cpu/hotplug: Expose SMT control init function

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@suse.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20180713142323.039715135@linutronix.de
Orabug: 28220674
CVE: CVE-2018-3620

(cherry picked from commit 8e1b706b6e819bed215c0db16345568864660393)

Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Conflicts:
	kernel/cpu.c
Contextual: different content

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 3c58810123e4e0bcbef6bae2fbeb9ddc8ae57b6f..3553419e862788208aacee1438999a8584be5200 100644 (file)
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -317,8 +317,10 @@ 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_ */

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 66994587ccb90c54751de6521c2179c913e2ee5c..3e609b4275d59891eb9e52d13ad38ad90b224f39 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -499,13 +499,23 @@ void __cpuinit smpboot_thread_init(void)
 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);