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Tue, 03 Nov 2026 03:40:21 -0800 (PST) Message-ID: <897b0ea8-d2f4-42e9-ad22-e331c5b085c7@gmail.com> Date: Tue, 3 Nov 2026 12:40:20 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] x86: hugetlb: disable default CMA reservations on 32-bit kernel To: Qi Zheng , muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Qi Zheng , stable@vger.kernel.org, x86@kernel.org References: <61eee83da19a87337e68a7747fc0b89ee5d0393b.1793692578.git.zhengqi.arch@bytedance.com> Content-Language: en-US From: "Jose A. Perez de Azpillaga" In-Reply-To: <61eee83da19a87337e68a7747fc0b89ee5d0393b.1793692578.git.zhengqi.arch@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: uix3cazio7okukda1in6rj8mnfzarnog X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-13.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FORGED_GMAIL_RCVD,FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 99B44100005 X-HE-Tag: 1793706023-503056 X-HE-Meta: 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 cb8lXksC 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 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 11/3/26 9:01 AM, Qi Zheng wrote: > From: Qi Zheng > > A 32-bit x86 kernel can run on a 64-bit-capable CPU advertising GBPAGES. weird. anyway, LGTM: Reviewed-by: Jose A. Perez de Azpillaga > arch_hugetlb_cma_order() checks only this feature and returns a nonzero > order, although gigantic HugeTLB support on x86 requires CONFIG_X86_64. > Specifying hugetlb_cma= can therefore reserve a CMA area that cannot > serve the intended gigantic HugeTLB allocations. > > On non-PAE kernels, the folded PUD_SHIFT yields a 4 MiB order, which is > equal to MAX_PAGE_ORDER. With CONFIG_DEBUG_VM enabled, this triggers the > VM_WARN_ON(order <= MAX_PAGE_ORDER) check in hugetlb_cma_reserve(), > warning that hugetlb_cma is attempting to reserve a non-gigantic order. > > Require CONFIG_X86_64 as well as GBPAGES when selecting the default CMA > order to avoid these ineffective reservations. > > Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma") > Cc: stable@vger.kernel.org > Cc: x86@kernel.org > Signed-off-by: Qi Zheng > --- > arch/x86/mm/hugetlbpage.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c > index 3b26621c91286..70726a99ede7b 100644 > --- a/arch/x86/mm/hugetlbpage.c > +++ b/arch/x86/mm/hugetlbpage.c > @@ -45,7 +45,7 @@ arch_initcall(gigantic_pages_init); > > unsigned int __init arch_hugetlb_cma_order(void) > { > - if (boot_cpu_has(X86_FEATURE_GBPAGES)) > + if (IS_ENABLED(CONFIG_X86_64) && boot_cpu_has(X86_FEATURE_GBPAGES)) > return PUD_SHIFT - PAGE_SHIFT; > > return 0; -- cheers, jose a. p-a