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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 90DBEC433F5 for ; Tue, 12 Apr 2022 12:31:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 13D766B0082; Tue, 12 Apr 2022 08:31:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0EF2F6B0083; Tue, 12 Apr 2022 08:31:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EF6DC6B0085; Tue, 12 Apr 2022 08:31:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.28]) by kanga.kvack.org (Postfix) with ESMTP id E08426B0082 for ; Tue, 12 Apr 2022 08:31:29 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id A9729620FA for ; Tue, 12 Apr 2022 12:31:29 +0000 (UTC) X-FDA: 79348162698.03.2AFBA34 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf14.hostedemail.com (Postfix) with ESMTP id D6E7F100003 for ; Tue, 12 Apr 2022 12:31:28 +0000 (UTC) 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 1ACFCB81D2E; 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: X-Rspam-User: X-Stat-Signature: zine8eiqq31ataz1afc9kmq6t5bdfimw Authentication-Results: imf14.hostedemail.com; dkim=none; spf=pass (imf14.hostedemail.com: domain of cmarinas@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D6E7F100003 X-HE-Tag: 1649766688-112456 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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