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x86: add generic clearcpuid=... option

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Add a generic option to clear any cpuid bit. I added it because it was
very easy to add with the new generic cpuid disable bitmap and perhaps
it will be useful in the future.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Andi Kleen 2008-01-30 13:33:21 +01:00 committed by Ingo Molnar
parent 191679fdfa
commit ac72e7888a
3 changed files with 35 additions and 0 deletions
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13
Documentation/kernel-parameters.txt
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@ -416,6 +416,19 @@ and is between 256 and 4096 characters. It is defined in the file
[SPARC64] tick
[X86-64] hpet,tsc
clearcpuid=BITNUM [X86]
Disable CPUID feature X for the kernel. See
include/asm-x86/cpufeature.h for the valid bit numbers.
Note the Linux specific bits are not necessarily
stable over kernel options, but the vendor specific
ones should be.
Also note that user programs calling CPUID directly
or using the feature without checking anything
will still see it. This just prevents it from
being used by the kernel or shown in /proc/cpuinfo.
Also note the kernel might malfunction if you disable
some critical bits.
code_bytes [IA32/X86_64] How many bytes of object code to print
in an oops report.
Range: 0 - 8192

11
arch/x86/kernel/cpu/common.c
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@ -572,6 +572,17 @@ void __cpuinit print_cpu_info(struct cpuinfo_x86 *c)
printk("\n");
}
static __init int setup_disablecpuid(char *arg)
{
int bit;
if (get_option(&arg, &bit) && bit < NCAPINTS*32)
setup_clear_cpu_cap(bit);
else
return 0;
return 1;
}
__setup("clearcpuid=", setup_disablecpuid);
cpumask_t cpu_initialized __cpuinitdata = CPU_MASK_NONE;
/* This is hacky. :)

11
arch/x86/kernel/setup_64.c
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@ -1050,6 +1050,17 @@ void __cpuinit print_cpu_info(struct cpuinfo_x86 *c)
printk(KERN_CONT "\n");
}
static __init int setup_disablecpuid(char *arg)
{
int bit;
if (get_option(&arg, &bit) && bit < NCAPINTS*32)
setup_clear_cpu_cap(bit);
else
return 0;
return 1;
}
__setup("clearcpuid=", setup_disablecpuid);
/*
* Get CPU information for use by the procfs.
*/