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 29E47C433F5 for ; Sun, 17 Apr 2022 08:38:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233672AbiDQIlZ (ORCPT ); Sun, 17 Apr 2022 04:41:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229460AbiDQIlX (ORCPT ); Sun, 17 Apr 2022 04:41:23 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9162E63F5 for ; Sun, 17 Apr 2022 01:38:48 -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 ams.source.kernel.org (Postfix) with ESMTPS id 425A3B80AAD for ; Sun, 17 Apr 2022 08:38:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8B32C385A4; Sun, 17 Apr 2022 08:38:43 +0000 (UTC) Date: Sun, 17 Apr 2022 09:38:40 +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 Sun, Apr 17, 2022 at 04:11:22PM +0800, Herbert Xu wrote: > On Fri, Apr 15, 2022 at 01:31:32PM +0100, Catalin Marinas wrote: > > > > This needs a clarification. For the above structure, kmalloc() will > > return a 128-byte aligned pointer since sizeof(x) is a multiple of 128. > > The potential problem is if you have something like: > > > > kmalloc(sizeof(struct x) + 64); > > > > The above could end up as a kmalloc(192) which is available with an > > ARCH_KMALLOC_MINALIGN of 64. If that's a real use-case, I can change the > > slab patch to not create the 192 (or 48 if we go for an even smaller > > ARCH_KMALLOC_MINALIGN) caches and we'd always have ARCH_DMA_MINALIGN > > guarantee if the structure itself is correctly aligned. No lying to the > > compiler. > > Yes I suppose that should work: > > 1) Enlarge each crypto API object so that they're >= 128 bytes; I don't think we need to do anything here. A structure like: struct x { char y; char z[] CRYPTO_MINALIGN_ATTR; }; is already of size 128. Without CRYPTO_MINALIGN_ATTR, its size would be 1 but otherwise the whole structure inherits the alignment of its member and this translates into an aligned size. > 2) Modify kmalloc so that for sizes >= 128 bytes they're padded > to multiples of 128. This doesn't look like a hack, we want to honour the power of 2 alignments. -- Catalin