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

David Hildenbrand (Arm)
2026-04-27T09:03:00Z

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@linux.ibm.com>
> ---
> 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