Commit 0dfac6f2 authored by Xin Li (Intel)'s avatar Xin Li (Intel) Committed by Thomas Gleixner
Browse files

x86/entry: Test ti_work for zero before processing individual bits 



In most cases, ti_work values passed to arch_exit_to_user_mode_prepare()
are zeros, e.g., 99% in kernel build tests.  So an obvious optimization is
to test ti_work for zero before processing individual bits in it.

Omit the optimization when FPU debugging is enabled, otherwise the
FPU consistency check is never executed.

Intel 0day tests did not find a perfermance regression with this change.

Suggested-by: default avatarH. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: default avatarXin Li (Intel) <xin@zytor.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240822073906.2176342-2-xin@zytor.com
parent 723edbd2

arch/x86/include/asm/entry-common.h

+8 −2
Original line number Diff line number Diff line
@@ -44,8 +44,7 @@ static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs) 
}

#define arch_enter_from_user_mode arch_enter_from_user_mode



static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,

						  unsigned long ti_work)

static inline void arch_exit_work(unsigned long ti_work)

{

	if (ti_work & _TIF_USER_RETURN_NOTIFY)

		fire_user_return_notifiers();
@@ -56,6 +55,13 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, 
	fpregs_assert_state_consistent();

	if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))

		switch_fpu_return();

}



static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,

						  unsigned long ti_work)

{

	if (IS_ENABLED(CONFIG_X86_DEBUG_FPU) || unlikely(ti_work))

		arch_exit_work(ti_work);



#ifdef CONFIG_COMPAT

	/*