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

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Message-ID: <5f6e49fa-4c1c-4ece-ba67-0e140e2685da@redhat.com>
Date: Fri, 29 Aug 2025 12:07:44 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.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>,
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 dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
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 Jason Gunthorpe <jgg@...dia.com>, Jens Axboe <axboe@...nel.dk>,
 Johannes Weiner <hannes@...xchg.org>, 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>, linux-arm-kernel@...s.com,
 linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
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Subject: Re: [PATCH v1 08/36] mm/hugetlb: check for unreasonable folio sizes
 when registering hstate

On 28.08.25 16:45, Lorenzo Stoakes wrote:
> 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?

Yes, we have a build-time bug that somewhere.

-- 
Cheers

David / dhildenb