[tip: x86/entry] x86/entry/64: Avoid pointless code when CONTEXT_TRACKING=n

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     cd19bff6935f29ad06513562b59ebdfe2d34eae4
Gitweb:        https://git.kernel.org/tip/cd19bff6935f29ad06513562b59ebdfe2d34eae4
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Tue, 25 Feb 2020 23:16:08 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Fri, 15 May 2020 20:03:04 +02:00

x86/entry/64: Avoid pointless code when CONTEXT_TRACKING=n

GAS cannot optimize out the test and conditional jump when context tracking
is disabled and CALL_enter_from_user_mode is an empty macro.

Wrap it in #ifdeffery. Will go away once all this is moved to C.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Acked-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200505134058.955968069@xxxxxxxxxxxxx


---
 arch/x86/entry/entry_64.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 7d40d10..f84b0f6 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -889,12 +889,14 @@ apicinterrupt IRQ_WORK_VECTOR			irq_work_interrupt		smp_irq_work_interrupt
 	TRACE_IRQS_OFF
 	.endif
 
+#ifdef CONFIG_CONTEXT_TRACKING
 	.if \paranoid == 0
 	testb	$3, CS(%rsp)
 	jz	.Lfrom_kernel_no_context_tracking_\@
 	CALL_enter_from_user_mode
 .Lfrom_kernel_no_context_tracking_\@:
 	.endif
+#endif
 
 	movq	%rsp, %rdi			/* pt_regs pointer */