Re: [PATCH 7.2 v10 2/2] x86/tlb: skip redundant sync IPIs for native TLB flush

Peter Zijlstra
2026-04-24T15:13:05Z

On Fri, Apr 24, 2026 at 02:25:28PM +0800, Lance Yang wrote:
> diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
> index cfcb60468b01..2cf1eeaffd6f 100644
> --- a/arch/x86/hyperv/mmu.c
> +++ b/arch/x86/hyperv/mmu.c
> @@ -63,7 +63,7 @@ static void hyperv_flush_tlb_multi(const struct cpumask *cpus,
> struct hv_tlb_flush *flush;
> u64 status;
> unsigned long flags;
> - bool do_lazy = !info->freed_tables;
> + bool do_lazy = !info->wake_lazy_cpus;
>
> trace_hyperv_mmu_flush_tlb_multi(cpus, info);
>
> @@ -198,7 +198,7 @@ static u64 hyperv_flush_tlb_others_ex(const struct cpumask *cpus,
>
> flush->hv_vp_set.format = HV_GENERIC_SET_SPARSE_4K;
> nr_bank = cpumask_to_vpset_skip(&flush->hv_vp_set, cpus,
> - info->freed_tables ? NULL : cpu_is_lazy);
> + info->wake_lazy_cpus ? NULL : cpu_is_lazy);
> if (nr_bank < 0)
> return HV_STATUS_INVALID_PARAMETER;
>
> diff --git a/arch/x86/include/asm/tlb.h b/arch/x86/include/asm/tlb.h
> index 866ea78ba156..fb256fd95f95 100644
> --- a/arch/x86/include/asm/tlb.h
> +++ b/arch/x86/include/asm/tlb.h

> static inline void tlb_flush(struct mmu_gather *tlb)
> {
> unsigned long start = 0UL, end = TLB_FLUSH_ALL;
> unsigned int stride_shift = tlb_get_unmap_shift(tlb);
>
> + /*
> + * Both freed_tables and unshared_tables must wake lazy-TLB CPUs, so
> + * they receive IPIs before reusing or freeing page tables, allowing
> + * us to safely implement tlb_table_flush_implies_ipi_broadcast().
> + */
> + bool wake_lazy_cpus = tlb->freed_tables || tlb->unshared_tables;
> +
> if (!tlb->fullmm && !tlb->need_flush_all) {
> start = tlb->start;
> end = tlb->end;
> }
>
> - flush_tlb_mm_range(tlb->mm, start, end, stride_shift, tlb->freed_tables);
> + flush_tlb_mm_range(tlb->mm, start, end, stride_shift, wake_lazy_cpus);
> }
>
> static inline void invlpg(unsigned long addr)
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index 5a3cdc439e38..39b9454781c3 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -225,7 +227,7 @@ struct flush_tlb_info {
> u64 new_tlb_gen;
> unsigned int initiating_cpu;
> u8 stride_shift;
> - u8 freed_tables;
> + u8 wake_lazy_cpus;
> u8 trim_cpumask;
> };
>
> @@ -315,7 +317,7 @@ static inline bool mm_in_asid_transition(struct mm_struct *mm) { return false; }
> extern void flush_tlb_all(void);
> extern void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
> unsigned long end, unsigned int stride_shift,
> - bool freed_tables);
> + bool wake_lazy_cpus);
> extern void flush_tlb_kernel_range(unsigned long start, unsigned long end);
>
> static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a)

> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 621e09d049cb..3ce254a3982c 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -1360,16 +1362,16 @@ STATIC_NOPV void native_flush_tlb_multi(const struct cpumask *cpumask,
> (info->end - info->start) >> PAGE_SHIFT);
>
> /*
> - * If no page tables were freed, we can skip sending IPIs to
> - * CPUs in lazy TLB mode. They will flush the CPU themselves
> - * at the next context switch.
> + * If lazy-TLB CPUs do not need to be woken, we can skip sending
> + * IPIs to them. They will flush themselves at the next context
> + * switch.
> *
> - * However, if page tables are getting freed, we need to send the
> - * IPI everywhere, to prevent CPUs in lazy TLB mode from tripping
> - * up on the new contents of what used to be page tables, while
> - * doing a speculative memory access.
> + * However, if page tables are getting freed or unshared, we need
> + * to send the IPI everywhere, to prevent CPUs in lazy TLB mode
> + * from tripping up on the new contents of what used to be page
> + * tables, while doing a speculative memory access.
> */
> - if (info->freed_tables || mm_in_asid_transition(info->mm))
> + if (info->wake_lazy_cpus || mm_in_asid_transition(info->mm))
> on_each_cpu_mask(cpumask, flush_tlb_func, (void *)info, true);
> else
> on_each_cpu_cond_mask(should_flush_tlb, flush_tlb_func,
> @@ -1402,7 +1404,7 @@ static DEFINE_PER_CPU(unsigned int, flush_tlb_info_idx);
>
> static struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm,
> unsigned long start, unsigned long end,
> - unsigned int stride_shift, bool freed_tables,
> + unsigned int stride_shift, bool wake_lazy_cpus,
> u64 new_tlb_gen)
> {
> struct flush_tlb_info *info = this_cpu_ptr(&flush_tlb_info);
> @@ -1429,7 +1431,7 @@ static struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm,
> info->end = end;
> info->mm = mm;
> info->stride_shift = stride_shift;
> - info->freed_tables = freed_tables;
> + info->wake_lazy_cpus = wake_lazy_cpus;
> info->new_tlb_gen = new_tlb_gen;
> info->initiating_cpu = smp_processor_id();
> info->trim_cpumask = 0;
> @@ -1448,7 +1450,7 @@ static void put_flush_tlb_info(void)
>
> void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
> unsigned long end, unsigned int stride_shift,
> - bool freed_tables)
> + bool wake_lazy_cpus)
> {
> struct flush_tlb_info *info;
> int cpu = get_cpu();
> @@ -1457,7 +1459,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
> /* This is also a barrier that synchronizes with switch_mm(). */
> new_tlb_gen = inc_mm_tlb_gen(mm);
>
> - info = get_flush_tlb_info(mm, start, end, stride_shift, freed_tables,
> + info = get_flush_tlb_info(mm, start, end, stride_shift, wake_lazy_cpus,
> new_tlb_gen);
>
> /*

This whole s/freed_tables/wake_lazy_cpus/ rename should probably be its
own patch, as should that include unshare_tables thing be.

That seems like unrelated changes.