From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Mon, 16 Sep 2019 18:22:56 +0200
Subject: cpu/SMT: create and export cpu_smt_possible()
Git-commit: e1572f1d08be57a5412a464cff0712a23cd0b73e
Patch-mainline: v5.4-rc1
References: bsc#1191580 CVE-2022-0001 CVE-2022-0002

KVM needs to know if SMT is theoretically possible, this means it is
supported and not forcefully disabled ('nosmt=force'). Create and
export cpu_smt_possible() answering this question.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Borislav Petkov <bp@suse.de>
---
 include/linux/cpu.h |    2 ++
 kernel/cpu.c        |   11 +++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -190,10 +190,12 @@ enum cpuhp_smt_control {
 extern enum cpuhp_smt_control cpu_smt_control;
 extern void cpu_smt_disable(bool force);
 extern void cpu_smt_check_topology(void);
+extern bool cpu_smt_possible(void);
 #else
 # define cpu_smt_control		(CPU_SMT_ENABLED)
 static inline void cpu_smt_disable(bool force) { }
 static inline void cpu_smt_check_topology(void) { }
+static inline bool cpu_smt_possible(void) { return false; }
 #endif
 
 /*
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -357,8 +357,7 @@ enum cpuhp_smt_control cpu_smt_control _
 
 void __init cpu_smt_disable(bool force)
 {
-	if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
-		cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
+	if (!cpu_smt_possible())
 		return;
 
 	if (force) {
@@ -402,6 +401,14 @@ static inline bool cpu_smt_allowed(unsig
 	 */
 	return !per_cpu(cpuhp_state, cpu).booted_once;
 }
+
+/* Returns true if SMT is not supported of forcefully (irreversibly) disabled */
+bool cpu_smt_possible(void)
+{
+	return cpu_smt_control != CPU_SMT_FORCE_DISABLED &&
+		cpu_smt_control != CPU_SMT_NOT_SUPPORTED;
+}
+EXPORT_SYMBOL_GPL(cpu_smt_possible);
 #else
 static inline bool cpu_smt_allowed(unsigned int cpu) { return true; }
 #endif