Commit 478dc89c authored Nov 12, 2015 by Andy Lutomirski Committed by Ingo Molnar Nov 24, 2015

x86/entry/64: Bypass enter_from_user_mode on non-context-tracking boots



On CONFIG_CONTEXT_TRACKING kernels that have context tracking
disabled at runtime (which includes most distro kernels), we
still have the overhead of a call to enter_from_user_mode in
interrupt and exception entries.

If jump labels are available, this uses the jump label
infrastructure to skip the call.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/73ee804fff48cd8c66b65b724f9f728a11a8c686.1447361906.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 2671c3e4

arch/x86/entry/calling.h

+15 −0

Original line number	Diff line number	Diff line
		#include <linux/jump_label.h>

		/*

		x86 function call convention, 64-bit:
		@@ -232,3 +234,16 @@ For 32-bit we have the following conventions - kernel is built with

		#endif /* CONFIG_X86_64 */

		/*
		* This does 'call enter_from_user_mode' unless we can avoid it based on
		* kernel config or using the static jump infrastructure.
		*/
		.macro CALL_enter_from_user_mode
		#ifdef CONFIG_CONTEXT_TRACKING
		#ifdef HAVE_JUMP_LABEL
		STATIC_JUMP_IF_FALSE .Lafter_call_\@, context_tracking_enabled, def=0
		#endif
		call enter_from_user_mode
		.Lafter_call_\@:
		#endif
		.endm

arch/x86/entry/entry_64.S

+2 −6

Original line number	Diff line number	Diff line
		@@ -520,9 +520,7 @@ END(irq_entries_start)
		*/
		TRACE_IRQS_OFF

		#ifdef CONFIG_CONTEXT_TRACKING
		call enter_from_user_mode
		#endif
		CALL_enter_from_user_mode

		1:
		/*
		@@ -1066,9 +1064,7 @@ ENTRY(error_entry)
		* (which can take locks).
		*/
		TRACE_IRQS_OFF
		#ifdef CONFIG_CONTEXT_TRACKING
		call enter_from_user_mode
		#endif
		CALL_enter_from_user_mode
		ret

		.Lerror_entry_done:

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