From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.12 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793695316; b=UlTsCxy1zlExi1FqH1Pw+8DdQ2wf+Zwgn/vR5eGJk5RZ/1DRxoEMlib7zz0CFo+9a0dk 2fMAy+5Onh9+HmtW+JRhzW7Ja3EGoORhTRaXXZRmEuanqaSYc5Hx8CU4pDpPdhy6Pbzqb S5QSEStE6Q3lGX//wOoeQnLkHE7F2xgAWxY9QF69DYhYp0Omu2t/G0tjHtYUM11CCvuPY PuJ2vHT85nDIxMAs++9oeVdT+qrbHO9d+lhuubgFb7a1oE9qd0A6lzJxily7ERXzOeBWE oEQu8vly/F/Cl2Mubf2mh+xxy5rqNZ0cze27u8yyhSwTFpiwQiNt5sbItGkYcBouUKg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793695316; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Content-Type:Mime-Version:Subject:From: In-Reply-To:Date:Cc:Content-Transfer-Encoding:Message-Id:References: To:X-Mailer; bh=r35ebxTXAFp75IFXPLib2rMbuUcQ84dYXkx8V7iwL8A=; b=ih3XrKW3VdXNpGfpSbhoIFfB4UAASzL2c/9h7Y6E1Kpyw+0tj0QclEmfALnCgAv0hExw Z4uo6JBxDXeA5UYIYdd+9OktwjxGxRZG9KywSMNe87p2Y6wU2gmaT+L+bVMgIeMo0Q8iX gv4BvkDdmpQlZ+LqM6OAR+AcY2tndMZlVKNY6ze4EKFM3OhCTPgwGjHlAB3Ydn5I/CmX/ avncjq6gTdOgLQNFhoXnlO3McW9r/iBAtTQx5hXjBKZOSgqKtjLltlKYex4LMdmNJfi9q 4TYux6LlYlvr1HNbj5RDWSKzMaxFCyvEWzDMHVs5O2fqHH/Ox/Xux/49VaqECUsO0Aw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=XK1DYUpv; arc=none smtp.remote-ip=95.215.58.12 Received: from mta1.migadu.com (out-12.mta1.migadu.com [95.215.58.12]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 64CE6606C69E for ; Tue, 3 Nov 2026 08:41:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 64CE6606C69E Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=XK1DYUpv X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=r35ebxTXAFp75IFXPLib2rMbuUcQ84dYXkx8V7iwL8A=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793695313; v=1; x=1794300113; b=XK1DYUpvLk5CYvkb7JFC+S4lsX1Qqv4eUJlrtaue3W3zZb7pCf3qpo4zLyxKVIkvEtUzWZ+4 S7M1RAa8eGkZH3JNO6bg+/5kwjAD1+ljLXL5I4B0+hAixXEB+fxlf7+rJokMyImgQB9peBBDw9m TU5YoENfR5BdtdIOzbGdNBa8= X-Envelope-To: linux-kernel@vger.kernel.org Received: by mta12.migadu.com with ESMTPS id 06b8647df261ab87; Tue, 03 Nov 2026 08:41:53 +0000 X-Mizu-Trace-ID: 06b8647df261ab87 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii 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 (Mac OS X Mail 16.0 \(3901.200.71.1.16\)) Subject: Re: [PATCH 1/4] x86: hugetlb: disable default CMA reservations on 32-bit kernel From: Muchun Song In-Reply-To: <61eee83da19a87337e68a7747fc0b89ee5d0393b.1793692578.git.zhengqi.arch@bytedance.com> Date: Tue, 3 Nov 2026 16:41:38 +0800 Cc: osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org, azpijr@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Qi Zheng , stable@vger.kernel.org, x86@kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <4EE65C7C-3532-4056-9794-47A9B894969F@linux.dev> References: <61eee83da19a87337e68a7747fc0b89ee5d0393b.1793692578.git.zhengqi.arch@bytedance.com> To: Qi Zheng X-Mailer: Apple Mail (2.3901.200.71.1.16) > On Nov 3, 2026, at 16:01, Qi Zheng wrote: >=20 > From: Qi Zheng >=20 > A 32-bit x86 kernel can run on a 64-bit-capable CPU advertising = GBPAGES. I don't think anyone would do that. That said, it is genuinely an issue. > 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=3D can therefore reserve a CMA area that cannot > serve the intended gigantic HugeTLB allocations. >=20 > 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 <=3D MAX_PAGE_ORDER) check in hugetlb_cma_reserve(), > warning that hugetlb_cma is attempting to reserve a non-gigantic = order. >=20 > Require CONFIG_X86_64 as well as GBPAGES when selecting the default = CMA > order to avoid these ineffective reservations. >=20 > Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic = hugepages using cma") > Cc: stable@vger.kernel.org > Cc: x86@kernel.org > Signed-off-by: Qi Zheng Acked-by: Muchun Song Thanks.