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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C19BC433FE for ; Thu, 18 Nov 2021 01:17:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3CD5661B62 for ; Thu, 18 Nov 2021 01:17:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242186AbhKRBUT (ORCPT ); Wed, 17 Nov 2021 20:20:19 -0500 Received: from mga07.intel.com ([134.134.136.100]:42317 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242174AbhKRBUP (ORCPT ); Wed, 17 Nov 2021 20:20:15 -0500 X-IronPort-AV: E=McAfee;i="6200,9189,10171"; a="297510643" X-IronPort-AV: E=Sophos;i="5.87,243,1631602800"; d="scan'208";a="297510643" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Nov 2021 17:17:15 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.87,243,1631602800"; d="scan'208";a="495157953" Received: from allen-box.sh.intel.com (HELO [10.239.159.118]) ([10.239.159.118]) by orsmga007.jf.intel.com with ESMTP; 17 Nov 2021 17:17:09 -0800 Cc: baolu.lu@linux.intel.com, Christoph Hellwig , Greg Kroah-Hartman , Joerg Roedel , Alex Williamson , Bjorn Helgaas , Kevin Tian , Ashok Raj , Chaitanya Kulkarni , kvm@vger.kernel.org, rafael@kernel.org, linux-pci@vger.kernel.org, Cornelia Huck , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Jacob jun Pan , Diana Craciun , Will Deacon Subject: Re: [PATCH 01/11] iommu: Add device dma ownership set/release interfaces To: Jason Gunthorpe References: <20211115020552.2378167-1-baolu.lu@linux.intel.com> <20211115020552.2378167-2-baolu.lu@linux.intel.com> <20211116134603.GA2105516@nvidia.com> <20211117133517.GJ2105516@nvidia.com> From: Lu Baolu Message-ID: <5901c54b-a6eb-b060-aa52-15de7708d703@linux.intel.com> Date: Thu, 18 Nov 2021 09:12:41 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20211117133517.GJ2105516@nvidia.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 11/17/21 9:35 PM, Jason Gunthorpe wrote: > On Wed, Nov 17, 2021 at 01:22:19PM +0800, Lu Baolu wrote: >> Hi Jason, >> >> On 11/16/21 9:46 PM, Jason Gunthorpe wrote: >>> On Tue, Nov 16, 2021 at 09:57:30AM +0800, Lu Baolu wrote: >>>> Hi Christoph, >>>> >>>> On 11/15/21 9:14 PM, Christoph Hellwig wrote: >>>>> On Mon, Nov 15, 2021 at 10:05:42AM +0800, Lu Baolu wrote: >>>>>> +enum iommu_dma_owner { >>>>>> + DMA_OWNER_NONE, >>>>>> + DMA_OWNER_KERNEL, >>>>>> + DMA_OWNER_USER, >>>>>> +}; >>>>>> + >>>>> >>>>>> + enum iommu_dma_owner dma_owner; >>>>>> + refcount_t owner_cnt; >>>>>> + struct file *owner_user_file; >>>>> >>>>> I'd just overload the ownership into owner_user_file, >>>>> >>>>> NULL -> no owner >>>>> (struct file *)1UL) -> kernel >>>>> real pointer -> user >>>>> >>>>> Which could simplify a lot of the code dealing with the owner. >>>>> >>>> >>>> Yeah! Sounds reasonable. I will make this in the next version. >>> >>> It would be good to figure out how to make iommu_attach_device() >>> enforce no other driver binding as a kernel user without a file *, as >>> Robin pointed to, before optimizing this. >>> >>> This fixes an existing bug where iommu_attach_device() only checks the >>> group size and is vunerable to a hot plug increasing the group size >>> after it returns. That check should be replaced by this series's logic >>> instead. >> >> As my my understanding, the essence of this problem is that only the >> user owner of the iommu_group could attach an UNMANAGED domain to it. >> If I understand it right, how about introducing a new interface to >> allocate a user managed domain and storing the user file pointer in it. > > For iommu_attach_device() the semantic is simple non-sharing, so there > is no need for the file * at all, it can just be NULL. The file * being NULL means the device is only owned by the kernel driver. Perhaps we can check this pointer in iommu_attach_device() to avoid using it for user domain attachment. > >> Does above help here? > > No, iommu_attach_device() is kernel only and should not interact with > userspace. The existing iommu_attach_device() allows only for singleton group. As we have added group ownership attribute, we can enforce this interface only for kernel domain usage. > > I'm also going to see if I can learn what Tegra is doing with > iommu_attach_group() Okay! Thank you! > > Jason > Best regards, baolu