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0007bccc3c
x86_init_rdrand() was added with 2 goals: 1. Sanity check that the built-in-self-test circuit on the Digital Random Number Generator (DRNG) is not complaining. As RDRAND HW self-checks on every invocation, this goal is achieved by simply invoking RDRAND and checking its return code. 2. Force a full re-seed of the random number generator. This was done out of paranoia to benefit the most un-sophisticated DRNG implementation conceivable in the architecture, an implementation that does not exist, and unlikely ever will. This worst-case full-re-seed is achieved by invoking a 64-bit RDRAND 8192 times. Unfortunately, this worst-case re-seed costs O(1,000us). Magnifying this cost, it is done from identify_cpu(), which is the synchronous critical path to bring a processor on-line -- repeated for every logical processor in the system at boot and resume from S3. As it is very expensive, and of highly dubious value, we delete the worst-case re-seed from the kernel. We keep the 1st goal -- sanity check the hardware, and mark it absent if it complains. This change reduces the cost of x86_init_rdrand() by a factor of 1,000x, to O(1us) from O(1,000us). Signed-off-by: Len Brown <len.brown@intel.com> Link: http://lkml.kernel.org/r/058618cc56ec6611171427ad7205e37e377aa8d4.1439738240.git.len.brown@intel.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
59 lines
1.6 KiB
C
59 lines
1.6 KiB
C
/*
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* This file is part of the Linux kernel.
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*
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* Copyright (c) 2011, Intel Corporation
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* Authors: Fenghua Yu <fenghua.yu@intel.com>,
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* H. Peter Anvin <hpa@linux.intel.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms and conditions of the GNU General Public License,
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* version 2, as published by the Free Software Foundation.
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*
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* This program is distributed in the hope it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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* more details.
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*
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* You should have received a copy of the GNU General Public License along with
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* this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
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*
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*/
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#include <asm/processor.h>
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#include <asm/archrandom.h>
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#include <asm/sections.h>
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static int __init x86_rdrand_setup(char *s)
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{
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setup_clear_cpu_cap(X86_FEATURE_RDRAND);
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setup_clear_cpu_cap(X86_FEATURE_RDSEED);
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return 1;
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}
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__setup("nordrand", x86_rdrand_setup);
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/*
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* RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
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* Run the instruction a few times as a sanity check.
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* If it fails, it is simple to disable RDRAND here.
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*/
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#define SANITY_CHECK_LOOPS 8
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void x86_init_rdrand(struct cpuinfo_x86 *c)
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{
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#ifdef CONFIG_ARCH_RANDOM
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unsigned long tmp;
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int i;
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if (!cpu_has(c, X86_FEATURE_RDRAND))
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return;
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for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
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if (!rdrand_long(&tmp)) {
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clear_cpu_cap(c, X86_FEATURE_RDRAND);
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printk_once(KERN_WARNING "rdrand: disabled\n");
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return;
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}
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}
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#endif
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}
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