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

tip-bot2 for Thomas Gleixner
2020-05-19T19:59:47Z

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@linutronix.de>
AuthorDate: Tue, 25 Feb 2020 23:16:08 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
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@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

---
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 */