Re: [PATCH v4 06/12] mm: introduce generic lazy_mmu helpers

["David Hildenbrand (Red Hat)" <davidhildenbrandkernel@gmail.com>]

>>   #ifndef pte_batch_hint
>> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
>> index 5d2a876035d6..c49b029d3593 100644
>> --- a/mm/kasan/shadow.c
>> +++ b/mm/kasan/shadow.c
>> @@ -305,7 +305,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>>   	pte_t pte;
>>   	int index;
>>   
>> -	arch_leave_lazy_mmu_mode();
>> +	lazy_mmu_mode_pause();
> 
> I wonder if there really are use cases that *require* pause/resume? I think
> these kasan cases could be correctly implemented using a new nest level instead?
> Are there cases where the effects really need to be immediate or do the effects
> just need to be visible when you get to where the resume is?
> 
> If the latter, that could just be turned into a nested disable (e.g. a flush).
> In this case, there is only 1 PTE write so no benefit, but I wonder if other
> cases may have more PTE writes that could then still be batched. It would be
> nice to simplify the API by removing pause/resume if we can?

It has clear semantics, clearer than some nest-disable IMHO.

Maybe you can elaborate how you would change ("simplify") the API in 
that regard? What would the API look like?