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 X-Spam-Level: X-Spam-Status: No, score=-8.0 required=3.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BF534C43603 for ; Tue, 17 Dec 2019 15:30:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BF2A21582 for ; Tue, 17 Dec 2019 15:30:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728590AbfLQPa5 (ORCPT ); Tue, 17 Dec 2019 10:30:57 -0500 Received: from ns.iliad.fr ([212.27.33.1]:56708 "EHLO ns.iliad.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728331AbfLQPa5 (ORCPT ); Tue, 17 Dec 2019 10:30:57 -0500 Received: from ns.iliad.fr (localhost [127.0.0.1]) by ns.iliad.fr (Postfix) with ESMTP id C170821560; Tue, 17 Dec 2019 16:30:54 +0100 (CET) Received: from [192.168.108.51] (freebox.vlq16.iliad.fr [213.36.7.13]) by ns.iliad.fr (Postfix) with ESMTP id 9CFC02155B; Tue, 17 Dec 2019 16:30:54 +0100 (CET) To: Greg Kroah-Hartman , Rafael Wysocki , LKML Cc: Robin Murphy , Dmitry Torokhov , Alexey Brodkin , Peter Zijlstra , Will Deacon , Russell King , Bjorn Andersson , Tejun Heo , Mark Brown , Linux ARM From: Marc Gonzalez Subject: [RFC PATCH v1] devres: align devres.data strictly only for devm_kmalloc() Message-ID: <74ae22cd-08c1-d846-3e1d-cbc38db87442@free.fr> Date: Tue, 17 Dec 2019 16:30:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Virus-Scanned: ClamAV using ClamSMTP ; ns.iliad.fr ; Tue Dec 17 16:30:54 2019 +0100 (CET) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit a66d972465d15 ("devres: Align data[] to ARCH_KMALLOC_MINALIGN") increased the alignment of devres.data unconditionally. Some platforms have very strict alignment requirements for DMA-safe addresses, e.g. 128 bytes on arm64. There, struct devres amounts to: 3 pointers + pad_to_128 + data + pad_to_256 i.e. ~220 bytes of padding. Let's enforce the alignment only for devm_kmalloc(). Suggested-by: Robin Murphy Signed-off-by: Marc Gonzalez --- I had not been aware that dynamic allocation granularity on arm64 was 128 bytes. This means there's a lot of waste on small allocations. I suppose there's no easy solution, though. --- drivers/base/devres.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/drivers/base/devres.c b/drivers/base/devres.c index 0bbb328bd17f..bf39188613d9 100644 --- a/drivers/base/devres.c +++ b/drivers/base/devres.c @@ -26,14 +26,7 @@ struct devres_node { struct devres { struct devres_node node; - /* - * Some archs want to perform DMA into kmalloc caches - * and need a guaranteed alignment larger than - * the alignment of a 64-bit integer. - * Thus we use ARCH_KMALLOC_MINALIGN here and get exactly the same - * buffer alignment as if it was allocated by plain kmalloc(). - */ - u8 __aligned(ARCH_KMALLOC_MINALIGN) data[]; + u8 data[]; }; struct devres_group { @@ -789,9 +782,16 @@ static void devm_kmalloc_release(struct device *dev, void *res) /* noop */ } +#define DEVM_KMALLOC_PADDING_SIZE \ + (ARCH_KMALLOC_MINALIGN - sizeof(struct devres) % ARCH_KMALLOC_MINALIGN) + static int devm_kmalloc_match(struct device *dev, void *res, void *data) { - return res == data; + /* + * 'res' is dr->data (not DMA-safe) + * 'data' is the hand-aligned address from devm_kmalloc + */ + return res + DEVM_KMALLOC_PADDING_SIZE == data; } /** @@ -811,6 +811,9 @@ void * devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) { struct devres *dr; + /* Add enough padding to provide a DMA-safe address */ + size += DEVM_KMALLOC_PADDING_SIZE; + /* use raw alloc_dr for kmalloc caller tracing */ dr = alloc_dr(devm_kmalloc_release, size, gfp, dev_to_node(dev)); if (unlikely(!dr)) @@ -822,7 +825,7 @@ void * devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) */ set_node_dbginfo(&dr->node, "devm_kzalloc_release", size); devres_add(dev, dr->data); - return dr->data; + return dr->data + DEVM_KMALLOC_PADDING_SIZE; } EXPORT_SYMBOL_GPL(devm_kmalloc); -- 2.17.1