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 8AC79C433F5 for ; Fri, 15 Apr 2022 12:19:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353196AbiDOMVc (ORCPT ); Fri, 15 Apr 2022 08:21:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49256 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241445AbiDOMVb (ORCPT ); Fri, 15 Apr 2022 08:21:31 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C5D9EBF969 for ; Fri, 15 Apr 2022 05:19:02 -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 sin.source.kernel.org (Postfix) with ESMTPS id 1C83BCE2C65 for ; Fri, 15 Apr 2022 12:19:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 15709C385A6; Fri, 15 Apr 2022 12:18:56 +0000 (UTC) Date: Fri, 15 Apr 2022 13:18:53 +0100 From: Catalin Marinas To: Ard Biesheuvel Cc: Herbert Xu , 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 10:05:21AM +0200, Ard Biesheuvel wrote: > On Fri, 15 Apr 2022 at 09:52, 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 guess that should be fixable. GIven that this is about padding > rather than alignment, we could do something like > > struct crypto_request { > union { > struct { > ... fields ... > }; > u8 __padding[ARCH_DMA_MINALIGN]; > }; > void __ctx[] __align(CRYPTO_MINALIGN); > }; > > And then hopefully, we can get rid of the padding once we fix drivers > doing non-cache coherent inbound DMA into those structures. But if we keep CRYPTO_MINALIGN as 128, don't we get the padding automatically? struct crypto_request { ... void *__ctx[] CRYPTO_MINALIGN_ATTR; }; __alignof__(struct crypto_request) == 128; sizeof(struct crypto_request) == N * 128 The same alignment and size is true for a structure like: struct crypto_alg { ... } CRYPTO_MINALIGN_ATTR; Any kmalloc() of sizeof(the above structures) will return a pointer aligned to 128, irrespective of what ARCH_KMALLOC_MINALIGN is. The problem is if you have a structure without any alignment attribute (just ABI default), making its sizeof() smaller than ARCH_DMA_MINALIGN. In this case kmalloc() could return a pointer aligned to something smaller. Is this the case in the crypto code today? I can see it uses the right alignment annotations already, no need for kmalloc() hacks. -- Catalin