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

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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) <hpa@zytor.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240822073906.2176342-2-xin@zytor.com
This commit is contained in:
Xin Li (Intel) 2024-08-22 00:39:04 -07:00 committed by Thomas Gleixner
parent 723edbd2ca
commit 0dfac6f267
1 changed files with 8 additions and 2 deletions
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10
arch/x86/include/asm/entry-common.h
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@ -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
/*