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 4787BC88E77 for ; Wed, 16 Sep 2026 13:35:01 +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:References:Cc:To:From: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=0pwhDPf1ZcMsFXr2wFtOfi9zYP8FgQyGaMxEJBJLxLs=; b=ZbRu/OnmHobg7JGtSFpOD1StbB 4ZIK8N6Nek/KrYK2SOxYHm++p8cWOzX/MBDVXD7xSgizhEOF5XGP5aLBSazVBcz8UD+VRL2UrGqQD dyQ+E99U8zwNKv/czHxYOl1qYUXdOWGpuhNvNuodZKkAy3LdzYVvKXjVr1AkbNJ7gfalSZ8FhKm7x qlfHCyuiUDmX/zwD4DwmrrpMPtjSTf3bcf5NH4vQM53i5icmoJ9ne/dzDPn1mzcWfFGgIrqzPHkdq Svau94BrmgMFojb7s1Jrs/IVB9gFe8jmvUImLQNf6kIJ8nQcxdVEiDksXMd0NUVRraKG2RrhdroMg PKXulT8Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6pmm-00000009H0u-0rVF; Wed, 16 Sep 2026 13:34:52 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6pmQ-00000009Gx7-1vyh for linux-arm-kernel@lists.infradead.org; Wed, 16 Sep 2026 13:34:30 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 7F7DD6057A; Wed, 16 Sep 2026 13:34:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B0531F00899; Wed, 16 Sep 2026 13:34:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789565669; bh=0pwhDPf1ZcMsFXr2wFtOfi9zYP8FgQyGaMxEJBJLxLs=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=AK/o8eNsta406tALZ4n9LY9LZcOKGvZzHbQFlv4LP5s4xN7btezfxtDaU9z81nya+ l6U8c5hPVqwXmGK/Kl0DYNG4ENW9dbQNIkJwlLwoiRsvbF2S7+CCFUKopJXF78x2wp qtg8qNMIMIr8JhD+3m3EU4wdBXE1Vdh8nuk5QpIwFq+AJ/w0/372Fan5CtjG06xRDO cZFRNtt/b06Dt6qADOU/M9gHizfEDHokFdaBR03wKLBw/+ZcKTW/5ZG0aWDVpccajh NHNe4gIQm7cJHXhzEGDMJjNRiYJyXS/umqRLIBpjKwnB2O4sntJSe1exsXm+zqiRTL T9FweJd2d5C/w== Message-ID: <0deef591-d82a-4034-9514-abde0e73e5e5@kernel.org> Date: Wed, 16 Sep 2026 15:34:24 +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 From: "David Hildenbrand (Arm)" 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> 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 9/16/26 15:32, David Hildenbrand (Arm) wrote: > 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) > Whops, accidentally stumbled into v1 in my inbox after starting to look at v2 :D -- Cheers, David