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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>
This commit is contained in:
Andy Lutomirski 2015-11-12 12:59:04 -08:00 committed by Ingo Molnar
parent 2671c3e4fe
commit 478dc89cf3
2 changed files with 17 additions and 6 deletions
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15
arch/x86/entry/calling.h
View File

@ -1,3 +1,5 @@
#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

8
arch/x86/entry/entry_64.S
View File

@ -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: