Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID
From: Peter Zijlstra
Date: Wed Jul 05 2017 - 13:02:41 EST
On Wed, Jul 05, 2017 at 09:04:39AM -0700, Andy Lutomirski wrote:
> On Wed, Jul 5, 2017 at 5:18 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Thu, Jun 29, 2017 at 08:53:22AM -0700, Andy Lutomirski wrote:
> >> @@ -104,18 +140,20 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
> >> /* Resume remote flushes and then read tlb_gen. */
> >> cpumask_set_cpu(cpu, mm_cpumask(next));
> > Barriers should have a comment... what is being ordered here against
> > what?
> How's this comment?
> * Resume remote flushes and then read tlb_gen. We need to do
> * it in this order: any inc_mm_tlb_gen() caller that writes a
> * larger tlb_gen than we read here must see our cpu set in
> * mm_cpumask() so that it will know to flush us. The barrier
> * here synchronizes with inc_mm_tlb_gen().
Slightly confusing, you mean this, right?
cpumask_set_cpu(cpu, mm_cpumask()); inc_mm_tlb_gen();
next_tlb_gen = atomic64_read(&next->context.tlb_gen); flush_tlb_others(mm_cpumask());
which seems to make sense.