// SPDX-License-Identifier: GPL-2.0
/*
 * Official Linux v6.18: arch/x86/mm/pgtable.c
 * Complete function; source lines 322-374.
 * Body unchanged. Kernel dependencies and configuration are required.
 * Source URL, SHA, commit, and license: provenance.json; GPL-2.0.txt.
 */

pgd_t *pgd_alloc(struct mm_struct *mm)
{
	pgd_t *pgd;
	pmd_t *u_pmds[MAX_PREALLOCATED_USER_PMDS];
	pmd_t *pmds[PREALLOCATED_PMDS];

	pgd = _pgd_alloc(mm);

	if (pgd == NULL)
		goto out;

	mm->pgd = pgd;

	if (sizeof(pmds) != 0 &&
			preallocate_pmds(mm, pmds, PREALLOCATED_PMDS) != 0)
		goto out_free_pgd;

	if (sizeof(u_pmds) != 0 &&
			preallocate_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS) != 0)
		goto out_free_pmds;

	if (paravirt_pgd_alloc(mm) != 0)
		goto out_free_user_pmds;

	/*
	 * Make sure that pre-populating the pmds is atomic with
	 * respect to anything walking the pgd_list, so that they
	 * never see a partially populated pgd.
	 */
	spin_lock(&pgd_lock);

	pgd_ctor(mm, pgd);
	if (sizeof(pmds) != 0)
		pgd_prepopulate_pmd(mm, pgd, pmds);

	if (sizeof(u_pmds) != 0)
		pgd_prepopulate_user_pmd(mm, pgd, u_pmds);

	spin_unlock(&pgd_lock);

	return pgd;

out_free_user_pmds:
	if (sizeof(u_pmds) != 0)
		free_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS);
out_free_pmds:
	if (sizeof(pmds) != 0)
		free_pmds(mm, pmds, PREALLOCATED_PMDS);
out_free_pgd:
	_pgd_free(mm, pgd);
out:
	return NULL;
}