Re: [RFC 03/10] x86/mm: Make the batched unmap TLB flush API more generic

Dave Hansen
2017-05-08T15:35:00Z

On 05/07/2017 05:38 AM, Andy Lutomirski wrote:
> diff --git a/mm/rmap.c b/mm/rmap.c
> index f6838015810f..2e568c82f477 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -579,25 +579,12 @@ void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
> void try_to_unmap_flush(void)
> {
> struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
> - int cpu;
>
> if (!tlb_ubc->flush_required)
> return;
>
> - cpu = get_cpu();
> -
> - if (cpumask_test_cpu(cpu, &tlb_ubc->cpumask)) {
> - count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
> - local_flush_tlb();
> - trace_tlb_flush(TLB_LOCAL_SHOOTDOWN, TLB_FLUSH_ALL);
> - }
> -
> - if (cpumask_any_but(&tlb_ubc->cpumask, cpu) < nr_cpu_ids)
> - flush_tlb_others(&tlb_ubc->cpumask, NULL, 0, TLB_FLUSH_ALL);
> - cpumask_clear(&tlb_ubc->cpumask);
> tlb_ubc->flush_required = false;
> tlb_ubc->writable = false;
> - put_cpu();
> }
>
> /* Flush iff there are potentially writable TLB entries that can race with IO */
> @@ -613,7 +600,7 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
> {
> struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
>
> - cpumask_or(&tlb_ubc->cpumask, &tlb_ubc->cpumask, mm_cpumask(mm));
> + arch_tlbbatch_add_mm(&tlb_ubc->arch, mm);
> tlb_ubc->flush_required = true;
>
> /*

Looking at this patch in isolation, how can this be safe? It removes
TLB flushes from the generic code. Do other patches in the series fix
this up?