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

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Message-ID: <fa3425dd-df25-4a0b-a27e-614c81d301c4@lucifer.local>
Date: Thu, 28 Aug 2025 15:45:39 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brendan Jackman <jackmanb@...gle.com>,
        Christoph Lameter <cl@...two.org>, Dennis Zhou <dennis@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>, dri-devel@...ts.freedesktop.org,
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        John Hubbard <jhubbard@...dia.com>, kasan-dev@...glegroups.com,
        kvm@...r.kernel.org, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
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Subject: 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 <david@...hat.com>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  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
>