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[PATCH] i386: allow disabling X86_FEATURE_SEP at boot

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Allow the x86 "sep" feature to be disabled at bootup.  This forces use of the
int80 vsyscall.  Mainly for testing or benchmarking the int80 vsyscall code.

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Chuck Ebbert 2006-03-23 02:59:34 -08:00 committed by Linus Torvalds
parent 3bc9b76bed
commit 4f88651125
2 changed files with 19 additions and 2 deletions
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6
Documentation/kernel-parameters.txt
View file

@ -1008,7 +1008,9 @@ running once the system is up.
noexec=on: enable non-executable mappings (default)
noexec=off: disable nn-executable mappings
nofxsr [BUGS=IA-32]
nofxsr [BUGS=IA-32] Disables x86 floating point extended
register save and restore. The kernel will only save
legacy floating-point registers on task switch.
nohlt [BUGS=ARM]
@ -1053,6 +1055,8 @@ running once the system is up.
nosbagart [IA-64]
nosep [BUGS=IA-32] Disables x86 SYSENTER/SYSEXIT support.
nosmp [SMP] Tells an SMP kernel to act as a UP kernel.
nosync [HW,M68K] Disables sync negotiation for all devices.

15
arch/i386/kernel/cpu/common.c
View file

@ -26,8 +26,9 @@ DEFINE_PER_CPU(unsigned char, cpu_16bit_stack[CPU_16BIT_STACK_SIZE]);
EXPORT_PER_CPU_SYMBOL(cpu_16bit_stack);
static int cachesize_override __cpuinitdata = -1;
static int disable_x86_fxsr __cpuinitdata = 0;
static int disable_x86_fxsr __cpuinitdata;
static int disable_x86_serial_nr __cpuinitdata = 1;
static int disable_x86_sep __cpuinitdata;
struct cpu_dev * cpu_devs[X86_VENDOR_NUM] = {};
@ -187,6 +188,14 @@ static int __init x86_fxsr_setup(char * s)
__setup("nofxsr", x86_fxsr_setup);
static int __init x86_sep_setup(char * s)
{
disable_x86_sep = 1;
return 1;
}
__setup("nosep", x86_sep_setup);
/* Standard macro to see if a specific flag is changeable */
static inline int flag_is_changeable_p(u32 flag)
{
@ -405,6 +414,10 @@ void __cpuinit identify_cpu(struct cpuinfo_x86 *c)
clear_bit(X86_FEATURE_XMM, c->x86_capability);
}
/* SEP disabled? */
if (disable_x86_sep)
clear_bit(X86_FEATURE_SEP, c->x86_capability);
if (disable_pse)
clear_bit(X86_FEATURE_PSE, c->x86_capability);