linux-kernel - Re: [PATCH v3 0/8] vfio/mdev: IOMMU aware mediated device

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Message-ID: <5BC454DF.6010109@huawei.com>
Date:   Mon, 15 Oct 2018 16:50:39 +0800
From:   Xu Zaibo <xuzaibo@...wei.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>
CC:     <kevin.tian@...el.com>, <ashok.raj@...el.com>,
        <tiwei.bie@...el.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        <sanjay.k.kumar@...el.com>, <iommu@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <yi.y.sun@...el.com>,
        <jacob.jun.pan@...el.com>, <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 0/8] vfio/mdev: IOMMU aware mediated device

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.

Thanks,
Zaibo

.