[PATCH v2] x86: hyperv: fix build in !CONFIG_KEXEC_CORE case

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Recent changes in Hyper-V driver ("Drivers: hv: vmbus: add special crash
handler") broke the build when CONFIG_KEXEC_CORE is not set:

arch/x86/built-in.o: In function `hv_machine_crash_shutdown':
arch/x86/kernel/cpu/mshyperv.c:112: undefined reference to `native_machine_crash_shutdown'

Decorate all kexec related code with #ifdef CONFIG_KEXEC_CORE.

Reported-by: Jim Davis <jim.epost@gmail.com>
Reported-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Previously I tried solving the issue by defining native_machine_crash_shutdown
in !CONFIG_KEXEC_CORE case: https://lkml.org/lkml/2015/8/11/417. This was to
avoid having #ifdefs in C code [Greg KH]. Such approach, however, raised a
question on bloating kernel with unneeded stuff [Ingo Molnar].
---
 arch/x86/kernel/cpu/mshyperv.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 381c8b9..6cec20a 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -98,6 +98,7 @@ void hv_remove_crash_handler(void)
 EXPORT_SYMBOL_GPL(hv_remove_crash_handler);
 #endif
 
+#ifdef CONFIG_KEXEC_CORE
 static void hv_machine_shutdown(void)
 {
 	if (kexec_in_progress && hv_kexec_handler)
@@ -111,7 +112,7 @@ static void hv_machine_crash_shutdown(struct pt_regs *regs)
 		hv_crash_handler(regs);
 	native_machine_crash_shutdown(regs);
 }
-
+#endif
 
 static uint32_t  __init ms_hyperv_platform(void)
 {
@@ -186,8 +187,10 @@ static void __init ms_hyperv_init_platform(void)
 	no_timer_check = 1;
 #endif
 
+#ifdef CONFIG_KEXEC_CORE
 	machine_ops.shutdown = hv_machine_shutdown;
 	machine_ops.crash_shutdown = hv_machine_crash_shutdown;
+#endif
 	mark_tsc_unstable("running on Hyper-V");
 }
 
-- 
2.4.3