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Commit 4f886511 authored by Chuck Ebbert's avatar Chuck Ebbert Committed by Linus Torvalds
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[PATCH] i386: allow disabling X86_FEATURE_SEP at boot 



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: default avatarChuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 3bc9b76b

Documentation/kernel-parameters.txt

+5 −1
Original line number Diff line number Diff line
@@ -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.

arch/i386/kernel/cpu/common.c

+14 −1
Original line number Diff line number Diff line
@@ -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);