linux-kernel - [PATCH v3 6/7] x86: paravirt: shut up unused native_pv_lock

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Date:   Thu,  3 Aug 2023 10:26:18 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH v3 6/7] x86: paravirt: shut up unused native_pv_lock_init() function warning

From: Arnd Bergmann <arnd@...db.de>

The native_pv_lock_init function is only used in SMP configurations
and declared in asm/qspinlock.h, which is not used in UP kernels,
but the function is still defined for both, which causes a warning:

    arch/x86/kernel/paravirt.c:76:13: error: no previous prototype for 'native_pv_lock_init' [-Werror=missing-prototypes]

Move the declaration to asm/paravirt.h so it is visible even
with CONFIG_SMP but short-circuit the definition to turn it
into an empty function.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
v3: new patch to avoid adding another #ifdef to paravirt.c
---
 arch/x86/include/asm/paravirt.h  | 7 +++++++
 arch/x86/include/asm/qspinlock.h | 7 +------
 arch/x86/kernel/paravirt.c       | 3 ++-
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index b49778664d2be..6c8ff12140aea 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -739,6 +739,7 @@ static __always_inline unsigned long arch_local_irq_save(void)
 	     ".popsection")
 
 extern void default_banner(void);
+void native_pv_lock_init(void) __init;
 
 #else  /* __ASSEMBLY__ */
 
@@ -778,6 +779,12 @@ extern void default_banner(void);
 #endif /* __ASSEMBLY__ */
 #else  /* CONFIG_PARAVIRT */
 # define default_banner x86_init_noop
+
+#ifndef __ASSEMBLY__
+static inline void native_pv_lock_init(void)
+{
+}
+#endif
 #endif /* !CONFIG_PARAVIRT */
 
 #ifndef __ASSEMBLY__
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index d87451df480bd..cde8357bb226d 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -74,8 +74,6 @@ static inline bool vcpu_is_preempted(long cpu)
  */
 DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);
 
-void native_pv_lock_init(void) __init;
-
 /*
  * Shortcut for the queued_spin_lock_slowpath() function that allows
  * virt to hijack it.
@@ -103,10 +101,7 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
 
 	return true;
 }
-#else
-static inline void native_pv_lock_init(void)
-{
-}
+
 #endif /* CONFIG_PARAVIRT */
 
 #include <asm-generic/qspinlock.h>
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 89842bb7ec9cc..066fc19d2568e 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -75,7 +75,8 @@ DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
 
 void __init native_pv_lock_init(void)
 {
-	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
+	if (IS_ENABLED(CONFIG_PARAVIRT_SPINLOCKS) &&
+	    !boot_cpu_has(X86_FEATURE_HYPERVISOR))
 		static_branch_disable(&virt_spin_lock_key);
 }
 
-- 
2.39.2