Re: [PATCH v2 1/6] arm64: make huge_ptep_get handled unaligned addresses

["David Hildenbrand (Arm)" <david@kernel.org>]

On 7/2/26 07:13, Dev Jain wrote:
> huge_ptep_get() can be handed a virtual address pointing to the middle of
> a contpmd/contpte mapped hugetlb folio (examples of callers are
> pagemap_hugetlb_range, page_mapped_in_vma).
> 
> The arm64 helper rewalks the pgtables in find_num_contig to answer whether
> the huge pte we have maps a contpmd or a contpte hugetlb folio, and
> returns CONT_PMDS or CONT_PTES, so that it can collect a/d bits over the
> contiguous ptes. We can falsely return CONT_PTES instead of CONT_PMDS
> if the addr is not aligned.
> 
> Fix this by aligning the pmdp pointer down to a contpmd base before
> checking equality with the passed huge pte pointer, to correctly answer
> whether the huge pte is the base of a contpmd block.
> 
> Fixes: 29cb80519689 ("arm64: hugetlb: Cleanup huge_pte size discovery mechanisms")
> Cc: stable@vger.kernel.org
> Signed-off-by: Dev Jain <dev.jain@arm.com>
> ---
>  arch/arm64/mm/hugetlbpage.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index 30772a909aea3..8e799c1fe0aa6 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -87,7 +87,7 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr,
>  	p4dp = p4d_offset(pgdp, addr);
>  	pudp = pud_offset(p4dp, addr);
>  	pmdp = pmd_offset(pudp, addr);
> -	if ((pte_t *)pmdp == ptep) {
> +	if ((pte_t *)PTR_ALIGN_DOWN(pmdp, sizeof(*pmdp) * CONT_PMDS) == ptep) {
>  		*pgsize = PMD_SIZE;
>  		return CONT_PMDS;
>  	}


Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David