x86/Kconfig: Select SCHED_SMT if SMP enabled

CONFIG_SCHED_SMT is enabled by all distros, so there is not a real point to
have it configurable. The runtime overhead in the core scheduler code is
minimal because the actual SMT scheduling parts are conditional on a static
key.

This allows to expose the scheduler's SMT state static key to the
speculation control code. Alternatively the scheduler's static key could be
made always available when CONFIG_SMP is enabled, but that's just adding an
unused static key to every other architecture for nothing.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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 <jkosina@suse.cz>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Casey Schaufler <casey.schaufler@intel.com>
Cc: Asit Mallick <asit.k.mallick@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Waiman Long <longman9394@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Dave Stewart <david.c.stewart@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181125185004.337452245@linutronix.de
CVE-2017-5715

(cherry picked from commit dbe733642e01dd108f71436aaea7b328cb28fd87)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2a076173aad8b1b585d22b9a08fdc2a185be1e70..8bb9851d0d3a8aa55d97698e432839aacf807101 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -961,13 +961,7 @@ config NR_CPUS
          approximately eight kilobytes to the kernel image.
 
 config SCHED_SMT
-       bool "SMT (Hyperthreading) scheduler support"
-       depends on SMP
-       ---help---
-         SMT scheduler support improves the CPU scheduler's decision making
-         when dealing with Intel Pentium 4 chips with HyperThreading at a
-         cost of slightly increased overhead in some places. If unsure say
-         N here.
+       def_bool y if SMP
 
 config SCHED_MC
        def_bool y