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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 BC7BDC43381 for ; Tue, 26 Feb 2019 12:38:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 93F51217F5 for ; Tue, 26 Feb 2019 12:38:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726721AbfBZMiG (ORCPT ); Tue, 26 Feb 2019 07:38:06 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:4739 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726063AbfBZMiG (ORCPT ); Tue, 26 Feb 2019 07:38:06 -0500 Received: from DGGEMS411-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id B5619BB2F09F9F440D87; Tue, 26 Feb 2019 20:38:02 +0800 (CST) Received: from [127.0.0.1] (10.177.223.23) by DGGEMS411-HUB.china.huawei.com (10.3.19.211) with Microsoft SMTP Server id 14.3.408.0; Tue, 26 Feb 2019 20:37:56 +0800 Subject: Re: [PATCH RFC 1/1] iommu: set the default iommu-dma mode as non-strict To: Jean-Philippe Brucker , Zhen Lei , John Garry , "Robin Murphy" , Will Deacon , "Joerg Roedel" , linux-arm-kernel , iommu , linux-kernel CC: Yunsheng Lin , Linuxarm , "Chengchuanning (Hisi-Turing)" References: <20190131135211.6732-1-thunder.leizhen@huawei.com> <94b9b0c9-1a24-63ba-5abe-5f6d79fed415@arm.com> From: Hanjun Guo Message-ID: Date: Tue, 26 Feb 2019 20:36:14 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <94b9b0c9-1a24-63ba-5abe-5f6d79fed415@arm.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.223.23] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jean, On 2019/1/31 22:55, Jean-Philippe Brucker wrote: > Hi, > > On 31/01/2019 13:52, Zhen Lei wrote: >> Currently, many peripherals are faster than before. For example, the top >> speed of the older netcard is 10Gb/s, and now it's more than 25Gb/s. But >> when iommu page-table mapping enabled, it's hard to reach the top speed >> in strict mode, because of frequently map and unmap operations. In order >> to keep abreast of the times, I think it's better to set non-strict as >> default. > > Most users won't be aware of this relaxation and will have their system > vulnerable to e.g. thunderbolt hotplug. See for example 4.3 Deferred > Invalidation in > http://www.cs.technion.ac.il/users/wwwb/cgi-bin/tr-get.cgi/2018/MSC/MSC-2018-21.pdf > > Why not keep the policy to secure by default, as we do for > iommu.passthrough? And maybe add something similar to > CONFIG_IOMMU_DEFAULT_PASSTRHOUGH? It's easy enough for experts to pass a > command-line argument or change the default config. Sorry for the late reply, it was Chinese new year, and we had a long discussion internally, we are fine to add a Kconfig but not sure OS vendors will set it to default y. OS vendors seems not happy to pass a command-line argument, to be honest, this is our motivation to enable non-strict as default. Hope OS vendors can see this email thread, and give some input here. Thanks Hanjun