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 605E8C433F5 for ; Tue, 12 Apr 2022 12:57:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354813AbiDLM7d (ORCPT ); Tue, 12 Apr 2022 08:59:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56668 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355121AbiDLM5t (ORCPT ); Tue, 12 Apr 2022 08:57:49 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7368459A74 for ; Tue, 12 Apr 2022 05:31:28 -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 01532B81CD8 for ; Tue, 12 Apr 2022 12:31:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8FDBAC385A5; Tue, 12 Apr 2022 12:31:23 +0000 (UTC) Date: Tue, 12 Apr 2022 13:31:20 +0100 From: Catalin Marinas To: Herbert Xu Cc: Ard Biesheuvel , Will Deacon , Marc Zyngier , Arnd Bergmann , Greg Kroah-Hartman , Andrew Morton , Linus Torvalds , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, "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 Tue, Apr 12, 2022 at 06:18:46PM +0800, Herbert Xu wrote: > On Tue, Apr 12, 2022 at 11:02:54AM +0100, Catalin Marinas wrote: > > This series does not penalise any architecture. It doesn't even make > > arm64 any worse than it currently is. > > Right, the patch as it stands doesn't change anything. However, > it is also broken as it stands. As I said before, CRYPTO_MINALIGN > is not something that is guaranteed by the Crypto API, it is simply > a statement of whatever kmalloc returns. I agree that CRYPTO_MINALIGN is not guaranteed by the Crypto API. What I'm debating is the intended use for CRYPTO_MINALIGN in some (most?) of the drivers. It's not just about kmalloc() but also a build-time offset of buffers within structures to guarantee DMA safety. This can't be fixed by cra_alignmask. We could leave CRYPTO_MINALIGN as ARCH_KMALLOC_MINALIGN and that matches it being just a statement of the kmalloc() minimum alignment. But since it is also overloaded with the DMA in-structure offset alignment, we'd need a new CRYPTO_DMA_MINALIGN (and _ATTR) to annotate those structures. I have a suspicion there'll be fewer of the original CRYPTO_MINALIGN uses left, hence my approach to making this bigger from the start. There's also Ard's series introducing CRYPTO_REQ_MINALIGN while leaving CRYPT_MINALIGN for DMA-safe offsets (IIUC): https://lore.kernel.org/r/20220406142715.2270256-1-ardb@kernel.org > So if kmalloc is no longer returning CRYPTO_MINALIGN-aligned > memory, then those drivers that need this alignment for DMA > will break anyway. No. As per one of my previous emails, kmalloc() will preserve the DMA alignment for an SoC even if smaller than CRYPTO_MINALIGN (or a new CRYPTO_DMA_MINALIGN). Since kmalloc() returns DMA-safe pointers and CRYPTO_MINALIGN (or a new CRYPTO_DMA_MINALIGN) is DMA-safe, so would an offset from a pointer returned by kmalloc(). > If you want the Crypto API to guarantee alignment over and above > that returned by kmalloc, the correct way is to use cra_alignmask. For kmalloc(), this would work, but for the current CRYPTO_MINALIGN_ATTR uses it won't. Thanks. -- Catalin