[Patch v5 09/16] x86/smt: Convert cpu_smt_control check to cpu_smt_enabled static key

[Tim Chen]

The checks to cpu_smt_control outside of kernel/cpu.c can be converted
to use cpu_smt_enabled key to run SMT specific code.

Save the export of cpu_smt_control and convert usage of cpu_smt_control
to cpu_smt_enabled outside of kernel/cpu.c.

Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/bugs.c | 21 +++++++++++++++------
 arch/x86/kvm/vmx.c         |  2 +-
 include/linux/cpu.h        |  8 --------
 kernel/cpu.c               |  9 ++++++++-
 4 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index e4cfc4a..6e1b910 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -356,15 +356,16 @@ void arch_smt_update(void)
 
 	mutex_lock(&spec_ctrl_mutex);
 	mask = x86_spec_ctrl_base;
-	if (cpu_smt_control == CPU_SMT_ENABLED)
+	if (static_branch_likely(&cpu_smt_enabled))
 		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");
+		if (static_branch_likely(&cpu_smt_enabled))
+			pr_info("Spectre v2 cross-process SMT mitigation: Enabling STIBP\n");
+		else
+			pr_info("Spectre v2 cross-process SMT mitigation: Disabling STIBP\n");
 		x86_spec_ctrl_base = mask;
 		on_each_cpu(update_stibp_msr, NULL, 1);
 	}
@@ -840,6 +841,14 @@ static const char *l1tf_vmx_states[] = {
 	[VMENTER_L1D_FLUSH_NOT_REQUIRED]	= "flush not necessary"
 };
 
+static char *l1tf_show_smt_vulnerable(void)
+{
+	if (static_branch_likely(&cpu_smt_enabled))
+		return "vulnerable";
+	else
+		return "disabled";
+}
+
 static ssize_t l1tf_show_state(char *buf)
 {
 	if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_AUTO)
@@ -847,13 +856,13 @@ static ssize_t l1tf_show_state(char *buf)
 
 	if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_EPT_DISABLED ||
 	    (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_NEVER &&
-	     cpu_smt_control == CPU_SMT_ENABLED))
+	     static_branch_likely(&cpu_smt_enabled)))
 		return sprintf(buf, "%s; VMX: %s\n", L1TF_DEFAULT_MSG,
 			       l1tf_vmx_states[l1tf_vmx_mitigation]);
 
 	return sprintf(buf, "%s; VMX: %s, SMT %s\n", L1TF_DEFAULT_MSG,
 		       l1tf_vmx_states[l1tf_vmx_mitigation],
-		       cpu_smt_control == CPU_SMT_ENABLED ? "vulnerable" : "disabled");
+		       l1tf_show_smt_vulnerable());
 }
 #else
 static ssize_t l1tf_show_state(char *buf)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4555077..accfd2c 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -11607,7 +11607,7 @@ static int vmx_vm_init(struct kvm *kvm)
 			 * Warn upon starting the first VM in a potentially
 			 * insecure environment.
 			 */
-			if (cpu_smt_control == CPU_SMT_ENABLED)
+			if (static_branch_likely(&cpu_smt_enabled))
 				pr_warn_once(L1TF_MSG_SMT);
 			if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_NEVER)
 				pr_warn_once(L1TF_MSG_L1D);
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index b54f085..00af2ae 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -170,15 +170,7 @@ void cpuhp_report_idle_dead(void);
 static inline void cpuhp_report_idle_dead(void) { }
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 
-enum cpuhp_smt_control {
-	CPU_SMT_ENABLED,
-	CPU_SMT_DISABLED,
-	CPU_SMT_FORCE_DISABLED,
-	CPU_SMT_NOT_SUPPORTED,
-};
-
 #if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT)
-extern enum cpuhp_smt_control cpu_smt_control;
 extern void cpu_smt_disable(bool force);
 extern void cpu_smt_check_topology_early(void);
 extern void cpu_smt_check_topology(void);
diff --git a/kernel/cpu.c b/kernel/cpu.c
index e216154..54cf3f6 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -368,8 +368,15 @@ static void lockdep_release_cpus_lock(void)
 #endif	/* CONFIG_HOTPLUG_CPU */
 
 #ifdef CONFIG_HOTPLUG_SMT
+
+enum cpuhp_smt_control {
+        CPU_SMT_ENABLED,
+        CPU_SMT_DISABLED,
+        CPU_SMT_FORCE_DISABLED,
+        CPU_SMT_NOT_SUPPORTED,
+};
+
 enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
-EXPORT_SYMBOL_GPL(cpu_smt_control);
 DEFINE_STATIC_KEY_TRUE(cpu_smt_enabled);
 EXPORT_SYMBOL_GPL(cpu_smt_enabled);
 
-- 
2.9.4