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

[Dev Jain <dev.jain@arm.com>]

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;
 	}
-- 
2.43.0