//-------------------------------------------------------------------
//	pgfstats.c
//
//	This module installs a kernel function that intercepts all
//	the page-fault exceptions and records statistics which can
//	be viewed by reading the pseudo-file '/proc/pgfstats'.
//
//	NOTE: Written and tested with Linux kernel version 2.4.20.
//
//	programmer: ALLAN CRUSE
//	written on: 16 JAN 2003
//-------------------------------------------------------------------

#define	__KERNEL__
#define	  MODULE  

#include <linux/module.h>	// for init_module() 
#include <linux/proc_fs.h>	// for create_proc_read_entry() 

#define	SUCCESS	0
#define PGF_ID	14

static char modname[] = "pgfstats";
static unsigned long reason[ 8 ];
static unsigned short oldidtr[3], newidtr[3];
static unsigned long long *oldidt, *newidt;
static unsigned long kpage, isr_orig;

static void pgf_intercept( unsigned long *tos )
{	
	int	error_code = tos[ 10 ] & 0x7;
	reason[ error_code ] += 1;
}	

//-------  PAGE-FAULT EXCEPTION-HANDLER  --------//
asmlinkage void isr_page_fault( void );
asm("	.text					");
asm("	.type	isr_page_fault, @function	");
asm("isr_page_fault:				");
asm("	pushal					");
asm("	pushl	%ds				");
asm("	pushl	%es				");
//
asm("	movl	%ss, %eax			");
asm("	movl	%eax, %ds			");
asm("	movl	%eax, %es			");
//
asm("	pushl	%esp				");
asm("	call	pgf_intercept			");
asm("	addl	$4, %esp			");
//
asm("	popl	%es				");
asm("	popl	%ds				");
asm("	popal					");
asm("	jmp	*isr_orig			");
//-----------------------------------------------//

static int my_proc_read( char *buf, char **start, off_t off,
			int count, int *eof, void *data )
{
	int	i, len;

	len = 0;
	len += sprintf( buf+len, "\nPage-Faults Summary\n" );
	len += sprintf( buf+len, "\nReason  Occurrences\n" );
	
	for (i = 0; i < 8; i++)
		{
		len += sprintf( buf+len, " %d%d%d:", (i>>2)&1, (i>>1)&1, i&1 );
		len += sprintf( buf+len, " %8d ", reason[ i ] );
		len += sprintf( buf+len, "\n" );
		}
	len += sprintf( buf+len, "\n" );

	*eof = 1;
	return	len;
}


static void load_IDTR( void *regimage )
{	
	asm(" lidt %0 " : : "m" (*(unsigned short*)regimage) );
}

int init_module( void )
{
	unsigned long long	gate_desc;
	
	printk( "<1>\nInstalling \'%s\' module\n", modname );

	// allocate kernel memory for the new IDT
	if ( !( kpage = get_free_page( GFP_KERNEL ) ) ) return -ENOMEM;

	// initialize our new IDT and exception-handler
	asm(" sidt oldidtr ; sidt newidtr ");
	memcpy( newidtr+1, &kpage, sizeof( kpage ) );
	oldidt = (unsigned long long*)(*(unsigned long*)(oldidtr+1));
	newidt = (unsigned long long*)(*(unsigned long*)(newidtr+1));
	memcpy( newidt, oldidt, 256 * sizeof( unsigned long long ) );
	
	gate_desc = oldidt[ PGF_ID ];
	gate_desc &= 0xFFFF00000000FFFF;
	gate_desc |= ( gate_desc >> 32 );
	isr_orig = (unsigned long)gate_desc;	
	
	gate_desc = (unsigned long long)isr_page_fault;
	gate_desc &= 0x00000000FFFFFFFF;
	gate_desc |= ( gate_desc << 32 );
	gate_desc &= 0xFFFF00000000FFFF;
	gate_desc |= 0x00008E0000100000;
	newidt[ PGF_ID ] = gate_desc;
	
	// activate the new IDT
	load_IDTR( newidtr );
	smp_call_function( load_IDTR, newidtr, 1, 1 );
	
	// create the proc-file
	create_proc_read_entry( modname, 0, NULL, my_proc_read, NULL );

	return	SUCCESS;
}


void cleanup_module( void )
{
	remove_proc_entry( modname, NULL );

	smp_call_function( load_IDTR, oldidtr, 1, 1 );
	load_IDTR( oldidtr );
	
	if ( kpage ) free_page( kpage );
	printk( "<1>Removing \'%s\' module\n", modname );
}


MODULE_LICENSE("GPL");