linux-kernel - Re: (bisected) [PATCH v2 08/37] mm/hugetlb: check for unreasonable folio sizes when registering hstate

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Message-ID: <1fb2259f-65e1-4cd0-ae70-b355843970e4@csgroup.eu>
Date: Thu, 9 Oct 2025 09:44:30 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc: Zi Yan <ziy@...dia.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 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, intel-gfx@...ts.freedesktop.org,
 iommu@...ts.linux.dev, io-uring@...r.kernel.org,
 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,
 Linus Torvalds <torvalds@...ux-foundation.org>, linux-arm-kernel@...s.com,
 linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
 linux-ide@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-mips@...r.kernel.org, linux-mmc@...r.kernel.org, linux-mm@...ck.org,
 linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
 linux-scsi@...r.kernel.org, Marco Elver <elver@...gle.com>,
 Marek Szyprowski <m.szyprowski@...sung.com>, Michal Hocko <mhocko@...e.com>,
 Mike Rapoport <rppt@...nel.org>, Muchun Song <muchun.song@...ux.dev>,
 netdev@...r.kernel.org, Oscar Salvador <osalvador@...e.de>,
 Peter Xu <peterx@...hat.com>, Robin Murphy <robin.murphy@....com>,
 Suren Baghdasaryan <surenb@...gle.com>, Tejun Heo <tj@...nel.org>,
 virtualization@...ts.linux.dev, Vlastimil Babka <vbabka@...e.cz>,
 wireguard@...ts.zx2c4.com, x86@...nel.org,
 "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: (bisected) [PATCH v2 08/37] mm/hugetlb: check for unreasonable
 folio sizes when registering hstate

Le 09/10/2025 à 09:22, David Hildenbrand a écrit :
> On 09.10.25 09:14, Christophe Leroy wrote:
>> Hi David,
>>
>> Le 01/09/2025 à 17:03, David Hildenbrand a écrit :
>>> 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).
>>>
>>> Reviewed-by: Zi Yan <ziy@...dia.com>
>>> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>>> Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>
>>> Signed-off-by: David Hildenbrand <david@...hat.com>
>>
>> I get following warning on powerpc with linus tree, bisected to commit
>> 7b4f21f5e038 ("mm/hugetlb: check for unreasonable folio sizes when
>> registering hstate")
> 
> Do you have the kernel config around? Is it 32bit?
> 
> That would be helpful.

That's corenet64_smp_defconfig

Boot on QEMU with:

	qemu-system-ppc64 -smp 2 -nographic -M ppce500 -cpu e5500 -m 1G

Christophe