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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 8CA38C433B4 for ; Thu, 15 Apr 2021 21:16:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 56DD7610CB for ; Thu, 15 Apr 2021 21:16:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235710AbhDOVQb (ORCPT ); Thu, 15 Apr 2021 17:16:31 -0400 Received: from mga02.intel.com ([134.134.136.20]:6498 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234959AbhDOVQa (ORCPT ); Thu, 15 Apr 2021 17:16:30 -0400 IronPort-SDR: cOmfhycYgrXXfAL7B4EchOUSG+0UqDMSDnLXPGMBGWF3TFhx/wsqpAY8GZHnz7I2siT99b7dpx GvTIZBCe71TA== X-IronPort-AV: E=McAfee;i="6200,9189,9955"; a="182068864" X-IronPort-AV: E=Sophos;i="5.82,225,1613462400"; d="scan'208";a="182068864" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Apr 2021 14:16:06 -0700 IronPort-SDR: q5op6QHfmrt3NbPHSPNKpJwGJNDmsFZ2z4LhgON7RFerF+9cnD82iJXQadzBHw5/coMOJnqkkU 0cBuTmD4hyYg== X-IronPort-AV: E=Sophos;i="5.82,225,1613462400"; d="scan'208";a="461754208" Received: from jacob-builder.jf.intel.com (HELO jacob-builder) ([10.7.199.155]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Apr 2021 14:16:06 -0700 Date: Thu, 15 Apr 2021 14:18:45 -0700 From: Jacob Pan To: Christoph Hellwig Cc: LKML , iommu@lists.linux-foundation.org, Joerg Roedel , Lu Baolu , Jean-Philippe Brucker , "Tian, Kevin" , Dave Jiang , Raj Ashok , vkoul@kernel.org, Jason Gunthorpe , zhangfei.gao@linaro.org, jacob.jun.pan@linux.intel.com Subject: Re: [PATCH v2 2/2] iommu/sva: Remove mm parameter from SVA bind API Message-ID: <20210415141845.06e5a1cf@jacob-builder> In-Reply-To: <20210415064459.GB1938497@infradead.org> References: <1618414077-28808-1-git-send-email-jacob.jun.pan@linux.intel.com> <1618414077-28808-3-git-send-email-jacob.jun.pan@linux.intel.com> <20210415064459.GB1938497@infradead.org> Organization: OTC X-Mailer: Claws Mail 3.17.5 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Christoph, On Thu, 15 Apr 2021 07:44:59 +0100, Christoph Hellwig wrote: > > * > > * Returns 0 on success and < 0 on error. > > @@ -28,6 +28,9 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm, > > ioasid_t min, ioasid_t max) int ret = 0; > > ioasid_t pasid; > > > > + if (mm != current->mm) > > + return -EINVAL; > > + > > Why not remove the parameter entirely? It was removed in my v1 but thought it would be cleaner if we treat iommu_sva_alloc_pasid() as a leaf function of iommu_sva_bind_device(). Then we don't have to do get_task_mm() every time. But to your point below, it is better to get low-level driver handle it. > > > @@ -2989,8 +2990,11 @@ iommu_sva_bind_device(struct device *dev, struct > > mm_struct *mm, unsigned int fla return ERR_PTR(-ENODEV); > > > > /* Supervisor SVA does not need the current mm */ > > - if ((flags & IOMMU_SVA_BIND_SUPERVISOR) && mm) > > - return ERR_PTR(-EINVAL); > > + if (!(flags & IOMMU_SVA_BIND_SUPERVISOR)) { > > + mm = get_task_mm(current); > > + if (!mm) > > + return ERR_PTR(-EINVAL); > > + } > > I don't see why we need the reference. I think we should just stop > passing the mm to ->sva_bind and let the low-level driver deal with > any reference to current->mm where needed. The mm users reference is just for precaution, in case low level driver use kthread etc. I agree it is cleaner to just remove mm here, let the low-level driver deal with it. Let me give it a spin. Thanks, Jacob