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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F2883C433EF for ; Fri, 15 Apr 2022 09:51:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351876AbiDOJyR (ORCPT ); Fri, 15 Apr 2022 05:54:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230247AbiDOJyO (ORCPT ); Fri, 15 Apr 2022 05:54:14 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1DE24B6E6B for ; Fri, 15 Apr 2022 02:51:47 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B52876219F for ; Fri, 15 Apr 2022 09:51:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0D5D7C385A6; Fri, 15 Apr 2022 09:51:43 +0000 (UTC) Date: Fri, 15 Apr 2022 10:51:40 +0100 From: Catalin Marinas To: Herbert Xu Cc: Ard Biesheuvel , Will Deacon , Marc Zyngier , Arnd Bergmann , Greg Kroah-Hartman , Andrew Morton , Linus Torvalds , Linux Memory Management List , Linux ARM , Linux Kernel Mailing List , "David S. Miller" Subject: Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 15, 2022 at 03:51:54PM +0800, Herbert Xu wrote: > On Fri, Apr 15, 2022 at 09:49:12AM +0200, Ard Biesheuvel wrote: > > I'm not sure I understand what would go wrong if that assumption no > > longer holds. > > It's very simple, we don't do anything to the pointer returned > by kmalloc before returning it as a tfm or other object with > an alignment of CRYPTO_MINALIGN. IOW if kmalloc starts returning > pointers that are not aligned to CRYPTO_MINALIGN then we'd be > lying to the compiler. I agree that it would be lying to the compiler, but I don't think this matters for arm64 where the CPU can do unaligned accesses just fine. We don't even end up with unaligned accesses here. Let's say we have: struct x { ... } __attribute__ ((__aligned__ (128))); and the kmalloc(sizeof(struct x)) returns a 64-byte aligned pointer. The compiler-generated code won't have any problem on arm64 accessing the struct x members. As I said a few times, it's not affecting any other architecture and not breaking arm64 either. Anyway, let's agree to disagree. I'll look into keeping CRYPTO_MINALIGN as ARCH_KMALLOC_MINALIGN and introduce a CRYPTO_DMA_MINALIGN (or just use ARCH_DMA_MINALIGN directly) together with something like Linus' dma_kmalloc() in places where an object aligned to ARCH_DMA_MINALIGN is needed in the crypto code. -- Catalin