Re: [PATCH v1 08/36] mm/hugetlb: check for unreasonable folio sizes when registering hstate

On Thu, Aug 28, 2025 at 12:01:12AM +0200, David Hildenbrand wrote:
> 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).

I am guessing it's implicit that MAX_FOLIO_ORDER <= section size?

>
> Signed-off-by: David Hildenbrand <[email protected]>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <[email protected]>

> ---
>  mm/hugetlb.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 572b6f7772841..4a97e4f14c0dc 100644
> --- a/mm/hugetlb.c
> +++ b/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;
> --
> 2.50.1
>