MIPS: mm: Panic if an XPA kernel is run without RIXI

XPA kernels hardcode for the presence of RIXI - the PTE format & its
handling presume RI & XI bits. Make this dependence explicit by panicing
if we run on a system that violates it.
Signed-off-by: NPaul Burton <paul.burton@imgtec.com>
Reviewed-by: NJames Hogan <james.hogan@imgtec.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13125/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/mm/tlbex.c

@@ -2508,6 +2508,9 @@ void build_tlb_refill_handler(void)
 	 */
 	static int run_once = 0;
 
+	if (config_enabled(CONFIG_XPA) && !cpu_has_rixi)
+		panic("Kernels supporting XPA currently require CPUs with RIXI");
+
 	output_pgtable_bits_defines();
 	check_pabits();