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Tue, 03 Nov 2026 03:40:22 -0800 (PST) Received: from [192.168.1.22] ([83.231.69.9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e71bab1a8sm24248670f8f.57.2026.11.03.03.40.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); 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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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 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