Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID
From: Andy Lutomirski
Date: Wed Jul 05 2017 - 12:05:06 EST
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
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().