/* 
 * Author: Tiago Vignatti <vignatti (at) c3sl ufpr br>
 * 2007 - code under GPL 
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/notifier.h>
#include <linux/kdebug.h>

/* 
 * error_code:
 *      bit 0 == 0 means no page found, 1 means protection fault
 *      bit 1 == 0 means read, 1 means write
 *      bit 2 == 0 means kernel, 1 means user-mode
 *      bit 3 == 1 means use of reserved bit detected
 *      bit 4 == 1 means fault was an instruction fetch
 */
static int pf_notify (struct notifier_block *self,
                                unsigned long val, void *data)
{
	struct die_args *args = (struct die_args *) data;

	/* You can filter the types of page like this: 
	if (args->err < 4)
		return NOTIFY_DONE;
	*/

	printk("pagefault regs: %p, address: 0x%lx, fault: %lx ",
	       args->regs, args->address, args->err);

	switch (args->err) {
		case 7:
			printk("(write protection fault in user-mode)\n");
			break;
		case 6:
			printk("(write page fault in user-mode)\n");
			break;
		case 5:
			printk("(write protection fault in user-mode)\n");
			break;
		case 4:
			printk("(read page fault in user-mode)\n");
			break;
		case 3:
			printk("(write protection fault in kernel-mode)\n");
			break;
		case 2:
			printk("(write page fault in kernel-mode)\n");
			break;
		case 1:
			printk("(read protection fault in kernel-mode)\n");
			break;
		case 0:
			printk("(read page fault in kernel-mode)\n");
			break;
		default :
			printk("(use of reserved bit detected or fault was an instruction fetch)\n");
			break;
	}

	return NOTIFY_DONE;
}

static struct notifier_block my_nb = {
	.notifier_call = pf_notify,
};

static int __init notifier_init(void)
{
	int ret;

	if ((ret = register_page_fault_notifier(&my_nb)) < 0) {
		printk("register_page_fault_notifier failed, returned %d\n", ret);
		return -1;
	}

	printk("Planted page fault notifier!\n");
	return 0;
}

static void __exit notifier_exit(void)
{
	unregister_page_fault_notifier(&my_nb);
	printk("Page fault notifier unregistered\n");
}

module_init(notifier_init)
module_exit(notifier_exit)
MODULE_LICENSE("GPL");