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 4857FC433F5 for ; Thu, 7 Apr 2022 11:06:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AAC956B0071; Thu, 7 Apr 2022 07:06:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A5B786B0073; Thu, 7 Apr 2022 07:06:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 923476B0074; Thu, 7 Apr 2022 07:06:28 -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 823F36B0071 for ; Thu, 7 Apr 2022 07:06:28 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay11.hostedemail.com (Postfix) with ESMTP id 5C8008269E for ; Thu, 7 Apr 2022 11:06:18 +0000 (UTC) X-FDA: 79329804036.03.A8A6A40 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf15.hostedemail.com (Postfix) with ESMTP id C6229A000B for ; Thu, 7 Apr 2022 11:06:17 +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 dfw.source.kernel.org (Postfix) with ESMTPS id E463A61E24; Thu, 7 Apr 2022 11:06:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8100C385A0; Thu, 7 Apr 2022 11:06:13 +0000 (UTC) Date: Thu, 7 Apr 2022 12:06:10 +0100 From: Catalin Marinas To: Muchun Song Cc: Will Deacon , Marc Zyngier , Arnd Bergmann , Greg Kroah-Hartman , Andrew Morton , Linus Torvalds , Linux Memory Management List , LAK , LKML , Herbert Xu , "David S. Miller" Subject: Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN Message-ID: References: <20220405135758.774016-1-catalin.marinas@arm.com> <20220405135758.774016-8-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C6229A000B X-Stat-Signature: zce1ozbj3tgyy5bdzehxpx3a9w4jtpgk X-Rspam-User: Authentication-Results: imf15.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none); spf=pass (imf15.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org X-HE-Tag: 1649329577-928744 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 Thu, Apr 07, 2022 at 06:00:10PM +0800, Muchun Song wrote: > On Thu, Apr 7, 2022 at 5:25 PM Catalin Marinas wrote: > > On Thu, Apr 07, 2022 at 02:14:15PM +0800, Muchun Song wrote: > > > On Tue, Apr 05, 2022 at 02:57:55PM +0100, Catalin Marinas wrote: > > > > ARCH_DMA_MINALIGN represents the minimum (static) alignment for safe DMA > > > > operations while ARCH_KMALLOC_MINALIGN is the minimum kmalloc() objects > > > > alignment. > > > > > > > > Signed-off-by: Catalin Marinas > > > > Cc: Herbert Xu > > > > Cc: "David S. Miller" > > > > --- > > > > include/linux/crypto.h | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/include/linux/crypto.h b/include/linux/crypto.h > > > > index 2324ab6f1846..654b9c355575 100644 > > > > --- a/include/linux/crypto.h > > > > +++ b/include/linux/crypto.h > > > > @@ -167,7 +167,7 @@ > > > > * maintenance for non-coherent DMA (cache invalidation in particular) does not > > > > * affect data that may be accessed by the CPU concurrently. > > > > */ > > > > -#define CRYPTO_MINALIGN ARCH_KMALLOC_MINALIGN > > > > +#define CRYPTO_MINALIGN ARCH_DMA_MINALIGN > > > > > > I don't think this should be changed since ARCH_KMALLOC_MINALIGN is > > > already aligned with the size what you need. > > > > With this series, ARCH_KMALLOC_MINALIGN is no longer safe for > > non-coherent DMA on all arm64 SoCs, that's what ARCH_DMA_MINALIGN will > > cover. > > > > Now, looking at the comment for CRYPTO_MINALIGN, one aspect it covers is > > the minimum alignment required by C for the crypto_tfm structure access. > > So a smaller ARCH_KMALLOC_MINALIGN would do. But the other part of the > > comment mentions in-structure alignment for non-coherent DMA. Here we'd > > need the upper bound alignment, ARCH_DMA_MINALIGN. > > > > I'll follow up on Herbert's email as I think he has a good point on > > structure vs kmalloc() alignment. > > Got it. Now I know what you want to do. You want to set > ARCH_KMALLOC_MINALIGN to 64, however, the smallest > size of kmem_cache depends on the cache line size at > runtime. But we have to know the safe alignment at building > time. So we have to make those align with ARCH_DMA_MINALIGN. > Right? Right. > I think you are on the right road since most CPUs have a 64-byte cache > line. Yeah, apart from about three SoCs with 128, the rest use 64-byte cache lines. Longer term we should try reduce such alignment below the cache line size *if* the SoC fully DMA-coherent (like x86). In that case cache maintenance for DMA doesn't exist, so there's no risk to smaller allocations. Of course, one can use a kmem_cache_create() with SLAB_HWCACHE_ALIGN and get the cacheline alignment for performance reasons. -- Catalin