static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
		unsigned long haddr, pmd_t *pmd)
{
	struct mm_struct *mm = vma->vm_mm;
	pgtable_t pgtable;
	pmd_t _pmd, old_pmd;
	int i;

	/*
	 * Leave pmd empty until pte is filled note that it is fine to delay
	 * notification until mmu_notifier_invalidate_range_end() as we are
	 * replacing a zero pmd write protected page with a zero pte write
	 * protected page.
	 *
	 * See Documentation/vm/mmu_notifier.rst
	 */
	old_pmd = pmdp_huge_clear_flush(vma, haddr, pmd);

	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
	pmd_populate(mm, &_pmd, pgtable);

	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
		pte_t *pte, entry;
		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
		entry = pte_mkspecial(entry);
		if (pmd_uffd_wp(old_pmd))
			entry = pte_mkuffd_wp(entry);
		pte = pte_offset_map(&_pmd, haddr);
		VM_BUG_ON(!pte_none(*pte));
		set_pte_at(mm, haddr, pte, entry);
		pte_unmap(pte);
	}
	smp_wmb(); /* make pte visible before pmd */
	pmd_populate(mm, pmd, pgtable);
}
