On Wed, Jun 1, 2022 at 4:19 AM Parav Pandit <parav at nvidia.com>
wrote:>
>
> > From: Jason Wang <jasowang at redhat.com>
> > Sent: Sunday, May 29, 2022 11:39 PM
> >
> > On Fri, May 27, 2022 at 6:56 PM Michael S. Tsirkin <mst at
redhat.com> wrote:
> > >
> > > On Thu, May 26, 2022 at 12:54:32PM +0000, Parav Pandit wrote:
> > > >
> > > >
> > > > > From: Eugenio P?rez <eperezma at redhat.com>
> > > > > Sent: Thursday, May 26, 2022 8:44 AM
> > > >
> > > > > Implement stop operation for vdpa_sim devices, so
vhost-vdpa will
> > > > > offer
> > > > >
> > > > > that backend feature and userspace can effectively stop
the device.
> > > > >
> > > > >
> > > > >
> > > > > This is a must before get virtqueue indexes (base) for
live
> > > > > migration,
> > > > >
> > > > > since the device could modify them after userland gets
them. There
> > > > > are
> > > > >
> > > > > individual ways to perform that action for some devices
> > > > >
> > > > > (VHOST_NET_SET_BACKEND, VHOST_VSOCK_SET_RUNNING, ...)
but
> > there
> > > > > was no
> > > > >
> > > > > way to perform it for any vhost device (and, in
particular, vhost-vdpa).
> > > > >
> > > > >
> > > > >
> > > > > After the return of ioctl with stop != 0, the device
MUST finish
> > > > > any
> > > > >
> > > > > pending operations like in flight requests. It must
also preserve
> > > > > all
> > > > >
> > > > > the necessary state (the virtqueue vring base plus the
possible
> > > > > device
> > > > >
> > > > > specific states) that is required for restoring in the
future. The
> > > > >
> > > > > device must not change its configuration after that
point.
> > > > >
> > > > >
> > > > >
> > > > > After the return of ioctl with stop == 0, the device
can continue
> > > > >
> > > > > processing buffers as long as typical conditions are
met (vq is
> > > > > enabled,
> > > > >
> > > > > DRIVER_OK status bit is enabled, etc).
> > > >
> > > > Just to be clear, we are adding vdpa level new ioctl() that
doesn?t map to
> > any mechanism in the virtio spec.
> > > >
> > > > Why can't we use this ioctl() to indicate driver to
start/stop the device
> > instead of driving it through the driver_ok?
> > > > This is in the context of other discussion we had in the LM
series.
> > >
> > > If there's something in the spec that does this then
let's use that.
> >
> > Actually, we try to propose a independent feature here:
> >
> > https://lists.oasis-open.org/archives/virtio-dev/202111/msg00020.html
> >
> This will stop the device for all the operations.
Well, the ability to query the virtqueue state was proposed as another
feature (Eugenio, please correct me). This should be sufficient for
making virtio-net to be live migrated.
https://lists.oasis-open.org/archives/virtio-comment/202103/msg00008.html
> Once the device is stopped, its state cannot be queried further as device
won't respond.
> It has limited use case.
> What we need is to stop non admin queue related portion of the device.
See above.
Thanks
>
> > Does it make sense to you?
> >
> > Thanks
> >
> > > Unfortunately the LM series seems to be stuck on moving bits
around
> > > with the admin virtqueue ...
> > >
> > > --
> > > MST
> > >
>