mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-23 07:26:16 +07:00
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>
60 lines
1.6 KiB
C
60 lines
1.6 KiB
C
/*
|
|
* This file is part of the Linux kernel.
|
|
*
|
|
* Copyright (c) 2011, Intel Corporation
|
|
* Authors: Fenghua Yu <fenghua.yu@intel.com>,
|
|
* H. Peter Anvin <hpa@linux.intel.com>
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify it
|
|
* under the terms and conditions of the GNU General Public License,
|
|
* version 2, as published by the Free Software Foundation.
|
|
*
|
|
* This program is distributed in the hope it will be useful, but WITHOUT
|
|
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
|
|
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
|
|
* more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License along with
|
|
* this program; if not, write to the Free Software Foundation, Inc.,
|
|
* 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
|
|
*
|
|
*/
|
|
|
|
#include <asm/processor.h>
|
|
#include <asm/archrandom.h>
|
|
#include <asm/sections.h>
|
|
|
|
static int __init x86_rdrand_setup(char *s)
|
|
{
|
|
setup_clear_cpu_cap(X86_FEATURE_RDRAND);
|
|
setup_clear_cpu_cap(X86_FEATURE_RDSEED);
|
|
return 1;
|
|
}
|
|
__setup("nordrand", x86_rdrand_setup);
|
|
|
|
/*
|
|
* RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
|
|
* Run the instruction a few times as a sanity check.
|
|
* If it fails, it is simple to disable RDRAND here.
|
|
*/
|
|
#define SANITY_CHECK_LOOPS 8
|
|
|
|
void x86_init_rdrand(struct cpuinfo_x86 *c)
|
|
{
|
|
#ifdef CONFIG_ARCH_RANDOM
|
|
unsigned long tmp;
|
|
int i;
|
|
|
|
if (!cpu_has(c, X86_FEATURE_RDRAND))
|
|
return;
|
|
|
|
for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
|
|
if (!rdrand_long(&tmp)) {
|
|
clear_cpu_cap(c, X86_FEATURE_RDRAND);
|
|
printk_once(KERN_WARNING "rdrand: disabled\n");
|
|
return;
|
|
}
|
|
}
|
|
#endif
|
|
}
|