RE: [virtio-comment] Re: [PATCH 0/2] Selective queue enabling

[Parav Pandit <parav@nvidia.com>]

> From: Zhu, Lingshan <lingshan.zhu@intel.com>
> Sent: Wednesday, June 14, 2023 12:27 AM

> > If a device has assumed that queue_reset must be done after DRIVER_OK
> > stage because until that point the device is not "live", Such device needs the
> fix.
> I think queue_reset just resets the queue and its fields including the
> queue_enable. DRIVER_OK is not a must for performing a queue_reset, My
> understanding is:
> - before DRIVER_OK, the driver can re-config the queue anytime, doesn't need
> a reset_queue

Before DRIVER_OK stage, to reconfigure a queue, driver needs to write queue_enable = 0.
This is not allowed in the spec.
So driver need to use queue_reset to reconfigure.

> - after DRIVER_OK, the driver has to reset the queue to re-config the queue.
> Because a queue is considered alive when both DRIVER_OK && queue_enable,
> and resetting a queue also set queue_enable to zero.
> 
> At the end of the migration, hypervisor should reset the queues and config the
> queues with the guest configurations and enable the queues, right?

The migration for non vdpa world would not require any of the queue enable/disable flow because device is migrated (paused) with its current state.
And it can resume from where it left off.