/* -*- linux-c -*-
 * 
 * Try to trigger DRAM disturbance errors, as described in
 *
 * https://www.ece.cmu.edu/~safari/pubs/kim-isca14.pdf
 *
 * Copyright 2014 Pavel Machek <pavel@ucw.cz>, GPLv2+.
 *
 * You need to run this on cca 2GB machine, or adjust size below. 
 * CONFIG_STRICT_DEVMEM must not be set.
 * Boot with "nopat mem=2G"
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

void disturb(char *w1, char *w2)
{
	/* As far as I could tell... this loop should be run for
	   cca 128msec, to run for one full refresh cycle. */
	
	unsigned int i;
	for (i=0; i< 672000; i++) {
		__asm__ __volatile__(
			"movl 0(%0), %%eax 		\n"	\
			"movl 0(%1), %%eax		\n"	\
			"clflush 0(%0)			\n"	\
			"clflush 0(%1)			\n"	\
			"mfence"
			:: "r" (w1), "r" (w2)
			: "eax"
			);
	}
}

int main(int argc, char *argv[])
{
	/* Ok, so we have one memory for checking, but we do need direct access
	   to /dev/mem to access physical memory.

	   /* This needs at least 2GB RAM machine */
	long size = 1*1024*1024*1024;
	long i;
	unsigned char *mem, *map;
	int fd;

	if (size & (size-1)) {
		printf("Need power of two size\n");
		return 1;
	}
	
	mem = malloc(size);
	memset(mem, 0xff, size);

	fd = open("/dev/mem", O_RDONLY);
//	fd = open("/tmp/delme", O_RDONLY);

	errno = 0;
	/* We want to avoid low 1MB */
	map = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 1*1024*1024);
	if (errno) {
		printf("Can not mmap ram: %m\n");
		return 1;
	}
	/* DRAM operates by whole cachelines, so it should not matter
	   which byte in cacheline we access.
	*/

#define MEG8 (8*1024*1024)
	
	for (i=0; i<(size-MEG8)/100; i+=4096-64)
		disturb(map+i, map+i+MEG8);

	for (i=0; i<size; i++)
		if (mem[i] != 0xff)
			printf("At %lx, got %x\n", i, mem[i]);
}