x86/entry: Define 'cpu_current_top_of_stack' for 64-bit code

32-bit code has PER_CPU_VAR(cpu_current_top_of_stack).
64-bit code uses somewhat more obscure: PER_CPU_VAR(cpu_tss + TSS_sp0).

Define the 'cpu_current_top_of_stack' macro on CONFIG_X86_64
as well so that the PER_CPU_VAR(cpu_current_top_of_stack)
expression can be used in both 32-bit and 64-bit code.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1429889495-27850-3-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 1b1330c..63450a5 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -113,7 +113,7 @@
 	 * it is too small to ever cause noticeable irq latency.
 	 */
 	SWAPGS_UNSAFE_STACK
-	movq	PER_CPU_VAR(cpu_tss + TSS_sp0), %rsp
+	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 	ENABLE_INTERRUPTS(CLBR_NONE)
 
 	/* Zero-extending 32-bit regs, do not remove */
@@ -346,7 +346,7 @@
 	SWAPGS_UNSAFE_STACK
 	movl	%esp,%r8d
 	CFI_REGISTER	rsp,r8
-	movq	PER_CPU_VAR(cpu_tss + TSS_sp0),%rsp
+	movq	PER_CPU_VAR(cpu_current_top_of_stack),%rsp
 	ENABLE_INTERRUPTS(CLBR_NONE)
 
 	/* Zero-extending 32-bit regs, do not remove */