Re: [PATCH 4/5] mm/page_vma_mapped: use huge_ptep_get() for hugetlb

[Lance Yang <lance.yang@linux.dev>]

On Thu, Jun 25, 2026 at 11:29:53AM +0000, Dev Jain wrote:
>check_pte() is the final validation step in page_vma_mapped_walk().
>It reads pvmw->pte with ptep_get() to decide whether the entry maps
>the PFN range being walked. For hugetlb VMAs, that pointer refers
>to a hugetlb entry.
>
>On arches which provide their own huge_ptep_get() to dereference a huge
>pte pointer, accessing via ptep_get() would cause pte_pfn(),
>pte_present() etc to misbehave.
>
>It is not clear whether this has a trivially visible effect to userspace.
>
>Use huge_ptep_get() to dereference a huge pte pointer.
>
>Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()")
>Cc: stable@vger.kernel.org
>Signed-off-by: Dev Jain <dev.jain@arm.com>
>---
> mm/page_vma_mapped.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
>diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
>index 2ccbabfb2cc17..18e1d341f463c 100644
>--- a/mm/page_vma_mapped.c
>+++ b/mm/page_vma_mapped.c
>@@ -107,7 +107,13 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
> static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)

Just one ordering thing: should this patch come first?

Patches #01-#03 only reach the new huge_ptep_get() after
page_vma_mapped_walk() succeeds. But before this patch, hugetlb sill
goes through check_pte() (still using ptep_get()).

> {
> 	unsigned long pfn;
>-	pte_t ptent = ptep_get(pvmw->pte);
>+	pte_t ptent;
>+
>+	if (is_vm_hugetlb_page(pvmw->vma))
>+		ptent = huge_ptep_get(pvmw->vma->vm_mm, pvmw->address,
>+				      pvmw->pte);
>+	else
>+		ptent = ptep_get(pvmw->pte);
> 
> 	if (pvmw->flags & PVMW_MIGRATION) {
> 		const softleaf_t entry = softleaf_from_pte(ptent);
>-- 
>2.43.0
>
>