[PATCH 4.19 042/139] sched/smt: Expose sched_smt_present static key

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

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

From: Thomas Gleixner tglx@linutronix.de

commit 321a874a7ef85655e93b3206d0f36b4a6097f948 upstream

Make the scheduler's 'sched_smt_present' static key globaly available, so
it can be used in the x86 speculation control code.

Provide a query function and a stub for the CONFIG_SMP=n case.

Signed-off-by: Thomas Gleixner <redacted>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jiri Kosina <redacted>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Josh Poimboeuf <redacted>
Cc: Andrea Arcangeli <redacted>
Cc: David Woodhouse <redacted>
Cc: Tim Chen <redacted>
Cc: Andi Kleen <redacted>
Cc: Dave Hansen <redacted>
Cc: Casey Schaufler <redacted>
Cc: Asit Mallick <redacted>
Cc: Arjan van de Ven <redacted>
Cc: Jon Masters <redacted>
Cc: Waiman Long <redacted>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Dave Stewart <redacted>
Cc: Kees Cook <redacted>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181125185004.430168326@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/sched/smt.h |   18 ++++++++++++++++++
 kernel/sched/sched.h      |    4 +---
 2 files changed, 19 insertions(+), 3 deletions(-)

--- /dev/null
+++ b/include/linux/sched/smt.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_SCHED_SMT_H
+#define _LINUX_SCHED_SMT_H
+
+#include <linux/static_key.h>
+
+#ifdef CONFIG_SCHED_SMT
+extern struct static_key_false sched_smt_present;
+
+static __always_inline bool sched_smt_active(void)
+{
+	return static_branch_likely(&sched_smt_present);
+}
+#else
+static inline bool sched_smt_active(void) { return false; }
+#endif
+
+#endif
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h

@@ -23,6 +23,7 @@
 #include <linux/sched/prio.h>
 #include <linux/sched/rt.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/smt.h>
 #include <linux/sched/stat.h>
 #include <linux/sched/sysctl.h>
 #include <linux/sched/task.h>

@@ -930,9 +931,6 @@ static inline int cpu_of(struct rq *rq)
 
 
 #ifdef CONFIG_SCHED_SMT
-
-extern struct static_key_false sched_smt_present;
-
 extern void __update_idle_core(struct rq *rq);
 
 static inline void update_idle_core(struct rq *rq)