[PATCH v2 1/1] x86/reboot: KVM: Guard nmi_shootdown_cpus_on_restart() with ifdeffery

[Andy Shevchenko]

The nmi_shootdown_cpus_on_restart() in some cases may be not used.
This, in particular, prevents kernel builds with clang, `make W=1`
and CONFIG_WERROR=y:

arch/x86/kernel/reboot.c:957:20: error: unused function 'nmi_shootdown_cpus_on_restart' [-Werror,-Wunused-function]
  957 | static inline void nmi_shootdown_cpus_on_restart(void)
      |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix this by guarging the definitions with the respective KVM ifdeffery.

See also commit 6863f5643dd7 ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
v1: suggested by Dave Hansen
v2: rebased on top of the latest changes in the file
 arch/x86/kernel/reboot.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 615922838c51..67551c474203 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -528,9 +528,9 @@ static inline void kb_wait(void)
 	}
 }
 
+#if IS_ENABLED(CONFIG_KVM_X86)
 static inline void nmi_shootdown_cpus_on_restart(void);
 
-#if IS_ENABLED(CONFIG_KVM_X86)
 /* RCU-protected callback to disable virtualization prior to reboot. */
 static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback;
 
@@ -954,12 +954,6 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 	 */
 }
 
-static inline void nmi_shootdown_cpus_on_restart(void)
-{
-	if (!crash_ipi_issued)
-		nmi_shootdown_cpus(NULL);
-}
-
 /*
  * Check if the crash dumping IPI got issued and if so, call its callback
  * directly. This function is used when we have already been in NMI handler.
@@ -987,9 +981,19 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 	/* No other CPUs to shoot down */
 }
 
-static inline void nmi_shootdown_cpus_on_restart(void) { }
-
 void run_crash_ipi_callback(struct pt_regs *regs)
 {
 }
 #endif
+
+#if IS_ENABLED(CONFIG_KVM_X86)
+#if defined(CONFIG_SMP)
+static inline void nmi_shootdown_cpus_on_restart(void)
+{
+	if (!crash_ipi_issued)
+		nmi_shootdown_cpus(NULL);
+}
+#else /* !CONFIG_SMP */
+static inline void nmi_shootdown_cpus_on_restart(void) { }
+#endif /* !CONFIG_SMP */
+#endif
-- 
2.43.0.rc1.1336.g36b5255a03ac