diff options
Diffstat (limited to 'arch/x86/include/asm/mmu_context.h')
| -rw-r--r-- | arch/x86/include/asm/mmu_context.h | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 40269a2bf6f9..4b75d591eb5e 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -130,7 +130,25 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm, static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long start, unsigned long end) { - mpx_notify_unmap(mm, vma, start, end); + /* + * mpx_notify_unmap() goes and reads a rarely-hot + * cacheline in the mm_struct. That can be expensive + * enough to be seen in profiles. + * + * The mpx_notify_unmap() call and its contents have been + * observed to affect munmap() performance on hardware + * where MPX is not present. + * + * The unlikely() optimizes for the fast case: no MPX + * in the CPU, or no MPX use in the process. Even if + * we get this wrong (in the unlikely event that MPX + * is widely enabled on some system) the overhead of + * MPX itself (reading bounds tables) is expected to + * overwhelm the overhead of getting this unlikely() + * consistently wrong. + */ + if (unlikely(cpu_feature_enabled(X86_FEATURE_MPX))) + mpx_notify_unmap(mm, vma, start, end); } #endif /* _ASM_X86_MMU_CONTEXT_H */ |