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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: Andy 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2015-10-05 17:48:23 -07:00 committed by Ingo Molnar
parent dd636071c3
commit 39b48e575e
1 changed files with 28 additions and 15 deletions
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43
arch/x86/entry/common.c
View File

@ -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)
#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)
{
if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
local_irq_disable();
lockdep_sys_exit();
/*
* 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();
@ -266,7 +256,30 @@ __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();
}