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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 C768AFA372C for ; Fri, 8 Nov 2019 17:49:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9E61E20673 for ; Fri, 8 Nov 2019 17:49:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730719AbfKHRtR (ORCPT ); Fri, 8 Nov 2019 12:49:17 -0500 Received: from lhrrgout.huawei.com ([185.176.76.210]:2080 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729924AbfKHRtQ (ORCPT ); Fri, 8 Nov 2019 12:49:16 -0500 Received: from LHREML713-CAH.china.huawei.com (unknown [172.18.7.108]) by Forcepoint Email with ESMTP id CEC7F8DD5204AF80FBFE; Fri, 8 Nov 2019 17:49:14 +0000 (GMT) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by LHREML713-CAH.china.huawei.com (10.201.108.36) with Microsoft SMTP Server (TLS) id 14.3.408.0; Fri, 8 Nov 2019 17:49:14 +0000 Received: from [127.0.0.1] (10.202.226.46) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.1713.5; Fri, 8 Nov 2019 17:49:14 +0000 Subject: Re: [PATCH v2 6/9] Revert "iommu/arm-smmu: Make arm-smmu-v3 explicitly non-modular" To: Will Deacon CC: , , "Isaac J. Manjarres" , Jean-Philippe Brucker , Saravana Kannan , "Bjorn Helgaas" , Robin Murphy References: <20191108151608.20932-1-will@kernel.org> <20191108151608.20932-7-will@kernel.org> <06dfd385-1af0-3106-4cc5-6a5b8e864759@huawei.com> <7e906ed1-ab85-7e25-9b29-5497e98da8d8@huawei.com> <20191108164728.GB20866@willie-the-truck> <20191108173248.GA22448@willie-the-truck> From: John Garry Message-ID: <5a7df825-ca69-a2ad-e0b8-94a971528b89@huawei.com> Date: Fri, 8 Nov 2019 17:49:13 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <20191108173248.GA22448@willie-the-truck> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.226.46] X-ClientProxiedBy: lhreml703-chm.china.huawei.com (10.201.108.52) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/11/2019 17:32, Will Deacon wrote: > On Fri, Nov 08, 2019 at 05:25:09PM +0000, John Garry wrote: >> On 08/11/2019 16:47, Will Deacon wrote: >>> On Fri, Nov 08, 2019 at 04:44:25PM +0000, John Garry wrote: >>>> BTW, it now looks like it was your v1 series I was testing there, on your >>>> branch iommu/module. It would be helpful to update for ease of testing. >>> >>> Yes, sorry about that. I'll update it now (although I'm not sure it will >>> help with this -- I was going to see what happens with other devices such >>> as the intel-iommu or storage controllers) >> >> So I tried your v2 series for this - it has the same issue, as I >> anticipated. > > Right, I'm just not sure how resilient drivers are expected to be to force > unbinding like this. You can break lots of stuff with root... For sure, but it is good practice to limit that. I had to fix something like this recently, so know about it... another potential problem is use-after-frees, where your device managed memory is freed at removal but still registered somewhere. > >> It seems that some iommu drivers do call iommu_device_register(), so maybe a >> decent reference. Or simply stop the driver being unbound. > > I'm not sure what you mean about iommu_device_register() (we call that > already), Sorry, I meant to say iommu_device_unregister(). but I guess we can keep the '.suppress_bind_attrs = true' if > necessary. It may be good to add it to older stable kernels also, pre c07b6426df92. I'll have a play on my laptop and see how well that works if > you start unbinding stuff. Cheers, John