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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 D51A0C169C4 for ; Thu, 31 Jan 2019 14:55:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B24FE20869 for ; Thu, 31 Jan 2019 14:55:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732401AbfAaOze (ORCPT ); Thu, 31 Jan 2019 09:55:34 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:45370 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725796AbfAaOze (ORCPT ); Thu, 31 Jan 2019 09:55:34 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D2A4C80D; Thu, 31 Jan 2019 06:55:33 -0800 (PST) Received: from [10.1.197.2] (ostrya.cambridge.arm.com [10.1.197.2]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2C1B43F59C; Thu, 31 Jan 2019 06:55:32 -0800 (PST) Subject: Re: [PATCH RFC 1/1] iommu: set the default iommu-dma mode as non-strict To: Zhen Lei , John Garry , Robin Murphy , Will Deacon , Joerg Roedel , linux-arm-kernel , iommu , linux-kernel Cc: Yunsheng Lin References: <20190131135211.6732-1-thunder.leizhen@huawei.com> From: Jean-Philippe Brucker Message-ID: <94b9b0c9-1a24-63ba-5abe-5f6d79fed415@arm.com> Date: Thu, 31 Jan 2019 14:55:17 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190131135211.6732-1-thunder.leizhen@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks, Jean > > Below it's our iperf performance data of 25Gb netcard: > strict mode: 18-20 Gb/s > non-strict mode: 23.5 Gb/s > > Signed-off-by: Zhen Lei > --- > Documentation/admin-guide/kernel-parameters.txt | 4 ++-- > drivers/iommu/iommu.c | 2 +- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index b799bcf..667221f 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -1779,13 +1779,13 @@ > > iommu.strict= [ARM64] Configure TLB invalidation behaviour > Format: { "0" | "1" } > - 0 - Lazy mode. > + 0 - Lazy mode (default). > Request that DMA unmap operations use deferred > invalidation of hardware TLBs, for increased > throughput at the cost of reduced device isolation. > Will fall back to strict mode if not supported by > the relevant IOMMU driver. > - 1 - Strict mode (default). > + 1 - Strict mode. > DMA unmap operations invalidate IOMMU hardware TLBs > synchronously. > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 3ed4db3..10e0b49 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -43,7 +43,7 @@ > #else > static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA; > #endif > -static bool iommu_dma_strict __read_mostly = true; > +static bool iommu_dma_strict __read_mostly; > > struct iommu_callback_data { > const struct iommu_ops *ops; > -- > 1.8.3 > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >