From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xu Zaibo Subject: Re: [PATCH v3 0/8] vfio/mdev: IOMMU aware mediated device Date: Wed, 17 Oct 2018 10:02:24 +0800 Message-ID: <5BC69830.707@huawei.com> References: <20181012051632.26064-1-baolu.lu@linux.intel.com> <5BC1AC09.1060507@huawei.com> <5BC454DF.6010109@huawei.com> <40fc685e-a0be-5e54-2de7-6cd87c36dd80@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <40fc685e-a0be-5e54-2de7-6cd87c36dd80@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Lu Baolu , Joerg Roedel , David Woodhouse , Alex Williamson , Kirti Wankhede Cc: kevin.tian@intel.com, ashok.raj@intel.com, tiwei.bie@intel.com, Jean-Philippe Brucker , sanjay.k.kumar@intel.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, yi.y.sun@intel.com, jacob.jun.pan@intel.com, kvm@vger.kernel.org List-Id: iommu@lists.linux-foundation.org Hi, On 2018/10/16 9:21, Lu Baolu wrote: > Hi, > > On 10/15/2018 04:50 PM, Xu Zaibo wrote: >> Hi, >> >> On 2018/10/15 10:48, Lu Baolu wrote: >>> Hi, >>> >>> On 10/13/2018 04:25 PM, Xu Zaibo wrote: >>>> Hi, >>>> >>>> On 2018/10/12 13:16, Lu Baolu wrote: >>>>> Hi, >>>>> >>>>> The Mediate Device is a framework for fine-grained physical device >>>>> sharing across the isolated domains. Currently the mdev framework >>>>> is designed to be independent of the platform IOMMU support. As the >>>>> result, the DMA isolation relies on the mdev parent device in a >>>>> vendor specific way. >>>>> >>>>> There are several cases where a mediated device could be protected >>>>> and isolated by the platform IOMMU. For example, Intel vt-d rev3.0 >>>>> [1] introduces a new translation mode called 'scalable mode', which >>>>> enables PASID-granular translations. The vt-d scalable mode is the >>>>> key ingredient for Scalable I/O Virtualization [2] [3] which allows >>>>> sharing a device in minimal possible granularity (ADI - Assignable >>>>> Device Interface). >>>>> >>>>> A mediated device backed by an ADI could be protected and isolated >>>>> by the IOMMU since 1) the parent device supports tagging an unique >>>>> PASID to all DMA traffic out of the mediated device; and 2) the DMA >>>>> translation unit (IOMMU) supports the PASID granular translation. >>>>> We can apply IOMMU protection and isolation to this kind of devices >>>>> just as what we are doing with an assignable PCI device. >>>>> >>>>> In order to distinguish the IOMMU-capable mediated devices from those >>>>> which still need to rely on parent devices, this patch set adds two >>>>> new members in struct mdev_device. >>>>> >>>>> * iommu_device >>>>> - This, if set, indicates that the mediated device could >>>>> be fully isolated and protected by IOMMU via attaching >>>>> an iommu domain to this device. If empty, it indicates >>>>> using vendor defined isolation. >>>>> >>>>> * iommu_domain >>>>> - This is a place holder for an iommu domain. A domain >>>>> could be store here for later use once it has been >>>>> attached to the iommu_device of this mdev. >>>>> >>>>> Below helpers are added to set and get above iommu device >>>>> and iommu domain pointers in mdev core implementation. >>>>> >>>>> * mdev_set/get_iommu_device(dev, iommu_device) >>>>> - Set or get the iommu device which represents this mdev >>>>> in IOMMU's device scope. Drivers don't need to set the >>>>> iommu device if it uses vendor defined isolation. >>>>> >>>>> * mdev_set/get_iommu_domain(domain) >>>>> - A iommu domain which has been attached to the iommu >>>>> device in order to protect and isolate the mediated >>>>> device will be kept in the mdev data structure and >>>>> could be retrieved later. >>>>> >>>>> The mdev parent device driver could opt-in that the mdev could be >>>>> fully isolated and protected by the IOMMU when the mdev is being >>>>> created by invoking mdev_set_iommu_device() in its @create(). >>>> I just cannot understand here, how to get an iommu_device while I >>>> create mediated >>>> device in my parent device driver? >>> >>> When you are creating an mdev in your parent driver, you should know >>> which PCI device this mdev belonging to. >>> >> >> So, generally, I can set the parent device as mdev's iommu_device? >> If that, however, Mdev already holds its parent device. So, I just >> figure what >> differences between Mdev's parent device and iommu_device are. >>>> >>>> And why not reuse the device of MDEV instread of adding a new >>>> device here? >>> >>> iommu_device in the mdev_device structure represents the PCI device >>> that represents this mdev in iommu's device scope. IOMMU is only aware >>> of pci devices, it's not aware of mdev device. >> >> Could I understand like that: IOMMU can be aware of the parent device >> of Mdev? >> And more, I am doubting the necessary of iommu_device in Mdev. >> > > The "mdev parent device" and "mdev iommu device" are different although > they might be the same in practice. "mdev parent device" represents the > device who created the mdev. "mdev iommu device" represents the device > who shares the device context entry in iommu tables. > > "mdev iommu device" is always a PCI/PCIe device since IOMMU always use > source id (bus:dev:func) to walk the device context table. But there is > no limitation on who can create an mdev, right? > Actually, I am not sure. My understanding: The DMA address will be issued by the parent device with PASID or something like that to IOMMU facilities. However, the translation units such as iommu （PASID/page .etx）tables are from another device node. I cannot figure out how to control this in hardware level, or whether there will be conflicts between the DMA transation of iommu_device and parent device. Thanks, Zaibo .