mm/hugetlb: check for unreasonable folio sizes when registering hstate

Let's check that no hstate that corresponds to an unreasonable folio size
is registered by an architecture.  If we were to succeed registering, we
could later try allocating an unsupported gigantic folio size.

Further, let's add a BUILD_BUG_ON() for checking that HUGETLB_PAGE_ORDER
is sane at build time.  As HUGETLB_PAGE_ORDER is dynamic on powerpc, we
have to use a BUILD_BUG_ON_INVALID() to make it compile.

No existing kernel configuration should be able to trigger this check:
either SPARSEMEM without SPARSEMEM_VMEMMAP cannot be configured or
gigantic folios will not exceed a memory section (the case on sparse).

Link: https://lkml.kernel.org/r/20250901150359.867252-9-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: davidhildenbrand

mm/hugetlb.c

@@ -4657,6 +4657,7 @@ static int __init hugetlb_init(void)
 
 	BUILD_BUG_ON(sizeof_field(struct page, private) * BITS_PER_BYTE <
 			__NR_HPAGEFLAGS);
+	BUILD_BUG_ON_INVALID(HUGETLB_PAGE_ORDER > MAX_FOLIO_ORDER);
 
 	if (!hugepages_supported()) {
 		if (hugetlb_max_hstate || default_hstate_max_huge_pages)
@@ -4740,6 +4741,7 @@ void __init hugetlb_add_hstate(unsigned int order)
 	}
 	BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE);
 	BUG_ON(order < order_base_2(__NR_USED_SUBPAGE));
+	WARN_ON(order > MAX_FOLIO_ORDER);
 	h = &hstates[hugetlb_max_hstate++];
 	__mutex_init(&h->resize_lock, "resize mutex", &h->resize_key);
 	h->order = order;