Re: [PATCH v6 3/5] lazy tlb: shoot lazies, non-refcounting lazy tlb mm reference handling scheme

[Nadav Amit]

> On Jan 18, 2023, at 12:00 AM, Nicholas Piggin <npig...@gmail.com> wrote:
> 
> +static void do_shoot_lazy_tlb(void *arg)
> +{
> +     struct mm_struct *mm = arg;
> +
> +     if (current->active_mm == mm) {
> +             WARN_ON_ONCE(current->mm);
> +             current->active_mm = &init_mm;
> +             switch_mm(mm, &init_mm, current);
> +     }
> +}

I might be out of touch - doesn’t a flush already take place when we free
the page-tables, at least on common cases on x86?

IIUC exit_mmap() would free page-tables, and whenever page-tables are
freed, on x86, we do shootdown regardless to whether the target CPU TLB state
marks is_lazy. Then, flush_tlb_func() should call switch_mm_irqs_off() and
everything should be fine, no?

[ I understand you care about powerpc, just wondering on the effect on x86 ]