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Tue, 03 Nov 2026 08:20:26 +0000 X-Mizu-Trace-ID: d5aaef5f702bfade X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=utf-8 X-Archived-By: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.200.71.1.16\)) Subject: Re: [PATCH] mm/hugetlb: fix validation of unsupported HugeTLB orders From: Muchun Song In-Reply-To: Date: Tue, 3 Nov 2026 16:20:08 +0800 Cc: Muchun Song , Andrew Morton , Oscar Salvador , David Hildenbrand , Kiryl Shutsemau , Mike Rapoport , Huacai Chen , WANG Xuerui , linux-mm@kvack.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20261103023831.1805473-1-songmuchun@bytedance.com> To: sashiko-reviews@lists.linux.dev X-Mailer: Apple Mail (2.3901.200.71.1.16) X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 33D891C0005 X-Stat-Signature: n9drnb8csckwmwb1igkc54gdpe6mjhor X-Rspam-User: X-HE-Tag: 1793694030-158088 X-HE-Meta: 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 CMukiAZ2 zxAitekjUdMKAdp1WowCrly4oHVySt53/yh5o6HVxjI8Np4+Nvc6xoYf2fxyXFonaWd3wCrWDGfD0i/cSRfAnOqo0bBtW1xrQGTsJE0wpLKP9RZApwSR48NVadr3HUfdc+g7taBybIJP3XxIQD5EBSo0EgwWNFmabf29/mIYcEeeZQ7y/pMbSUS166+U0RzeLZDzmadX5s3bkgIWSD9PG8YKmBeHDPNMWbmrc7G6D/LcnGanrY4Cby/W6VZEuWvo7ixtHWEWADNUUMQCZWxnW9IvmRFeivBgMa23OBCClG3QejKd7At+Hd7h6N32deAr09SrjLy/H/nzlnm9uBDmFTx7RePP9WdoaHBIKt1/130SpNYshiNjG2daoVg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 > On Nov 3, 2026, at 16:13, sashiko-bot@kernel.org wrote: >=20 > Thank you for your contribution! Sashiko AI review found 1 potential = issue(s) to consider: > - [High] mm/hugetlb: boot BUG_ON() in hugetlb_init() when HPAGE_SHIFT = is 0 on powerpc > -- >=20 > commit 83959b12982c256d20ca0de51021b3beae201569 > Author: Muchun Song >=20 > mm/hugetlb: fix validation of unsupported HugeTLB orders >=20 > This commit replaces BUILD_BUG_ON_INVALID() with MAYBE_BUILD_BUG_ON() = in > hugetlb_init() so that configurations where HUGETLB_PAGE_ORDER exceeds > MAX_FOLIO_ORDER are rejected at build time when constant or via = BUG_ON() at > runtime otherwise. >=20 >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index ff9dbfbc7a961..e21ac667694bd 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -4181,7 +4181,7 @@ static int __init hugetlb_init(void) >>=20 >> BUILD_BUG_ON(sizeof_field(struct page, private) * BITS_PER_BYTE = < >> __NR_HPAGEFLAGS); >> - BUILD_BUG_ON_INVALID(HUGETLB_PAGE_ORDER > MAX_FOLIO_ORDER); >> + MAYBE_BUILD_BUG_ON(HUGETLB_PAGE_ORDER > MAX_FOLIO_ORDER); >=20 > [Severity: High] > Will placing MAYBE_BUILD_BUG_ON() before the hugepages_supported() = check in > hugetlb_init() trigger a boot BUG_ON() on architectures like PowerPC > Book3S-64 when huge pages are unsupported at runtime? Yeah, it's easy to fix, but I'll wait another day before updating = it=E2=80=94just in case others have feedback. Thanks, Muchun >=20 > On CONFIG_PPC_BOOK3S_64, arch/powerpc/include/asm/page.h defines = HPAGE_SHIFT > as a runtime unsigned int variable: >=20 > extern unsigned int hpage_shift; > #define HPAGE_SHIFT hpage_shift > ... > #define HUGETLB_PAGE_ORDER (HPAGE_SHIFT - PAGE_SHIFT) >=20 > Because hpage_shift is not a compile-time constant, = MAYBE_BUILD_BUG_ON() > expands to a runtime BUG_ON(HUGETLB_PAGE_ORDER > MAX_FOLIO_ORDER). >=20 > When huge pages are not supported by the platform or are disabled at = boot > (for example, when hugetlbpage_init_defaultsize() in > arch/powerpc/mm/book3s64/hugetlbpage.c finds no supported huge page = sizes), > hpage_shift remains 0, which hugepages_supported() checks: >=20 > static inline bool hugepages_supported(void) > { > if (hugetlb_disabled) > return false; >=20 > return HPAGE_SHIFT !=3D 0; > } >=20 > Evaluating HUGETLB_PAGE_ORDER before checking hugepages_supported() = computes > (0U - PAGE_SHIFT) in unsigned int arithmetic, wrapping around to a = large > unsigned value that exceeds MAX_FOLIO_ORDER and hits BUG_ON(). >=20 > Should MAYBE_BUILD_BUG_ON(HUGETLB_PAGE_ORDER > MAX_FOLIO_ORDER) be = moved > after the if (!hugepages_supported()) block in hugetlb_init(), similar = to how > hugepage_init() in mm/huge_memory.c checks has_transparent_hugepage() = before > evaluating MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER > MAX_PAGE_ORDER)? >=20 > --=20 > Sashiko AI review =C2=B7 = https://sashiko.dev/#/patchset/20261103023831.1805473-1-songmuchun@bytedan= ce.com?part=3D1