From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 25 Feb 2020 22:16:08 +0000 (+0100)
Subject: x86/entry/64: Avoid pointless code when CONTEXT_TRACKING=n
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=725005897ec4ba07d6227a1ac3121048153eb3ce;p=linux.git

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@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134058.955968069@linutronix.de
---

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 87ffa792bc99e..a15b70ac87b53 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 */