1/*
2 * This file is part of the Linux kernel.
3 *
4 * Copyright (c) 2011, Intel Corporation
5 * Authors: Fenghua Yu <fenghua.yu@intel.com>,
6 *          H. Peter Anvin <hpa@linux.intel.com>
7 *
8 * This program is free software; you can redistribute it and/or modify it
9 * under the terms and conditions of the GNU General Public License,
10 * version 2, as published by the Free Software Foundation.
11 *
12 * This program is distributed in the hope it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
15 * more details.
16 *
17 * You should have received a copy of the GNU General Public License along with
18 * this program; if not, write to the Free Software Foundation, Inc.,
19 * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 */
22
23#include <asm/processor.h>
24#include <asm/archrandom.h>
25#include <asm/sections.h>
26
27static int __init x86_rdrand_setup(char *s)
28{
29	setup_clear_cpu_cap(X86_FEATURE_RDRAND);
30	setup_clear_cpu_cap(X86_FEATURE_RDSEED);
31	return 1;
32}
33__setup("nordrand", x86_rdrand_setup);
34
35/*
36 * Force a reseed cycle; we are architecturally guaranteed a reseed
37 * after no more than 512 128-bit chunks of random data.  This also
38 * acts as a test of the CPU capability.
39 */
40#define RESEED_LOOP ((512*128)/sizeof(unsigned long))
41
42void x86_init_rdrand(struct cpuinfo_x86 *c)
43{
44#ifdef CONFIG_ARCH_RANDOM
45	unsigned long tmp;
46	int i, count, ok;
47
48	if (!cpu_has(c, X86_FEATURE_RDRAND))
49		return;		/* Nothing to do */
50
51	for (count = i = 0; i < RESEED_LOOP; i++) {
52		ok = rdrand_long(&tmp);
53		if (ok)
54			count++;
55	}
56
57	if (count != RESEED_LOOP)
58		clear_cpu_cap(c, X86_FEATURE_RDRAND);
59#endif
60}
61