Merge branch 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull cpu hotplug fixes from Thomas Gleixner:
 "Two fixes for the cpu hotplug machinery:

   - Replace the overly clever 'SMT disabled by BIOS' detection logic as
     it breaks KVM scenarios and prevents speculation control updates
     when the Hyperthreads are brought online late after boot.

   - Remove a redundant invocation of the speculation control update
     function"

* 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  cpu/hotplug: Fix "SMT disabled by BIOS" detection for KVM
  x86/speculation: Remove redundant arch_smt_update() invocation

3 files changed, 6 insertions, 35 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 91d5c38eb7e5..d1c6d152da89 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -376,9 +376,6 @@ 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);
-
-static bool cpu_smt_available __read_mostly;
 
 void __init cpu_smt_disable(bool force)
 {
@@ -397,25 +394,11 @@ void __init cpu_smt_disable(bool force)
 
 /*
  * The decision whether SMT is supported can only be done after the full
- * CPU identification. Called from architecture code before non boot CPUs
- * are brought up.
- */
-void __init cpu_smt_check_topology_early(void)
-{
-	if (!topology_smt_supported())
-		cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
-}
-
-/*
- * If SMT was disabled by BIOS, detect it here, after the CPUs have been
- * brought online. This ensures the smt/l1tf sysfs entries are consistent
- * with reality. cpu_smt_available is set to true during the bringup of non
- * boot CPUs when a SMT sibling is detected. Note, this may overwrite
- * cpu_smt_control's previous setting.
+ * CPU identification. Called from architecture code.
  */
 void __init cpu_smt_check_topology(void)
 {
-	if (!cpu_smt_available)
+	if (!topology_smt_supported())
 		cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
 }
 
@@ -428,18 +411,10 @@ early_param("nosmt", smt_cmdline_disable);
 
 static inline bool cpu_smt_allowed(unsigned int cpu)
 {
-	if (topology_is_primary_thread(cpu))
+	if (cpu_smt_control == CPU_SMT_ENABLED)
 		return true;
 
-	/*
-	 * If the CPU is not a 'primary' thread and the booted_once bit is
-	 * set then the processor has SMT support. Store this information
-	 * for the late check of SMT support in cpu_smt_check_topology().
-	 */
-	if (per_cpu(cpuhp_state, cpu).booted_once)
-		cpu_smt_available = true;
-
-	if (cpu_smt_control == CPU_SMT_ENABLED)
+	if (topology_is_primary_thread(cpu))
 		return true;
 
 	/*
@@ -2090,10 +2065,8 @@ static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
 		 */
 		cpuhp_offline_cpu_device(cpu);
 	}
-	if (!ret) {
+	if (!ret)
 		cpu_smt_control = ctrlval;
-		arch_smt_update();
-	}
 	cpu_maps_update_done();
 	return ret;
 }
@@ -2104,7 +2077,6 @@ static int cpuhp_smt_enable(void)
 
 	cpu_maps_update_begin();
 	cpu_smt_control = CPU_SMT_ENABLED;
-	arch_smt_update();
 	for_each_present_cpu(cpu) {
 		/* Skip online CPUs and CPUs on offline nodes */
 		if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 50aa2aba69bd..310d0637fe4b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5980,6 +5980,7 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p
 
 #ifdef CONFIG_SCHED_SMT
 DEFINE_STATIC_KEY_FALSE(sched_smt_present);
+EXPORT_SYMBOL_GPL(sched_smt_present);
 
 static inline void set_idle_cores(int cpu, int val)
 {
diff --git a/kernel/smp.c b/kernel/smp.c
index 163c451af42e..f4cf1b0bb3b8 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -584,8 +584,6 @@ void __init smp_init(void)
 		num_nodes, (num_nodes > 1 ? "s" : ""),
 		num_cpus,  (num_cpus  > 1 ? "s" : ""));
 
-	/* Final decision about SMT support */
-	cpu_smt_check_topology();
 	/* Any cleanup work */
 	smp_cpus_done(setup_max_cpus);
 }