x86: add noclflush option

To disable CLFLUSH usage, especially in change_page_attr().
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Documentation/kernel-parameters.txt

@@ -1191,6 +1191,8 @@ and is between 256 and 4096 characters. It is defined in the file
 			register save and restore. The kernel will only save
 			legacy floating-point registers on task switch.
 
+	noclflush	[BUGS=X86] Don't use the CLFLUSH instruction
+
 	nohlt		[BUGS=ARM]
 
 	no-hlt		[BUGS=X86-32] Tells the kernel that the hlt

arch/x86/kernel/cpu/common.c

@@ -542,6 +542,13 @@ void __cpuinit detect_ht(struct cpuinfo_x86 *c)
 }
 #endif
 
+static __init int setup_noclflush(char *arg)
+{
+	setup_clear_cpu_cap(X86_FEATURE_CLFLSH);
+	return 1;
+}
+__setup("noclflush", setup_noclflush);
+
 void __cpuinit print_cpu_info(struct cpuinfo_x86 *c)
 {
 	char *vendor = NULL;

arch/x86/kernel/setup_64.c

@@ -1032,6 +1032,13 @@ void __cpuinit identify_cpu(struct cpuinfo_x86 *c)
 
 }
 
+static __init int setup_noclflush(char *arg)
+{
+	setup_clear_cpu_cap(X86_FEATURE_CLFLSH);
+	return 1;
+}
+__setup("noclflush", setup_noclflush);
+
 void __cpuinit print_cpu_info(struct cpuinfo_x86 *c)
 {
 	if (c->x86_model_id[0])