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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 D5E7BC2BB48 for ; Thu, 17 Dec 2020 11:07:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 93BD82389E for ; Thu, 17 Dec 2020 11:07:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727902AbgLQLHa (ORCPT ); Thu, 17 Dec 2020 06:07:30 -0500 Received: from mx2.suse.de ([195.135.220.15]:49704 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726354AbgLQLH3 (ORCPT ); Thu, 17 Dec 2020 06:07:29 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 521EFAC7B; Thu, 17 Dec 2020 11:06:47 +0000 (UTC) Date: Thu, 17 Dec 2020 12:06:47 +0100 Message-ID: From: Takashi Iwai To: Lars-Peter Clausen Cc: alsa-devel@alsa-project.org, gustavoars@kernel.org, linux-kernel@vger.kernel.org, shengjiu.wang@nxp.com, pierre-louis.bossart@linux.intel.com, tiwai@suse.com, xiang@kernel.org, Robin Gong , akpm@linux-foundation.org Subject: Re: [PATCH v1 ] ALSA: core: memalloc: add page alignment for iram In-Reply-To: <70074f62-954a-9b40-ab4a-cb438925060c@metafoo.de> References: <1608221747-3474-1-git-send-email-yibin.gong@nxp.com> <05c824e5-0c33-4182-26fa-b116a42b10d6@metafoo.de> <70074f62-954a-9b40-ab4a-cb438925060c@metafoo.de> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 17 Dec 2020 11:59:23 +0100, Lars-Peter Clausen wrote: > > On 12/17/20 10:55 AM, Takashi Iwai wrote: > > On Thu, 17 Dec 2020 10:43:45 +0100, > > Lars-Peter Clausen wrote: > >> On 12/17/20 5:15 PM, Robin Gong wrote: > >>> Since mmap for userspace is based on page alignment, add page alignment > >>> for iram alloc from pool, otherwise, some good data located in the same > >>> page of dmab->area maybe touched wrongly by userspace like pulseaudio. > >>> > >> I wonder, do we also have to align size to be a multiple of PAGE_SIZE > >> to avoid leaking unrelated data? > > Hm, a good question. Basically the PCM buffer size itself shouldn't > > be influenced by that (i.e. no hw-constraint or such is needed), but > > the padding should be cleared indeed. I somehow left those to the > > allocator side, but maybe it's safer to clear the whole buffer in > > sound/core/memalloc.c commonly. > > What I meant was that most of the APIs that we use to allocate memory > work on a PAGE_SIZE granularity. I.e. if you request a buffer that > where the size is not a multiple of PAGE_SIZE internally they will > still allocate a buffer that is a multiple of PAGE_SIZE and mark the > unused bytes as reserved. > > But I believe that is not the case gen_pool_dma_alloc(). It will > happily allocate those extra bytes to some other allocation request. > > That we need to zero out the reserved bytes even for those other APIs > is a very good additional point! > > I looked at this a few years ago and I'm pretty sure that we cleared > out the allocated area, but I can't find that anymore in the current > code. Which is not so great I guess. IIRC, we used GFP_ZERO in the past for the normal page allocations, but this was dropped as it's no longer supported or so. Also, we clear out the PCM buffer in hw_params call, but this is for the requested size, not the actual allocated size, hence the padding bytes will remain uncleared. So I believe it's safer to add an extra memset() like my test patch. Takashi