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b=TpbPfdgWbH6gGD1XVstA3oJT7b5CDkZRmfmPvVlwNVz4gi1txWb4MKNvOd82hHgzx M5n8Hmb/YE7vOWlwMKHpqWHPpRRa9p7m0CXdDzdArFmMwW8329BlYcDhHpVfpkbf9t XsDszlEngFjzmH/tsneOFgvuRQ0B4NUL7WOT0fTxGOXmR0Y8sateaDFB1Uvp7/riDW cpyHu51t9NjfjbOmkgb/P/0Cj+GSqjjP+yqXVo0GINez7r4zd34ot8676o2QweXQhB O/isZNK0GboRZ8H9gaLSOhM8H/HMh1YB+Eyum/mnnJ6C5UeIf/aN47XVz+8g59wzdS YcSuMUyFfZUIQ== Date: Thu, 5 Nov 2026 10:29:22 +0100 From: "Oscar Salvador (SUSE)" To: Qi Zheng Cc: muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org, azpijr@gmail.com, lance.yang@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Qi Zheng , stable@vger.kernel.org Subject: Re: [PATCH v2 1/4] x86: hugetlb: disable default CMA reservations on 32-bit kernel Message-ID: References: X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: szfdhia3sza851qezgugdii65x1s3xeq X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 1EB0920002 X-HE-Tag: 1793870967-602062 X-HE-Meta: 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 bqiYERex /YiniMMONipN8pN/owvRVPYHa7tZRAOWbmeViJAfkjy9+titqrpZWUp/WvJXM5D9ib48tbGTXgToEDMUPkieZ9bfIBx3Vyp6knZ+dX6+ELWAmoaXVGaeklEFF6IuYDUkQP3Dn6H3jpXEpy4HKnMwhv+W6mKfw7fwzP1hscHLXAF6D17HhyZzrkbgczSq0HXLImUG7a8oYkvAUTqj5RRiMpDyj3bE9dYCzI9V/iyxaVhILbY7apPcMAssFEHwghG0jLbSENjxW0sBm4FCXnZmPaWZbZ6wMq5irOE20 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 Thu, Nov 05, 2026 at 12:07:43PM +0800, Qi Zheng wrote: > From: Qi Zheng > > A 32-bit x86 kernel can run on a 64-bit-capable CPU advertising GBPAGES. > 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 > Signed-off-by: Qi Zheng > Acked-by: Muchun Song > Reviewed-by: Jose A. Perez de Azpillaga Acked-by: Oscar Salvador > --- > 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; > -- > 2.54.0 > -- Oscar Salvador SUSE Labs