x86/speculation: Rework SMT state change

arch_smt_update() is only called when the sysfs SMT control knob is
changed. This means that when SMT is enabled in the sysfs control knob the
system is considered to have SMT active even if all siblings are offline.

To allow finegrained control of the speculation mitigations, the actual SMT
state is more interesting than the fact that siblings could be enabled.

Rework the code, so arch_smt_update() is invoked from each individual CPU
hotplug function, and simplify the update function while at it.

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/20181125185004.521974984@linutronix.de

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index a723af0c440087a98b426a687a3e53b877a91240..5625b323ff329e2e9d4f46cdf313bc4212d6fce6 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -14,6 +14,7 @@
 #include <linux/module.h>
 #include <linux/nospec.h>
 #include <linux/prctl.h>
+#include <linux/sched/smt.h>
 
 #include <asm/spec-ctrl.h>
 #include <asm/cmdline.h>
@@ -344,16 +345,14 @@ void arch_smt_update(void)
                return;
 
        mutex_lock(&spec_ctrl_mutex);
-       mask = x86_spec_ctrl_base;
-       if (cpu_smt_control == CPU_SMT_ENABLED)
+
+       mask = x86_spec_ctrl_base & ~SPEC_CTRL_STIBP;
+       if (sched_smt_active())
                mask |= SPEC_CTRL_STIBP;
-       else
-               mask &= ~SPEC_CTRL_STIBP;
 
        if (mask != x86_spec_ctrl_base) {
                pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n",
-                               cpu_smt_control == CPU_SMT_ENABLED ?
-                               "Enabling" : "Disabling");
+                       mask & SPEC_CTRL_STIBP ? "Enabling" : "Disabling");
                x86_spec_ctrl_base = mask;
                on_each_cpu(update_stibp_msr, NULL, 1);
        }

diff --git a/include/linux/sched/smt.h b/include/linux/sched/smt.h
index c9e0be51411045b4de65b9e9d3b44de75e27ae88..59d3736c454cf85a7de69181af6377fae7dc10c6 100644 (file)
--- a/include/linux/sched/smt.h
+++ b/include/linux/sched/smt.h
@@ -15,4 +15,6 @@ static __always_inline bool sched_smt_active(void)
 static inline bool sched_smt_active(void) { return false; }
 #endif
 
+void arch_smt_update(void);
+
 #endif

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 3c7f3b4c453cf57c8e37dd5fadc9f5941f074f0d..91d5c38eb7e5b91a5d2cf821414f7cbbaa854c7a 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -10,6 +10,7 @@
 #include <linux/sched/signal.h>
 #include <linux/sched/hotplug.h>
 #include <linux/sched/task.h>
+#include <linux/sched/smt.h>
 #include <linux/unistd.h>
 #include <linux/cpu.h>
 #include <linux/oom.h>
@@ -367,6 +368,12 @@ static void lockdep_release_cpus_lock(void)
 
 #endif /* CONFIG_HOTPLUG_CPU */
 
+/*
+ * Architectures that need SMT-specific errata handling during SMT hotplug
+ * should override this.
+ */
+void __weak arch_smt_update(void) { }
+
 #ifdef CONFIG_HOTPLUG_SMT
 enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
 EXPORT_SYMBOL_GPL(cpu_smt_control);
@@ -1011,6 +1018,7 @@ out:
         * concurrent CPU hotplug via cpu_add_remove_lock.
         */
        lockup_detector_cleanup();
+       arch_smt_update();
        return ret;
 }
 
@@ -1139,6 +1147,7 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
        ret = cpuhp_up_callbacks(cpu, st, target);
 out:
        cpus_write_unlock();
+       arch_smt_update();
        return ret;
 }
 
@@ -2055,12 +2064,6 @@ static void cpuhp_online_cpu_device(unsigned int cpu)
        kobject_uevent(&dev->kobj, KOBJ_ONLINE);
 }
 
-/*
- * Architectures that need SMT-specific errata handling during SMT hotplug
- * should override this.
- */
-void __weak arch_smt_update(void) { };
-
 static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
 {
        int cpu, ret = 0;