[PATCH 4.9 076/107] cpu/hotplug: Expose SMT control init function

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Kosina <jkosina@xxxxxxx>

commit 8e1b706b6e819bed215c0db16345568864660393 upstream

The L1TF mitigation will gain a commend line parameter which allows to set
a combination of hypervisor mitigation and SMT control.

Expose cpu_smt_disable() so the command line parser can tweak SMT settings.

[ tglx: Split out of larger patch and made it preserve an already existing
  	force off state ]

Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Jiri Kosina <jkosina@xxxxxxx>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20180713142323.039715135@xxxxxxxxxxxxx
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/cpu.h |    2 ++
 kernel/cpu.c        |   16 +++++++++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)

--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -266,8 +266,10 @@ enum cpuhp_smt_control {
 
 #if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT)
 extern enum cpuhp_smt_control cpu_smt_control;
+extern void cpu_smt_disable(bool force);
 #else
 # define cpu_smt_control		(CPU_SMT_ENABLED)
+static inline void cpu_smt_disable(bool force) { }
 #endif
 
 #endif /* _LINUX_CPU_H_ */
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -360,13 +360,23 @@ EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
 enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
 EXPORT_SYMBOL_GPL(cpu_smt_control);
 
-static int __init smt_cmdline_disable(char *str)
+void __init cpu_smt_disable(bool force)
 {
-	cpu_smt_control = CPU_SMT_DISABLED;
-	if (str && !strcmp(str, "force")) {
+	if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
+		cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
+		return;
+
+	if (force) {
 		pr_info("SMT: Force disabled\n");
 		cpu_smt_control = CPU_SMT_FORCE_DISABLED;
+	} else {
+		cpu_smt_control = CPU_SMT_DISABLED;
 	}
+}
+
+static int __init smt_cmdline_disable(char *str)
+{
+	cpu_smt_disable(str && !strcmp(str, "force"));
 	return 0;
 }
 early_param("nosmt", smt_cmdline_disable);