[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: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fc99075..880be3a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1008,7 +1008,9 @@
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 @@
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.
diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c
index f63dcfb..bbfc278 100644
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -26,8 +26,9 @@
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 @@
__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 @@
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);