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x86, microcode: Add a disable chicken bit

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Add a cmdline param which disables the microcode loader. This is useful
mostly in debugging situations where we want to turn off microcode
loading, both early from the initrd and late, as a means to be able to
rule out its influence on the machine.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1400525957-11525-3-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Borislav Petkov 2014-05-19 20:59:17 +02:00 • committed by H. Peter Anvin
commit 65cef1311d
3 changed files with 44 additions and 0 deletions
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1
arch/x86/include/asm/microcode.h
View file

@ -25,6 +25,7 @@ struct cpu_signature {
struct device;
enum ucode_state { UCODE_ERROR, UCODE_OK, UCODE_NFOUND };
extern bool dis_ucode_ldr;
struct microcode_ops {
enum ucode_state (*request_microcode_user) (int cpu,

6
arch/x86/kernel/cpu/microcode/core.c
View file

@ -97,6 +97,9 @@ MODULE_LICENSE("GPL");
static struct microcode_ops *microcode_ops;
bool dis_ucode_ldr;
module_param(dis_ucode_ldr, bool, 0);
/*
* Synchronization.
*
@ -546,6 +549,9 @@ static int __init microcode_init(void)
struct cpuinfo_x86 *c = &cpu_data(0);
int error;
if (dis_ucode_ldr)
return 0;
if (c->x86_vendor == X86_VENDOR_INTEL)
microcode_ops = init_intel_microcode();
else if (c->x86_vendor == X86_VENDOR_AMD)

37
arch/x86/kernel/cpu/microcode/core_early.c
View file

@ -17,9 +17,11 @@
* 2 of the License, or (at your option) any later version.
*/
#include <linux/module.h>
#include <asm/microcode.h>
#include <asm/microcode_intel.h>
#include <asm/microcode_amd.h>
#include <asm/processor.h>
#include <asm/cmdline.h>
#define QCHAR(a, b, c, d) ((a) + ((b) << 8) + ((c) << 16) + ((d) << 24))
#define CPUID_INTEL1 QCHAR('G', 'e', 'n', 'u')
@ -72,10 +74,33 @@ static int x86_family(void)
return x86;
}
static bool __init check_loader_disabled_bsp(void)
{
#ifdef CONFIG_X86_32
const char *cmdline = (const char *)__pa_nodebug(boot_command_line);
const char *opt = "dis_ucode_ldr";
const char *option = (const char *)__pa_nodebug(opt);
bool *res = (bool *)__pa_nodebug(&dis_ucode_ldr);
#else /* CONFIG_X86_64 */
const char *cmdline = boot_command_line;
const char *option = "dis_ucode_ldr";
bool *res = &dis_ucode_ldr;
#endif
if (cmdline_find_option_bool(cmdline, option))
*res = true;
return *res;
}
void __init load_ucode_bsp(void)
{
int vendor, x86;
if (check_loader_disabled_bsp())
return;
if (!have_cpuid_p())
return;
@ -96,10 +121,22 @@ void __init load_ucode_bsp(void)
}
}
static bool check_loader_disabled_ap(void)
{
#ifdef CONFIG_X86_32
return __pa_nodebug(dis_ucode_ldr);
#else
return dis_ucode_ldr;
#endif
}
void load_ucode_ap(void)
{
int vendor, x86;
if (check_loader_disabled_ap())
return;
if (!have_cpuid_p())
return;