From: Xin Li (Intel) Date: Thu, 22 Aug 2024 07:39:04 +0000 (-0700) Subject: x86/entry: Test ti_work for zero before processing individual bits X-Git-Tag: v6.12-rc1~179^2~2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0dfac6f267fa091aa348c6a6742b463c9e7c98e3;p=thirdparty%2Fkernel%2Flinux.git 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: H. Peter Anvin (Intel) Signed-off-by: Xin Li (Intel) Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20240822073906.2176342-2-xin@zytor.com --- diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h index fb2809b20b0ac..db970828f3856 100644 --- a/arch/x86/include/asm/entry-common.h +++ b/arch/x86/include/asm/entry-common.h @@ -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 /*