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[80.187.83.189]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46fa9d6fb41sm71628175e9.17.2025.10.09.01.14.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Oct 2025 01:14:07 -0700 (PDT) Message-ID: <9361c75a-ab37-4d7f-8680-9833430d93d4@redhat.com> Date: Thu, 9 Oct 2025 10:14:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: (bisected) [PATCH v2 08/37] mm/hugetlb: check for unreasonable folio sizes when registering hstate To: Christophe Leroy , linux-kernel@vger.kernel.org Cc: Zi Yan , Lorenzo Stoakes , "Liam R. Howlett" , Alexander Potapenko , Andrew Morton , Brendan Jackman , Christoph Lameter , Dennis Zhou , Dmitry Vyukov , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux.dev, io-uring@vger.kernel.org, Jason Gunthorpe , Jens Axboe , Johannes Weiner , John Hubbard , kasan-dev@googlegroups.com, kvm@vger.kernel.org, Linus Torvalds , linux-arm-kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-ide@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Marco Elver , Marek Szyprowski , Michal Hocko , Mike Rapoport , Muchun Song , netdev@vger.kernel.org, Oscar Salvador , Peter Xu , Robin Murphy , Suren Baghdasaryan , Tejun Heo , virtualization@lists.linux.dev, Vlastimil Babka , wireguard@lists.zx2c4.com, x86@kernel.org, "linuxppc-dev@lists.ozlabs.org" References: <20250901150359.867252-1-david@redhat.com> <20250901150359.867252-9-david@redhat.com> <3e043453-3f27-48ad-b987-cc39f523060a@csgroup.eu> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251009_011411_608425_14BFFA8C X-CRM114-Status: GOOD ( 15.55 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 09.10.25 10:04, Christophe Leroy wrote: > > > 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 I think it's a violation of CONFIG_ARCH_HAS_GIGANTIC_PAGE. The existing folio_dump() code would not handle it correctly as well. See how snapshot_page() uses MAX_FOLIO_NR_PAGES. -- Cheers David / dhildenb