linux-kernel - [PATCH 1/3] cpu/SMT: create and export cpu_smt

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Date:   Mon, 16 Sep 2019 18:22:56 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Roman Kagan <rkagan@...tuozzo.com>
Subject: [PATCH 1/3] cpu/SMT: create and export cpu_smt_possible()

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@...hat.com>
---
 include/linux/cpu.h |  2 ++
 kernel/cpu.c        | 11 +++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index fcb1386bb0d4..6d48fc456d58 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -201,12 +201,14 @@ 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);
 extern int cpuhp_smt_enable(void);
 extern int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval);
 #else
 # define cpu_smt_control		(CPU_SMT_NOT_IMPLEMENTED)
 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; }
 static inline int cpuhp_smt_enable(void) { return 0; }
 static inline int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) { return 0; }
 #endif
diff --git a/kernel/cpu.c b/kernel/cpu.c
index e84c0873559e..2f8c2631e641 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -389,8 +389,7 @@ enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
 
 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) {
@@ -435,6 +434,14 @@ static inline bool cpu_smt_allowed(unsigned int cpu)
 	 */
 	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
-- 
2.20.1