From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 75C46C88E5C for ; Wed, 16 Sep 2026 13:32:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=DKoMOvgofwktZmoUuUYwgSaKNRpTiD37gRdhxHcH9IM=; b=JjnsK6iHCYBuARBUs0DugXPXq7 YSO+qs2+LvdFQNzyXhjcgS5NRx5crSMKWX6tgGirOtwa98nn/agOqWVm2Th26QwHAJw2KinRXj7lN uVWEBde49l745dwQ4/yYqgjZoG3x/5qtmxfdFGGC6CoLJUKzjm5Q9MOaNgkf43QXnuvm02mDu3yLm RDmoVS12zGfM7ekicRHcXNIfJygzjYxHpOM+ViYrJUORZ7HnW+kYcYY7g9PpByqFit5Ykdvnnle4a 9EmrV3W/mqgACG1rcZN0QPF16/JRXqs+3+Y6rYAJv1jtiRMVilBGcsmklyFE2aAnJdNicfwjlfnfG D7DTtruw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6pkM-00000009GiV-0KxY; Wed, 16 Sep 2026 13:32:22 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6pkL-00000009GiO-0FP7 for linux-arm-kernel@lists.infradead.org; Wed, 16 Sep 2026 13:32:21 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 3EAC5602CB; Wed, 16 Sep 2026 13:32:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E936F1F000FF; Wed, 16 Sep 2026 13:32:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789565540; bh=DKoMOvgofwktZmoUuUYwgSaKNRpTiD37gRdhxHcH9IM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bNk89v3Rdvd38fFvrhXtrco6p421SlhJ1qFm7IaLPOFUxKu/h9ghCRcc6TBl0FUuk pW+G8O/SLu4S/+mCwe2OGNjQSRU2vzMj9hu4UtooAkrxqP2dSN2cn5H48m33qMrL+D Yshy7d9e/IVpTidQ8mlVvmca86Od3soaTPQ54nJxtI6XF7I0RSAkuCsVS7Hgp+gbNx NQ8xPZFF3vSt+TF0bJnYpRuN2Gr2FKJ1uTPzwS5UG2CJjq5m4OiIGddUfm0dn0oN/V HZ1XMKE3+y6o6z/iD2WbXm8GPrr95SNcSbdHw/DF0gDeYQJTa0ysNz7EVh2t23BdXM wDAvvkmOWtTTQ== Message-ID: Date: Wed, 16 Sep 2026 15:32:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/17] arm64/mm: Convert READ_ONCE() as pmdp_get() while accessing PMD To: Anshuman Khandual , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, Mark Rtland , linx-arm-kernel@lists.infradead.org, linx-kernel@vger.kernel.org, kasan-dev@googlegrops.com References: <20260729122452.3797443-1-anshuman.khandual@arm.com> <20260729122452.3797443-3-anshuman.khandual@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 7/29/26 14:24, Anshuman Khandual wrote: > Convert all READ_ONCE() based PMD accesses as pmdp_get() instead which will > support both D64 and D128 translation regime going forward. That is because > READ_ONCE() would need 128 bit single copy atomic guarantees, while reading > 128 bit page table entries which is currently not supported on arm64. Build > fails for READ_ONCE() while accessing beyond 64 bits. > > Load Pair/Store Pair (ldp/stp) are only single copy atomic if FEAT_LSE128 > is supported (which is required when FEAT_D128 is supported). Currently 128 > bit pgtables is a compile time decision - so we could have chosen to extend > READ_ONCE()/WRITE_ONCE() to allow 128 bit for this configuration. But then > it's a general purpose API and we were concerned that other users might > eventually creep in that expect 128 and then fail to compile in the other > configs. > > But worse, we are considering eventually making D128 a boot time option, at > which point we'd have to make READ_ONCE() always allow 128 bit at compile > time but then it might silently tear at runtime. > > So our preference is to standardize on these existing helpers, which we can > override in arm64 to give the 128 bit single copy guarantee when required. > Best to mention here that no functional change is expect because the common-cde pmdp_get() etc helpers do exactly that. Reviewed-by: David Hildenbrand (Arm) -- Cheers, David