Re: Hotplug support for VFIO

[Alejandro Lucero <alejandro.lucero@netronome.com>]

Hi Eelco,

On Wed, Feb 8, 2017 at 9:41 AM, Eelco Chaudron <echaudron@redhat.com> wrote:

> Hi Anatoly,
>
> This will be great... If you want I can do some testing on (early) patches
> if required.
>
> Also do you know why it is currently not supported, i.e. what are the
> limitations?
>
> Thanks,
>

I assume your reply was to my previous email and not to Anatoly's one. My
apologies if this assumption is wrong.
By the way, you did not reply to the list, but I'm doing to do so because
this could be interesting to other people. Also, I'm CCing hotplug UIO
developer, Tetsuya Mukawa, since there is no a specific maintainer for this
functionality.

I think the main problem for supporting VFIO hotplug is to deal with what
VFIO does, this is IOMMU mappings.
There is no code for doing so, and although the implementation would use
most of the code already there for UIO hotplug, which is basically related
to unmapping PCI resources, and the interrupt part will be likely quite
similar, the IOMMU unmapping requires more work.

I dare to say this is the main reason for not having VFIO hotplug support
right now. Maybe Tetsuya can confirm this or give us other reasons.


>
> Eelco
>
>
>
> On 07/02/17 10:29, Alejandro Lucero wrote:
>
> It seems none is working on this VFIO support.
>
> I will work on this if there is no reply to this thread saying the
> opposite the next days.
>
> On Thu, Feb 2, 2017 at 12:58 PM, Eelco Chaudron <echaudron@redhat.com>
> wrote:
>
>> On 02/02/17 13:05, Burakov, Anatoly wrote:
>>
>>> Hi Eelco,
>>>
>>> Please forgive me my ignorance on this matter, but doesn't it work at
>>> the moment? I would assume that if regular PCI hotplug works (with
>>> igb_uio), then so would hotplug with VFIO, as it basically utilizes the
>>> same PCI infrastructure igb_uio does. That said, I'm not aware of any
>>> patches submitted that had to do with VFIO and hotplug, so I guess the
>>> answer is, not at the moment.
>>>
>>> Thanks,
>>> Anatoly
>>>
>> I was asking as the documentation explicitly mentions its not supported.
>> http://dpdk.org/doc/guides/prog_guide/port_hotplug_framework.html#hotplug
>>
>> - "To detach a port, the port should be backed by a device that igb_uio
>> manages. VFIO is not supported."
>>
>> I could not find any specific reason why it's not supported, so if some
>> one can explain this it would help also...
>>
>> Cheers,
>>
>> Eelco
>>
>>
>>
>
>