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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6B72DC48297 for ; Mon, 12 Feb 2024 09:24:19 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rZSXu-00041Y-RH; Mon, 12 Feb 2024 04:24:14 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rZSXt-00041L-W0 for qemu-devel@nongnu.org; Mon, 12 Feb 2024 04:24:14 -0500 Received: from frasgout.his.huawei.com ([185.176.79.56]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rZSXs-0005V0-IP for qemu-devel@nongnu.org; Mon, 12 Feb 2024 04:24:13 -0500 Received: from mail.maildlp.com (unknown [172.18.186.216]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4TYJp83F6Dz6J9p9; Mon, 12 Feb 2024 17:20:16 +0800 (CST) Received: from lhrpeml500005.china.huawei.com (unknown [7.191.163.240]) by mail.maildlp.com (Postfix) with ESMTPS id DD777140CB9; Mon, 12 Feb 2024 17:24:09 +0800 (CST) Received: from localhost (10.202.227.76) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.35; Mon, 12 Feb 2024 09:24:09 +0000 Date: Mon, 12 Feb 2024 09:24:09 +0000 To: Mattias Nissler CC: , , , , Marcel Apfelbaum , Philippe =?ISO-8859-1?Q?Mathieu-Daud=E9?= , , David Hildenbrand , Paolo Bonzini , "Michael S. Tsirkin" , "Richard Henderson" , Elena Ufimtseva Subject: Re: [PATCH v7 2/5] softmmu: Support concurrent bounce buffers Message-ID: <20240212092409.00007dd4@Huawei.com> In-Reply-To: <20240212080617.2559498-3-mnissler@rivosinc.com> References: <20240212080617.2559498-1-mnissler@rivosinc.com> <20240212080617.2559498-3-mnissler@rivosinc.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.227.76] X-ClientProxiedBy: lhrpeml500005.china.huawei.com (7.191.163.240) To lhrpeml500005.china.huawei.com (7.191.163.240) Received-SPF: pass client-ip=185.176.79.56; envelope-from=jonathan.cameron@huawei.com; helo=frasgout.his.huawei.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-to: Jonathan Cameron From: Jonathan Cameron via Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, 12 Feb 2024 00:06:14 -0800 Mattias Nissler wrote: > When DMA memory can't be directly accessed, as is the case when > running the device model in a separate process without shareable DMA > file descriptors, bounce buffering is used. > > It is not uncommon for device models to request mapping of several DMA > regions at the same time. Examples include: > * net devices, e.g. when transmitting a packet that is split across > several TX descriptors (observed with igb) > * USB host controllers, when handling a packet with multiple data TRBs > (observed with xhci) > > Previously, qemu only provided a single bounce buffer per AddressSpace > and would fail DMA map requests while the buffer was already in use. In > turn, this would cause DMA failures that ultimately manifest as hardware > errors from the guest perspective. > > This change allocates DMA bounce buffers dynamically instead of > supporting only a single buffer. Thus, multiple DMA mappings work > correctly also when RAM can't be mmap()-ed. > > The total bounce buffer allocation size is limited individually for each > AddressSpace. The default limit is 4096 bytes, matching the previous > maximum buffer size. A new x-max-bounce-buffer-size parameter is > provided to configure the limit for PCI devices. > > Signed-off-by: Mattias Nissler Tested-by: Jonathan Cameron