Re: [PATCH v2 13/40] vfio: Add support for Shared Virtual Addressing

Xu Zaibo
2018-09-06T07:26:40Z

On 2018/9/5 19:02, Jean-Philippe Brucker wrote:
> On 05/09/2018 04:15, Xu Zaibo wrote:
>>>> 1. While the series are finished well, VFIO-PCI device can be held
>>>> by only one process
>>>> through binding IOCTL command without PASID (without PASID
>>>> being exposed user space).
>>> It could, but isn't supported at the moment. In addition to adding
>>> support in the I/O page fault code, we'd also need to update the VFIO
>>> API. Currently a VFIO_TYPE1 domain always supports the MAP/UNMAP ioctl.
>>> The case you describe isn't compatible with MAP/UNMAP, since the process
>>> manages the shared address space with mmap or malloc. We'd probably need
>>> to introduce a new VFIO IOMMU type, in which case the bind could be
>>> performed implicitly when the process does VFIO_SET_IOMMU. Then the
>>> process wouldn't need to send an additional BIND IOCTL.
>> ok. got it. This is the legacy mode, so all the VFIO APIs are kept
>> unchanged?
> Yes, existing VFIO semantics are preserved
>
>>>> 2. While using VFIO-PCI device to support multiple processes with
>>>> SVA series, a primary
>>>> process with multiple secondary processes must be deployed just
>>>> like DPDK(https://www.dpdk.org/).
>>>> And, the PASID still has to be exposed to user land.
>>> Right. A third case, also implemented by this patch (and complete), is
>>> the primary process simply doing a BIND for itself, and using the
>>> returned PASID to share its own address space with the device.
>>>
>> ok. But I am worried that the sulotion of one primary processes with
>> several secondary ones
>>
>> is a little bit limited. Maybe, users don't want to depend on the
>> primary process. :)
> I don't see a better way for vfio-pci, though. But more importantly, I
> don't know of any users :) While the feature is great for testing new
> hardware, and I've been using it for all kinds of stress testing, I
> haven't received feedback from possible users in production settings
> (DPDK etc) and can't speculate about what they'd prefer.
>
At present, It seems no other way existing while being compatible with
current logic.
Thank you.

Thanks,
Zaibo