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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <faf62f20-8844-42a0-a7a7-846d8ead0622@csgroup.eu>
Date: Thu, 9 Oct 2025 10:04:34 +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 :
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 1e777cc51ad04..d3542e92a712e 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;
> 
> We end up registering hugetlb folios that are bigger than 
> MAX_FOLIO_ORDER. So we have to figure out how a config can trigger that 
> (and if we have to support that).
> 

MAX_FOLIO_ORDER is defined as:

#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
#define MAX_FOLIO_ORDER		PUD_ORDER
#else
#define MAX_FOLIO_ORDER		MAX_PAGE_ORDER
#endif

MAX_PAGE_ORDER is the limit for dynamic creation of hugepages via 
/sys/kernel/mm/hugepages/ but bigger pages can be created at boottime 
with kernel boot parameters without CONFIG_ARCH_HAS_GIGANTIC_PAGE:

   hugepagesz=64m hugepages=1 hugepagesz=256m hugepages=1

Gives:

HugeTLB: registered 1.00 GiB page size, pre-allocated 0 pages
HugeTLB: 0 KiB vmemmap can be freed for a 1.00 GiB page
HugeTLB: registered 64.0 MiB page size, pre-allocated 1 pages
HugeTLB: 0 KiB vmemmap can be freed for a 64.0 MiB page
HugeTLB: registered 256 MiB page size, pre-allocated 1 pages
HugeTLB: 0 KiB vmemmap can be freed for a 256 MiB page
HugeTLB: registered 4.00 MiB page size, pre-allocated 0 pages
HugeTLB: 0 KiB vmemmap can be freed for a 4.00 MiB page
HugeTLB: registered 16.0 MiB page size, pre-allocated 0 pages
HugeTLB: 0 KiB vmemmap can be freed for a 16.0 MiB page

Christophe