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

Xu Zaibo
2018-10-15T08:50:45Z

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

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