target/ppc: Enforce that the root page directory size must be at least 5

According to the ISA the root page directory size of a radix tree for
either process- or partition-scoped translation must be >= 5.

Thus add this to the list of conditions checked when validating the
partition table entry in validate_pate();

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20200330094946.24678-2-clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

target/ppc/mmu-radix64.c

@@ -212,6 +212,9 @@ static bool validate_pate(PowerPCCPU *cpu, uint64_t lpid, ppc_v3_pate_t *pate)
     if (lpid == 0 && !msr_hv) {
         return false;
     }
+    if ((pate->dw0 & PATE1_R_PRTS) < 5) {
+        return false;
+    }
     /* More checks ... */
     return true;
 }