RE: [virtio-comment] Re: [PATCH v1 3/8] device-context: Define the device context fields for device migration

[Parav Pandit <parav@nvidia.com>]

> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> Sent: Wednesday, October 18, 2023 12:06 PM
> 
> On 10/18/2023 1:02 PM, Parav Pandit wrote:
> >
> >> From: virtio-comment@lists.oasis-open.org
> >> <virtio-comment@lists.oasis- open.org> On Behalf Of Zhu, Lingshan
> >> Sent: Monday, October 16, 2023 3:18 PM
> >>
> >> On 10/13/2023 7:54 PM, Parav Pandit wrote:
> >>>> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> >>>> Sent: Friday, October 13, 2023 3:14 PM
> >>>>>>>> How do you transfer the ownership?
> >>>>>>> An additional ownership deletgation by a new admin command.
> >>>>>> if you think this can work, do you want to cook a patch to
> >>>>>> implement this before you submitting this live migration series?
> >>>>> I answered this already above.
> >>>> talk is cheap, show me your patch
> >>> Huh. We presented the infrastructure that migrates, 30+ device
> >>> types,
> >> covering device context ideas from Oracle.
> >>> Covering P2P, supporting device_reset, FLR, dirty page tracking.
> >>>
> >>> Please have some respect for other members who covered more ground
> >>> than
> >> your series.
> >>> What more? Apply the same nested concept on the member device as
> >> Michael suggested, it is nested virtualization maintain exact same semantics.
> >>> So a VF is mapped as PF to the L1 guest.
> >>> L1 guest can enable SR-IOV on it, and map one VF to L2 guest.
> >>>
> >>> This nested work can be extended in future, once first level nesting
> >>> is
> >> covered.
> >>>> Answer all questions above, if you think a management VF can work,
> >>>> please show me your patch.
> >>> The idea evolves from technical debate then pointing fingers like
> >>> your
> >> comment.
> >>> I think a positive discussion with Michael and a pointer to the
> >>> paper from
> >> Jason gave a good direction of doing _right_ nesting that follows two
> principles.
> >>> a. efficiency property
> >>> b. equivalence property
> >>>
> >>> (c. resource control is natural already)
> >>>
> >>> Both apply at VMM and at VM level enabling recursive virtualization,
> >>> by
> >> having VF that can act as PF inside the guest.
> >>> [1] https://dl.acm.org/doi/pdf/10.1145/361011.361073
> >> Please just show me your patch resolving these opens, how about start
> >> from defining virito-fs device context and your management VF?
> > As answered, device context infrastructure is done, per device specific device-
> context will be defined incrementally.
> > I will not be including virtio-fs in this series. It will be done incrementally in
> future utilizing the infrastructure build in this series.
> Done? How do you conclude this? You just tell me what is the full set of virito-fs
> device context now and how to migrate them.
> 
> You cant? you refuse or you don't? Do you expect the HW designer to figure out
> by themself?
I wont be able to tell now as I donât think it is necessary for this series.
If one out of 30 devices cannot migrate because of unimaginable amount of complexity has been placed there, may be one will not implement it as member device.

From experience of migratable complex gpu devices, rdma devices (stateful having hundred thousand of stateful QPs), my understanding is complex state of virtio-fs can be defined and migratable.
Mlx5 driver consist of 150,000 lines of code and that device is migratable with complex state.
So I am optimistic that virtio-fs can be migratable too.
It does not have to limited by my limited creativity of 2023.
May be I am wrong, in that case one will not implement passthrough virtio-fs device.