arm64/hugetlb: implement arm64 specific hugetlb_mask_last_page

The HugeTLB address ranges are linearly scanned during fork, unmap and
remap operations, and the linear scan can skip to the end of range mapped
by the page table page if hitting a non-present entry, which can help to
speed linear scanning of the HugeTLB address ranges.

So hugetlb_mask_last_page() is introduced to help to update the address in
the loop of HugeTLB linear scanning with getting the last huge page mapped
by the associated page table page[1], when a non-present entry is
encountered.

Considering ARM64 specific cont-pte/pmd size HugeTLB, this patch
implemented an ARM64 specific hugetlb_mask_last_page() to help this case.

[1] https://lore.kernel.org/linux-mm/[email protected]/

[[email protected]: fix build]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Baolin Wang <[email protected]>
Signed-off-by: Mike Kravetz <[email protected]>
Acked-by: Muchun Song <[email protected]>
Cc: "Aneesh Kumar K.V" <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: James Houghton <[email protected]>
Cc: kernel test robot <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mina Almasry <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Rolf Eike Beer <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Baolin Wang

arch/arm64/mm/hugetlbpage.c

@@ -368,6 +368,28 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
 	return NULL;
 }
 
+unsigned long hugetlb_mask_last_page(struct hstate *h)
+{
+	unsigned long hp_size = huge_page_size(h);
+
+	switch (hp_size) {
+#ifndef __PAGETABLE_PMD_FOLDED
+	case PUD_SIZE:
+		return PGDIR_SIZE - PUD_SIZE;
+#endif
+	case CONT_PMD_SIZE:
+		return PUD_SIZE - CONT_PMD_SIZE;
+	case PMD_SIZE:
+		return PUD_SIZE - PMD_SIZE;
+	case CONT_PTE_SIZE:
+		return PMD_SIZE - CONT_PTE_SIZE;
+	default:
+		break;
+	}
+
+	return 0UL;
+}
+
 pte_t arch_make_huge_pte(pte_t entry, unsigned int shift, vm_flags_t flags)
 {
 	size_t pagesize = 1UL << shift;