Re: [PATCH v5 8/9] mm: multi-gen LRU: Have secondary MMUs participate in aging

[Sean Christopherson <seanjc@google.com>]

On Tue, Jun 11, 2024, James Houghton wrote:
> diff --git a/mm/rmap.c b/mm/rmap.c
> index e8fc5ecb59b2..24a3ff639919 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -870,13 +870,10 @@ static bool folio_referenced_one(struct folio *folio,
>  			continue;
>  		}
>  
> -		if (pvmw.pte) {
> -			if (lru_gen_enabled() &&
> -			    pte_young(ptep_get(pvmw.pte))) {
> -				lru_gen_look_around(&pvmw);
> +		if (lru_gen_enabled() && pvmw.pte) {
> +			if (lru_gen_look_around(&pvmw))
>  				referenced++;
> -			}
> -
> +		} else if (pvmw.pte) {
>  			if (ptep_clear_flush_young_notify(vma, address,
>  						pvmw.pte))
>  				referenced++;

Random question not really related to KVM/secondary MMU participation.  AFAICT,
the MGLRU approach doesn't flush TLBs after aging pages.  How does MGLRU mitigate
false negatives on pxx_young() due to the CPU not setting Accessed bits because
of stale TLB entries?