x86: provide 64-bit with a load_sp0 function.

Paravirt guests need to inform the underlying hypervisor whenever the sp0
tss field changes. i386 already has such a function, and we use it for
x86_64 too. There's an unnecessary (for 64-bit) msr handling part in the original
version, and it is placed around an ifdef. Making no more sense in
processor_32.h, it is moved to the common header

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index af56104..e3a3610 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -639,7 +639,7 @@
 	/*
 	 * Reload esp0, LDT and the page table pointer:
 	 */
-	tss->x86_tss.sp0 = next->sp0;
+	load_sp0(tss, next);
 
 	/* 
 	 * Switch DS and ES.
diff --git a/arch/x86/kernel/smpboot_64.c b/arch/x86/kernel/smpboot_64.c
index 2ea02a7..5bd42ce 100644
--- a/arch/x86/kernel/smpboot_64.c
+++ b/arch/x86/kernel/smpboot_64.c
@@ -614,7 +614,7 @@
 	start_rip = setup_trampoline();
 
 	init_rsp = c_idle.idle->thread.sp;
-	per_cpu(init_tss, cpu).x86_tss.sp0 = init_rsp;
+	load_sp0(&per_cpu(init_tss, cpu), &c_idle.idle->thread);
 	initial_code = start_secondary;
 	clear_tsk_thread_flag(c_idle.idle, TIF_FORK);