diff options
Diffstat (limited to 'arch/x86/mm/tlb.c')
| -rw-r--r-- | arch/x86/mm/tlb.c | 224 |
1 files changed, 165 insertions, 59 deletions
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 6eb1f34c3c85..752dbf4e0e50 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -7,6 +7,7 @@ #include <linux/export.h> #include <linux/cpu.h> #include <linux/debugfs.h> +#include <linux/gfp.h> #include <asm/tlbflush.h> #include <asm/mmu_context.h> @@ -35,7 +36,7 @@ * necessary invalidation by clearing out the 'ctx_id' which * forces a TLB flush when the context is loaded. */ -void clear_asid_other(void) +static void clear_asid_other(void) { u16 asid; @@ -185,8 +186,11 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, { struct mm_struct *real_prev = this_cpu_read(cpu_tlbstate.loaded_mm); u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid); + bool was_lazy = this_cpu_read(cpu_tlbstate.is_lazy); unsigned cpu = smp_processor_id(); u64 next_tlb_gen; + bool need_flush; + u16 new_asid; /* * NB: The scheduler will call us with prev == next when switching @@ -240,20 +244,41 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, next->context.ctx_id); /* - * We don't currently support having a real mm loaded without - * our cpu set in mm_cpumask(). We have all the bookkeeping - * in place to figure out whether we would need to flush - * if our cpu were cleared in mm_cpumask(), but we don't - * currently use it. + * Even in lazy TLB mode, the CPU should stay set in the + * mm_cpumask. The TLB shootdown code can figure out from + * from cpu_tlbstate.is_lazy whether or not to send an IPI. */ if (WARN_ON_ONCE(real_prev != &init_mm && !cpumask_test_cpu(cpu, mm_cpumask(next)))) cpumask_set_cpu(cpu, mm_cpumask(next)); - return; + /* + * If the CPU is not in lazy TLB mode, we are just switching + * from one thread in a process to another thread in the same + * process. No TLB flush required. + */ + if (!was_lazy) + return; + + /* + * Read the tlb_gen to check whether a flush is needed. + * If the TLB is up to date, just use it. + * The barrier synchronizes with the tlb_gen increment in + * the TLB shootdown code. + */ + smp_mb(); + next_tlb_gen = atomic64_read(&next->context.tlb_gen); + if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) == + next_tlb_gen) + return; + + /* + * TLB contents went out of date while we were in lazy + * mode. Fall through to the TLB switching code below. + */ + new_asid = prev_asid; + need_flush = true; } else { - u16 new_asid; - bool need_flush; u64 last_ctx_id = this_cpu_read(cpu_tlbstate.last_ctx_id); /* @@ -285,53 +310,60 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, sync_current_stack_to_mm(next); } - /* Stop remote flushes for the previous mm */ - VM_WARN_ON_ONCE(!cpumask_test_cpu(cpu, mm_cpumask(real_prev)) && - real_prev != &init_mm); - cpumask_clear_cpu(cpu, mm_cpumask(real_prev)); + /* + * Stop remote flushes for the previous mm. + * Skip kernel threads; we never send init_mm TLB flushing IPIs, + * but the bitmap manipulation can cause cache line contention. + */ + if (real_prev != &init_mm) { + VM_WARN_ON_ONCE(!cpumask_test_cpu(cpu, + mm_cpumask(real_prev))); + cpumask_clear_cpu(cpu, mm_cpumask(real_prev)); + } /* * Start remote flushes and then read tlb_gen. */ - cpumask_set_cpu(cpu, mm_cpumask(next)); + if (next != &init_mm) + cpumask_set_cpu(cpu, mm_cpumask(next)); next_tlb_gen = atomic64_read(&next->context.tlb_gen); choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush); + } - if (need_flush) { - this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id); - this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen); - load_new_mm_cr3(next->pgd, new_asid, true); - - /* - * NB: This gets called via leave_mm() in the idle path - * where RCU functions differently. Tracing normally - * uses RCU, so we need to use the _rcuidle variant. - * - * (There is no good reason for this. The idle code should - * be rearranged to call this before rcu_idle_enter().) - */ - trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); - } else { - /* The new ASID is already up to date. */ - load_new_mm_cr3(next->pgd, new_asid, false); - - /* See above wrt _rcuidle. */ - trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, 0); - } + if (need_flush) { + this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id); + this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen); + load_new_mm_cr3(next->pgd, new_asid, true); /* - * Record last user mm's context id, so we can avoid - * flushing branch buffer with IBPB if we switch back - * to the same user. + * NB: This gets called via leave_mm() in the idle path + * where RCU functions differently. Tracing normally + * uses RCU, so we need to use the _rcuidle variant. + * + * (There is no good reason for this. The idle code should + * be rearranged to call this before rcu_idle_enter().) */ - if (next != &init_mm) - this_cpu_write(cpu_tlbstate.last_ctx_id, next->context.ctx_id); + trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); + } else { + /* The new ASID is already up to date. */ + load_new_mm_cr3(next->pgd, new_asid, false); - this_cpu_write(cpu_tlbstate.loaded_mm, next); - this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid); + /* See above wrt _rcuidle. */ + trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, 0); } + /* + * Record last user mm's context id, so we can avoid + * flushing branch buffer with IBPB if we switch back + * to the same user. + */ + if (next != &init_mm) + this_cpu_write(cpu_tlbstate.last_ctx_id, next->context.ctx_id); + + this_cpu_write(cpu_tlbstate.loaded_mm, next); + this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid); + load_mm_cr4(next); switch_ldt(real_prev, next); } @@ -354,20 +386,7 @@ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm) return; - if (tlb_defer_switch_to_init_mm()) { - /* - * There's a significant optimization that may be possible - * here. We have accurate enough TLB flush tracking that we - * don't need to maintain coherence of TLB per se when we're - * lazy. We do, however, need to maintain coherence of - * paging-structure caches. We could, in principle, leave our - * old mm loaded and only switch to init_mm when - * tlb_remove_page() happens. - */ - this_cpu_write(cpu_tlbstate.is_lazy, true); - } else { - switch_mm(NULL, &init_mm, NULL); - } + this_cpu_write(cpu_tlbstate.is_lazy, true); } /* @@ -454,6 +473,9 @@ static void flush_tlb_func_common(const struct flush_tlb_info *f, * paging-structure cache to avoid speculatively reading * garbage into our TLB. Since switching to init_mm is barely * slower than a minimal flush, just switch to init_mm. + * + * This should be rare, with native_flush_tlb_others skipping + * IPIs to lazy TLB mode CPUs. */ switch_mm_irqs_off(NULL, &init_mm, NULL); return; @@ -560,6 +582,9 @@ static void flush_tlb_func_remote(void *info) void native_flush_tlb_others(const struct cpumask *cpumask, const struct flush_tlb_info *info) { + cpumask_var_t lazymask; + unsigned int cpu; + count_vm_tlb_event(NR_TLB_REMOTE_FLUSH); if (info->end == TLB_FLUSH_ALL) trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL); @@ -583,8 +608,6 @@ void native_flush_tlb_others(const struct cpumask *cpumask, * that UV should be updated so that smp_call_function_many(), * etc, are optimal on UV. */ - unsigned int cpu; - cpu = smp_processor_id(); cpumask = uv_flush_tlb_others(cpumask, info); if (cpumask) @@ -592,8 +615,29 @@ void native_flush_tlb_others(const struct cpumask *cpumask, (void *)info, 1); return; } - smp_call_function_many(cpumask, flush_tlb_func_remote, + + /* + * A temporary cpumask is used in order to skip sending IPIs + * to CPUs in lazy TLB state, while keeping them in mm_cpumask(mm). + * If the allocation fails, simply IPI every CPU in mm_cpumask. + */ + if (!alloc_cpumask_var(&lazymask, GFP_ATOMIC)) { + smp_call_function_many(cpumask, flush_tlb_func_remote, (void *)info, 1); + return; + } + + cpumask_copy(lazymask, cpumask); + + for_each_cpu(cpu, lazymask) { + if (per_cpu(cpu_tlbstate.is_lazy, cpu)) + cpumask_clear_cpu(cpu, lazymask); + } + + smp_call_function_many(lazymask, flush_tlb_func_remote, + (void *)info, 1); + + free_cpumask_var(lazymask); } /* @@ -646,6 +690,68 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, put_cpu(); } +void tlb_flush_remove_tables_local(void *arg) +{ + struct mm_struct *mm = arg; + + if (this_cpu_read(cpu_tlbstate.loaded_mm) == mm && + this_cpu_read(cpu_tlbstate.is_lazy)) { + /* + * We're in lazy mode. We need to at least flush our + * paging-structure cache to avoid speculatively reading + * garbage into our TLB. Since switching to init_mm is barely + * slower than a minimal flush, just switch to init_mm. + */ + switch_mm_irqs_off(NULL, &init_mm, NULL); + } +} + +static void mm_fill_lazy_tlb_cpu_mask(struct mm_struct *mm, + struct cpumask *lazy_cpus) +{ + int cpu; + + for_each_cpu(cpu, mm_cpumask(mm)) { + if (!per_cpu(cpu_tlbstate.is_lazy, cpu)) + cpumask_set_cpu(cpu, lazy_cpus); + } +} + +void tlb_flush_remove_tables(struct mm_struct *mm) +{ + int cpu = get_cpu(); + cpumask_var_t lazy_cpus; + + if (cpumask_any_but(mm_cpumask(mm), cpu) >= nr_cpu_ids) { + put_cpu(); + return; + } + + if (!zalloc_cpumask_var(&lazy_cpus, GFP_ATOMIC)) { + /* + * If the cpumask allocation fails, do a brute force flush + * on all the CPUs that have this mm loaded. + */ + smp_call_function_many(mm_cpumask(mm), + tlb_flush_remove_tables_local, (void *)mm, 1); + put_cpu(); + return; + } + + /* + * CPUs with !is_lazy either received a TLB flush IPI while the user + * pages in this address range were unmapped, or have context switched + * and reloaded %CR3 since then. + * + * Shootdown IPIs at page table freeing time only need to be sent to + * CPUs that may have out of date TLB contents. + */ + mm_fill_lazy_tlb_cpu_mask(mm, lazy_cpus); + smp_call_function_many(lazy_cpus, + tlb_flush_remove_tables_local, (void *)mm, 1); + free_cpumask_var(lazy_cpus); + put_cpu(); +} static void do_flush_tlb_all(void *info) { |