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[80.187.83.189]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8ab8b0sm33676902f8f.18.2025.10.09.02.20.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Oct 2025 02:20:29 -0700 (PDT) Message-ID: <1db15a30-72d6-4045-8aa1-68bd8411b0ba@redhat.com> Date: Thu, 9 Oct 2025 11:20:24 +0200 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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> <9361c75a-ab37-4d7f-8680-9833430d93d4@redhat.com> <03671aa8-4276-4707-9c75-83c96968cbb2@csgroup.eu> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 09.10.25 11:16, Christophe Leroy wrote: > > > Le 09/10/2025 à 10:14, David Hildenbrand a écrit : >> 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. > > I'm trying to dig into history and when looking at commit 4eb0716e868e > ("hugetlb: allow to free gigantic pages regardless of the > configuration") I understand that CONFIG_ARCH_HAS_GIGANTIC_PAGE is > needed to be able to allocate gigantic pages at runtime. It is not > needed to reserve gigantic pages at boottime. > > What am I missing ? That CONFIG_ARCH_HAS_GIGANTIC_PAGE has nothing runtime-specific in its name. Can't we just select CONFIG_ARCH_HAS_GIGANTIC_PAGE for the relevant hugetlb config that allows for *gigantic pages*. -- Cheers David / dhildenb