Re: [virtio-comment] [PATCH v1 1/8] admin: Add theory of operation for device migration

[Jason Wang <jasowang@redhat.com>]

On Wed, Nov 22, 2023 at 3:48âPM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Wed, Nov 22, 2023 at 12:13:34PM +0800, Jason Wang wrote:
> > > > What's wrong if we just allow them to be R/W over adminq/cmmands?
> > > >
> > > As explained before,
> > > Each guest has its own dedicated non mediated interface as defined in virtio spec to not involve hypervisor.
> >
> > So what's wrong with inventing per VF queue to do that? For example
> > transport virtqueue.
>
> Nothing is wrong with this.
>
> But what is problematic is just re-using config space for migration because

It's not a reusing, it works exactly like this proposal:

1) VF config space is assigned to guest
2) using PF queue to migrate

The only difference is the command:

In this proposal, it is

1) virtio_dev_ctx_pci_vq_cfg structure
2) in transport virtqueue, it introduce a set of commands to access
one or several fields on the common cfg

Thanks

> it means we can not just say "don't access device after it is stopped"
> because yes you need to access it to save/restore state.
> And a new interface over admin cmds just for this side-steps the
> issue nicely.
>
> --
> MST
>