x86-64, hotplug: Add start_cpu0() entry point to head_64.S

start_cpu0() is defined in head_64.S for 64-bit. The function sets up stack and
jumps to start_secondary() for CPU0 wake up.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1352835171-3958-8-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 94bf9cc2c7ee..980053c4b9cc 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -252,6 +252,22 @@ ENTRY(secondary_startup_64)
         pushq   %rax            # target address in negative space
         lretq
 
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * Boot CPU0 entry point. It's called from play_dead(). Everything has been set
+ * up already except stack. We just set up stack here. Then call
+ * start_secondary().
+ */
+ENTRY(start_cpu0)
+        movq stack_start(%rip),%rsp
+        movq    initial_code(%rip),%rax
+        pushq   $0              # fake return address to stop unwinder
+        pushq   $__KERNEL_CS    # set correct cs
+        pushq   %rax            # target address in negative space
+        lretq
+ENDPROC(start_cpu0)
+#endif
+
         /* SMP bootup changes these two */
         __REFDATA
         .align  8