Set the XN bit for the device areas

The XN bit has to be set to avoid speculative prefetch from the device
mappings on newer architectures (post ARMv6).
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm/kernel/head.S

@@ -274,6 +274,10 @@ __create_page_tables:
 #ifdef CONFIG_DEBUG_LL
 	bic	r7, r7, #0x0c			@ turn off cacheable
 						@ and bufferable bits
+#if __LINUX_ARM_ARCH__ >= 6
+	orr	r7, r7, #(1 << 4)		@ must set XN to avoid
+						@ speculative prefetch
+#endif
 	/*
 	 * Map in IO space for serial debugging.
 	 * This allows debug messages to be output

arch/arm/mm/mm-armv.c

@@ -420,9 +420,11 @@ void __init build_mem_type_table(void)
 
 		/*
 		 * Mark the device area as "shared device"
+		 * Bit 4 (execute-never) has to be set to avoid
+		 * speculative prefetching
 		 */
 		mem_types[MT_DEVICE].prot_pte |= L_PTE_BUFFERABLE;
-		mem_types[MT_DEVICE].prot_sect |= PMD_SECT_BUFFERED;
+		mem_types[MT_DEVICE].prot_sect |= PMD_SECT_BUFFERED|PMD_BIT4;
 
 		/*
 		 * User pages need to be mapped with the ASID