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49d859d7 PA |
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 | ||
27 | static int __init x86_rdrand_setup(char *s) | |
28 | { | |
29 | setup_clear_cpu_cap(X86_FEATURE_RDRAND); | |
30 | return 1; | |
31 | } | |
32 | __setup("nordrand", x86_rdrand_setup); | |
33 | ||
34 | /* We can't use arch_get_random_long() here since alternatives haven't run */ | |
35 | static inline int rdrand_long(unsigned long *v) | |
36 | { | |
37 | int ok; | |
38 | asm volatile("1: " RDRAND_LONG "\n\t" | |
39 | "jc 2f\n\t" | |
40 | "decl %0\n\t" | |
41 | "jnz 1b\n\t" | |
42 | "2:" | |
43 | : "=r" (ok), "=a" (*v) | |
44 | : "0" (RDRAND_RETRY_LOOPS)); | |
45 | return ok; | |
46 | } | |
47 | ||
48 | /* | |
49 | * Force a reseed cycle; we are architecturally guaranteed a reseed | |
50 | * after no more than 512 128-bit chunks of random data. This also | |
51 | * acts as a test of the CPU capability. | |
52 | */ | |
53 | #define RESEED_LOOP ((512*128)/sizeof(unsigned long)) | |
54 | ||
148f9bb8 | 55 | void x86_init_rdrand(struct cpuinfo_x86 *c) |
49d859d7 PA |
56 | { |
57 | #ifdef CONFIG_ARCH_RANDOM | |
58 | unsigned long tmp; | |
59 | int i, count, ok; | |
60 | ||
61 | if (!cpu_has(c, X86_FEATURE_RDRAND)) | |
62 | return; /* Nothing to do */ | |
63 | ||
64 | for (count = i = 0; i < RESEED_LOOP; i++) { | |
65 | ok = rdrand_long(&tmp); | |
66 | if (ok) | |
67 | count++; | |
68 | } | |
69 | ||
70 | if (count != RESEED_LOOP) | |
71 | clear_cpu_cap(c, X86_FEATURE_RDRAND); | |
72 | #endif | |
73 | } |