we only need to check the DS bit.
+         */
+        bool sec_extn = !(s->gicd_ctlr & GICD_CTLR_DS);
 
-        *data = (1 << 25) | (1 << 24) | (s->security_extn << 10) |
+        *data = (1 << 25) | (1 << 24) | (sec_extn << 10) |
             (0xf << 19) | itlinesnumber;
         return MEMTX_OK;
     }