// SPDX-License-Identifier: GPL-2.0-only
/*
 * Linux v6.18, arch/x86/mm/init.c:127-168
 * Source: https://github.com/torvalds/linux/blob/v6.18/arch/x86/mm/init.c
 * Complete function: alloc_low_pages
 * Body unchanged. Kernel dependencies are not bundled.
 * License text: GPL-2.0.txt
 * Source has no SPDX header; license follows kernel COPYING.
 */

__ref void *alloc_low_pages(unsigned int num)
{
	unsigned long pfn;
	int i;

	if (after_bootmem) {
		unsigned int order;

		order = get_order((unsigned long)num << PAGE_SHIFT);
		return (void *)__get_free_pages(GFP_ATOMIC | __GFP_ZERO, order);
	}

	if ((pgt_buf_end + num) > pgt_buf_top || !can_use_brk_pgt) {
		unsigned long ret = 0;

		if (min_pfn_mapped < max_pfn_mapped) {
			ret = memblock_phys_alloc_range(
					PAGE_SIZE * num, PAGE_SIZE,
					min_pfn_mapped << PAGE_SHIFT,
					max_pfn_mapped << PAGE_SHIFT);
		}
		if (!ret && can_use_brk_pgt)
			ret = __pa(extend_brk(PAGE_SIZE * num, PAGE_SIZE));

		if (!ret)
			panic("alloc_low_pages: can not alloc memory");

		pfn = ret >> PAGE_SHIFT;
	} else {
		pfn = pgt_buf_end;
		pgt_buf_end += num;
	}

	for (i = 0; i < num; i++) {
		void *adr;

		adr = __va((pfn + i) << PAGE_SHIFT);
		clear_page(adr);
	}

	return __va(pfn << PAGE_SHIFT);
}