Re: [virtio-comment] Re: [RFC PATCH 4/5] virtqueue: constraints for virtqueue state

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 8/17/2023 4:31 PM, Uminski, Piotr wrote:
> > -----Original Message-----
> > From: virtio-comment@lists.oasis-open.org <virtio-comment@lists.oasis-
> > open.org> On Behalf Of Zhu, Lingshan
> > Sent: Tuesday, August 15, 2023 1:30 PM
> > To: Jason Wang <jasowang@redhat.com>
> > Cc: mst@redhat.com; eperezma@redhat.com; cohuck@redhat.com; virtio-
> > comment@lists.oasis-open.org; virtio-dev@lists.oasis-open.org
> > Subject: [virtio-comment] Re: [RFC PATCH 4/5] virtqueue: constraints for
> > virtqueue state
> >
> >
> >
> > On 8/15/2023 8:34 AM, Jason Wang wrote:
> > > On Mon, Aug 14, 2023 at 7:29âPM Zhu Lingshan <lingshan.zhu@intel.com>
> > wrote:
> > > > This commit specifies the constraints of the virtqueue state,
> > > > and the actions should be taken by the device when SUSPEND
> > > > and DRIVER_OK is set
> > > >
> > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > > Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> > > > ---
> > > >    content.tex | 31 +++++++++++++++++++++++++++++++
> > > >    1 file changed, 31 insertions(+)
> > > >
> > > > diff --git a/content.tex b/content.tex
> > > > index 43bd5de..f6ac581 100644
> > > > --- a/content.tex
> > > > +++ b/content.tex
> > > > @@ -587,6 +587,37 @@ \subsection{\field{Used State} Field}
> > > >
> > > >    See also \ref{sec:Packed Virtqueues / Driver and Device Ring Wrap
> > Counters}.
> > > > +\drivernormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio
> > Device / Virtqueue State}
> > > > +
> > > > +If VIRTIO_F_QUEUE_STATE has been negotiated, the driver MUST set
> > SUSPEND in \field{device status}
> > > > +first before getting or setting Virtqueue State of any virtqueues.
> > > I don't get why this is a must. It could be useful for debugging.
> > To avoid race conditions with the device and make the device
> > implementation easier
> It should be possible to set Virtqueue State in two states:
>   - Before DRIVER_OK - as a part of the queue creation at target system
> -  After SUSPEND - when the device was activated and then suspended
> Setting state on active device can produce random results and should be forbidden.
> We may allow to get Virtqueue State on active device, without SUSPEND. However, we should not mandate the device
> to report correct value - on some implementations it may be impossible without suspend.
I agree
> > > > +
> > > > +If VIRTIO_F_QUEUE_STATE has been negotiaged but
> > VIRTIO_RING_F_PACKED not been negotiated,
> > > typo
> > yes
> > > > +the driver MUST NOT access \field{Used State} of any virtqueues, it should
> > use the
> > > > +used index in the used ring.
> > > > +
> > > > +\devicenormative{\subsection}{Virtqueue State}{Basic Facilities of a Virtio
> > Device / Virtqueue State}
> > > > +
> > > > +If VIRTIO_F_QUEUE_STATE has been negotiated but SUSPEND is not set in
> > \field{device status},
> > > > +the device MUST ignore any accesses against Virtqueue State of any
> > virtqueues.
> > > Btw, do we need to clarify the behavior of ring reset after suspending?
> > I think once suspended, the device should ignore resetting a queue
> > > > +
> > > > +When VIRTIO_F_QUEUE_STATE has been negotiated but
> > VIRTIO_RING_F_PACKED is not,
> > > > +the device MUST ignore any accesses against \field{Used State}.
> > > > +
> > > > +If VIRTIO_F_QUEUE_STATE has been negotiaged, the device MUST reset
> > > > +the Virtqueue State of every virtqueue upon a reset.
> > > Need to define the meaning of "reset" this is important for packed virtqueue.
> > I will remove this as Stefan suggested.
> > > > +
> > > > +If VIRTIO_F_QUEUE_STATE and VIRTIO_RING_F_PACKED have been
> > negotiaged, when SUSPEND is set,
> > > > +the device MUST record the Virtqueue State of every enabled virtqueue
> > > > +in \field{Available State} and \field{Used State} respectively,
> > > > +and correspondingly restore the Virtqueue State of every enabled virtqueue
> > > > +from \field{Avaiable State} and \field{Used State} when DRIVER_OK is set.
> > > We can just let the device report those states in any case then we
> > > don't need to care about those details, or did you see any blockers?
> > Agree, I will add the definition of used_state of splitted vq in the
> > next version
> >
> > Thanks
> > > Thanks
> > >
> > > > +
> > > > +If VIRTIO_F_QUEUE_STATE has been negotiated but
> > VIRTIO_RING_F_PACKED has been not, when SUSPEND is set,
> > > > +the device MUST record the available state of every enabled virtqueue in
> > \field{Available State},
> > > > +and restore the available state of every enabled virtqueue from
> > \field{Avaiable State}
> > > > +when DRIVER_OK is set.
> > > > +
> > > >    \input{admin.tex}
> > > >
> > > >    \chapter{General Initialization And Device Operation}\label{sec:General
> > Initialization And Device Operation}
> > > > --
> > > > 2.35.3
> >
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