c_p_a(): do a simple self test at boot

When CONFIG_DEBUG_RODATA is enabled undo the ro mapping and redo it again.
This gives some simple testing for change_page_attr().
Signed-off-by: Andi Kleen <ak@suse.de>
Acked-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/Kconfig.debug

@@ -204,4 +204,9 @@ config DEBUG_BOOT_PARAMS
 	help
 	  This option will cause struct boot_params to be exported via debugfs.
 
+config CPA_DEBUG
+	bool "CPA self test code"
+	help
+	  Do change_page_attr self tests at boot.
+
 endmenu

arch/x86/mm/init_32.c

@@ -799,6 +799,20 @@ void mark_rodata_ro(void)
 		change_page_attr(virt_to_page(start),
 		                 size >> PAGE_SHIFT, PAGE_KERNEL_RX);
 		printk("Write protecting the kernel text: %luk\n", size >> 10);
+
+#ifdef CONFIG_CPA_DEBUG
+		global_flush_tlb();
+
+		printk("Testing CPA: Reverting %lx-%lx\n", start, start+size);
+		change_page_attr(virt_to_page(start), size>>PAGE_SHIFT,
+				 PAGE_KERNEL_EXEC);
+		global_flush_tlb();
+
+		printk("Testing CPA: write protecting again\n");
+		change_page_attr(virt_to_page(start), size>>PAGE_SHIFT,
+				PAGE_KERNEL_RX);
+		global_flush_tlb();
+#endif
 	}
 #endif
 	start += size;
@@ -815,6 +829,18 @@ void mark_rodata_ro(void)
 	 * of who is the culprit.
 	 */
 	global_flush_tlb();
+
+#ifdef CONFIG_CPA_DEBUG
+	printk("Testing CPA: undo %lx-%lx\n", start, start + size);
+	change_page_attr(virt_to_page(start), size >> PAGE_SHIFT,
+				PAGE_KERNEL);
+	global_flush_tlb();
+
+	printk("Testing CPA: write protecting again\n");
+	change_page_attr(virt_to_page(start), size >> PAGE_SHIFT,
+				PAGE_KERNEL_RO);
+	global_flush_tlb();
+#endif
 }
 #endif
 

arch/x86/mm/init_64.c

@@ -606,6 +606,16 @@ void mark_rodata_ro(void)
 	 * of who is the culprit.
 	 */
 	global_flush_tlb();
+
+#ifdef CONFIG_CPA_DEBUG
+	printk("Testing CPA: undo %lx-%lx\n", start, end);
+	change_page_attr_addr(start, (end - start) >> PAGE_SHIFT, PAGE_KERNEL);
+	global_flush_tlb();
+
+	printk("Testing CPA: again\n");
+	change_page_attr_addr(start, (end - start) >> PAGE_SHIFT, PAGE_KERNEL_RO);
+	global_flush_tlb();
+#endif
 }
 #endif