Re: [PATCH] mm/page_vma_mapped_walk: add missing pgtable entry accessors

[David Hildenbrand (Arm)]

On 4/27/26 07:20, Alexander Gordeev wrote:
> Convert pgtable direct entry dereferences to the corresponding
> pXdp_get() accessors. Use ptep_get_lockless() variant for PTE
> reads when no lock is taken.
> 
> Signed-off-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
> ---
>  mm/page_vma_mapped.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index b38a1d00c971..a4520bb10d2a 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -41,7 +41,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
>  	if (!pvmw->pte)
>  		return false;
>  
> -	ptent = ptep_get(pvmw->pte);
> +	ptent = ptep_get_lockless(pvmw->pte);
>  
>  	if (pte_none(ptent)) {
>  		return false;
> @@ -219,17 +219,17 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
>  restart:
>  	do {
>  		pgd = pgd_offset(mm, pvmw->address);
> -		if (!pgd_present(*pgd)) {
> +		if (!pgd_present(pgdp_get(pgd))) {
>  			step_forward(pvmw, PGDIR_SIZE);
>  			continue;
>  		}
>  		p4d = p4d_offset(pgd, pvmw->address);
> -		if (!p4d_present(*p4d)) {
> +		if (!p4d_present(p4dp_get(p4d))) {
>  			step_forward(pvmw, P4D_SIZE);
>  			continue;
>  		}
>  		pud = pud_offset(p4d, pvmw->address);
> -		if (!pud_present(*pud)) {
> +		if (!pud_present(pudp_get(pud))) {
>  			step_forward(pvmw, PUD_SIZE);
>  			continue;

Wasn't there a problem with folded page tables, where we would no longer be able
to optimize out the folded page table accesses?

I thought we discussed ways to resolve that. Let me dig ...

-- 
Cheers,

David