diff options
| -rw-r--r-- | arch/x86/include/asm/mmu_context.h | 26 | ||||
| -rw-r--r-- | arch/x86/mm/tlb.c | 20 |
2 files changed, 28 insertions, 18 deletions
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 1458f530948b..ecfcb6643c9b 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -93,6 +93,32 @@ static inline void load_mm_ldt(struct mm_struct *mm) #else clear_LDT(); #endif +} + +static inline void switch_ldt(struct mm_struct *prev, struct mm_struct *next) +{ +#ifdef CONFIG_MODIFY_LDT_SYSCALL + /* + * Load the LDT if either the old or new mm had an LDT. + * + * An mm will never go from having an LDT to not having an LDT. Two + * mms never share an LDT, so we don't gain anything by checking to + * see whether the LDT changed. There's also no guarantee that + * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL, + * then prev->context.ldt will also be non-NULL. + * + * If we really cared, we could optimize the case where prev == next + * and we're exiting lazy mode. Most of the time, if this happens, + * we don't actually need to reload LDTR, but modify_ldt() is mostly + * used by legacy code and emulators where we don't need this level of + * performance. + * + * This uses | instead of || because it generates better code. + */ + if (unlikely((unsigned long)prev->context.ldt | + (unsigned long)next->context.ldt)) + load_mm_ldt(next); +#endif DEBUG_LOCKS_WARN_ON(preemptible()); } diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 2a5e851f2035..b2485d69f7c2 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -148,25 +148,9 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, real_prev != &init_mm); cpumask_clear_cpu(cpu, mm_cpumask(real_prev)); - /* Load per-mm CR4 state */ + /* Load per-mm CR4 and LDTR state */ load_mm_cr4(next); - -#ifdef CONFIG_MODIFY_LDT_SYSCALL - /* - * Load the LDT, if the LDT is different. - * - * It's possible that prev->context.ldt doesn't match - * the LDT register. This can happen if leave_mm(prev) - * was called and then modify_ldt changed - * prev->context.ldt but suppressed an IPI to this CPU. - * In this case, prev->context.ldt != NULL, because we - * never set context.ldt to NULL while the mm still - * exists. That means that next->context.ldt != - * prev->context.ldt, because mms never share an LDT. - */ - if (unlikely(real_prev->context.ldt != next->context.ldt)) - load_mm_ldt(next); -#endif + switch_ldt(real_prev, next); } /* |