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Subject: Re: [virtio-comment] Live Migration of Virtio Virtual Function



On 8/17/2021 11:51 AM, Jason Wang wrote:

å 2021/8/12 äå8:08, Max Gurtovoy åé:

Hi all,

Live migration is one of the most important features of virtualization and virtio devices are oftenly found in virtual environments.

The migration process is managed by a migration SW that is running on the hypervisor and the VM is not aware of the process at all.

Unlike the vDPA case, a real pci Virtual Function state resides in the HW.


vDPA doesn't prevent you from having HW states. Actually from the view of the VMM(Qemu), it doesn't care whether or not a state is stored in the software or hardware. A well designed VMM should be able to hide the virtio device implementation from the migration layer, that is how Qemu is wrote who doesn't care about whether or not it's a software virtio/vDPA device or not.


In our vision, in order to fulfil the Live migration requirements for virtual functions, each physical function device must implement migration operations. Using these operations, it will be able to master the migration process for the virtual function devices. Each capable physical function device has a supervisor permissions to change the virtual function operational states, save/restore its internal state and start/stop dirty pages tracking.


For "supervisor permissions", is this from the software point of view? Maybe it's better to give an example for this.

A permission to a PF device for quiesce and freeze a VF device for example.



An example of this approach can be seen in the way NVIDIA performs live migration of a ConnectX NIC function:

https://github.com/jgunthorpe/linux/commits/mlx5_vfio_pci <https://github.com/jgunthorpe/linux/commits/mlx5_vfio_pci>

NVIDIAs SNAP technology enables hardware-accelerated software defined PCIe devices. virtio-blk/virtio-net/virtio-fs SNAP used for storage and networking solutions. The host OS/hypervisor uses its standard drivers that are implemented according to a well-known VIRTIO specifications.

In order to implement Live Migration for these virtual function devices, that use a standard drivers as mentioned, the specification should define how HW vendor should build their devices and for SW developers to adjust the drivers.

This will enable specification compliant vendor agnostic solution.

This is exactly how we built the migration driver for ConnectX (internal HW design doc) and I guess that this is the way other vendors work.

For that, I would like to know if the approach of âPF that controls the VF live migration processâ is acceptable by the VIRTIO technical group ?


I'm not sure but I think it's better to start from the general facility for all transports, then develop features for a specific transport.

a general facility for all transports can be a generic admin queue ?



Thanks


Cheers,

-Max.




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