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Commit 39b48e57 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/entry: Split and inline prepare_exit_to_usermode() 



GCC is unable to properly optimize functions that have a very
short likely case and a longer and register-heavier cold part --
it fails to sink all of the register saving and stack frame
setup code into the unlikely part.

Help it out with prepare_exit_to_usermode() by splitting it into
two parts and inline the hot part.

Saves 6-8 cycles for compat syscalls.

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
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: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/9fc53eda4a5b924070952f12fa4ae3e477640a07.1444091585.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent dd636071

arch/x86/entry/common.c

+28 −15
Original line number Diff line number Diff line
@@ -218,14 +218,12 @@ long syscall_trace_enter(struct pt_regs *regs) 
		return syscall_trace_enter_phase2(regs, arch, phase1_result);

}



/* Called with IRQs disabled. */

__visible void prepare_exit_to_usermode(struct pt_regs *regs)

{

	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))

		local_irq_disable();



	lockdep_sys_exit();

#define EXIT_TO_USERMODE_LOOP_FLAGS				\

	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\

	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)



static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)

{

	/*

	 * In order to return to user mode, we need to have IRQs off with

	 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
@@ -235,14 +233,6 @@ __visible void prepare_exit_to_usermode(struct pt_regs *regs) 
	 * work to clear some of the flags can sleep.

	 */

	while (true) {

		u32 cached_flags =

			READ_ONCE(pt_regs_to_thread_info(regs)->flags);



		if (!(cached_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME |

				      _TIF_UPROBE | _TIF_NEED_RESCHED |

				      _TIF_USER_RETURN_NOTIFY)))

			break;



		/* We have work to do. */

		local_irq_enable();
@@ -266,8 +256,31 @@ __visible void prepare_exit_to_usermode(struct pt_regs *regs) 


		/* Disable IRQs and retry */

		local_irq_disable();



		cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);



		if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))

			break;



	}

}



/* Called with IRQs disabled. */

__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)

{

	u32 cached_flags;



	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))

		local_irq_disable();



	lockdep_sys_exit();



	cached_flags =

		READ_ONCE(pt_regs_to_thread_info(regs)->flags);



	if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))

		exit_to_usermode_loop(regs, cached_flags);



	user_enter();

}