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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 B9636C433B4 for ; Wed, 14 Apr 2021 06:32:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E0D7611EE for ; Wed, 14 Apr 2021 06:32:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347930AbhDNGco (ORCPT ); Wed, 14 Apr 2021 02:32:44 -0400 Received: from mga03.intel.com ([134.134.136.65]:25036 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231831AbhDNGc0 (ORCPT ); Wed, 14 Apr 2021 02:32:26 -0400 IronPort-SDR: XhwycpHN6oHcXIMOs2W5zE7xuKkVZyVdu2kwZ3FMGG+QdG3vNijWAP8+gQa/T80Afb30sKKzh5 KoPxaFjncsIg== X-IronPort-AV: E=McAfee;i="6200,9189,9953"; a="194603677" X-IronPort-AV: E=Sophos;i="5.82,221,1613462400"; d="scan'208";a="194603677" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Apr 2021 23:31:49 -0700 IronPort-SDR: jtTk4WrJ1bqaHDp2OMiOJLdZVz7CpNjV6TV1Sg570t5Pli+ReRHeJNydL3jvtdloMOYZwH7tn6 r2LcAEzJYvOw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.82,221,1613462400"; d="scan'208";a="443703998" Received: from allen-box.sh.intel.com (HELO [10.239.159.128]) ([10.239.159.128]) by fmsmga004.fm.intel.com with ESMTP; 13 Apr 2021 23:31:45 -0700 Cc: baolu.lu@linux.intel.com, LKML , iommu@lists.linux-foundation.org, Joerg Roedel , Jean-Philippe Brucker , Yi Liu , Raj Ashok , "Tian, Kevin" , Jason Gunthorpe , Dave Jiang , wangzhou1@hisilicon.com, zhangfei.gao@linaro.org, vkoul@kernel.org Subject: Re: [PATCH 2/2] iommu/sva: Remove mm parameter from SVA bind API To: Jacob Pan , Jean-Philippe Brucker References: <1617901736-24788-1-git-send-email-jacob.jun.pan@linux.intel.com> <1617901736-24788-2-git-send-email-jacob.jun.pan@linux.intel.com> <20210409110305.6b0471d9@jacob-builder> <20210413170947.35ba9267@jacob-builder> From: Lu Baolu Message-ID: <41433d99-e413-f5bf-5279-695dae6c58ba@linux.intel.com> Date: Wed, 14 Apr 2021 14:22:09 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210413170947.35ba9267@jacob-builder> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jacob, On 4/14/21 8:09 AM, Jacob Pan wrote: > Hi Jean, > > On Fri, 9 Apr 2021 11:03:05 -0700, Jacob Pan > wrote: > >>> problems: >>> >>> * We don't have a use-case for binding the mm of a remote process (and >>> it's supposedly difficult for device drivers to do it securely). So >>> OK, we remove the mm argument from iommu_sva_bind_device() and use the >>> current mm. But the IOMMU driver isn't going to do >>> get_task_mm(current) every time it needs the mm being bound, it will >>> take it from iommu_sva_bind_device(). Likewise iommu_sva_alloc_pasid() >>> shouldn't need to bother with get_task_mm(). >>> >>> * cgroup accounting for IOASIDs needs to be on the current task. >>> Removing the mm parameter from iommu_sva_alloc_pasid() doesn't help >>> with that. Sure it indicates that iommu_sva_alloc_pasid() needs a >>> specific task context but that's only for cgroup purpose, and I'd >>> rather pass the cgroup down from iommu_sva_bind_device() anyway (but am >>> fine with keeping it within ioasid_alloc() for now). Plus it's an >>> internal helper, easy for us to check that the callers are doing the >>> right thing. >> With the above split, we really just have one allocation function: >> ioasid_alloc(), so it can manage current cgroup accounting within. Would >> this work? > After a few attempts, I don't think the split can work better. I will > restore the mm parameter and add a warning if mm != current->mm. I still worry about supervisor pasid allocation. If we use iommu_sva_alloc_pasid() to allocate a supervisor pasid, which mm should the pasid be set? I've ever thought about passing &init_mm to iommu_sva_alloc_pasid(). But if you add "mm != current->mm", this seems not to work. Or do you prefer a separated interface for supervisor pasid allocation/free? Best regards, baolu > > Thanks, > > Jacob >