Re: [virtio-comment] [RFC PATCH 3/5] virtio: The actions by the device upon SUSPEND

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

On 8/14/2023 11:00 PM, Stefan Hajnoczi wrote:
> On Tue, Aug 15, 2023 at 03:29:02AM +0800, Zhu Lingshan wrote:
> > This commit specifies the actions to be taken by the device upon
> > SUSPEND.
> >
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > Signed-off-by: Eugenio PÃrez <eperezma@redhat.com>
> > Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> > ---
> >   content.tex | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> >
> > diff --git a/content.tex b/content.tex
> > index 074f43e..43bd5de 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -96,6 +96,15 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> >   If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device MUST clear SUSPEND
> >   and resumes operation upon DRIVER_OK.
> >   
> > +If VIRTIO_F_SUSPEND is negotiated, when SUSPEND is set, the device MUST perform the following operations:
> "when SUSPEND is set" is ambigious. It could mean when the driver writes
> the Device Status Field, when the device transitions to SUSPEND, or
> something else. Maybe "before the device reports the SUSPEND bit set in
> the Device Status Field"?
Nice catch! will fix: when the driver sets SUSPEND, before the device 
reports the
SUSPEND bit set in the \field{device status}, the device MUST perform the
following actions.
> > +\begin{itemize}
> > +\item Stop comsuming any descriptors
> "consuming"
yes
> It may be more consistent to talk about virtqueue buffers (i.e.
> requests) rather than descriptors here.
yes
> > +\item Mark all finished descriptors as used and send used buffer notification to the driver
> The device has to complete everything that is in flight, just completing
> "finished" stuff is not enough. Does "finished descriptors" really mean
> "in-flight virtqueue buffers"?
A patch of tracking in-flight descriptors is planned. Here I expect
"finished" mean "done" buffers, transmitted and received ACK.
> "send a used buffer notification" or "send used buffer notifications"
Yes will fix
> > +\item Record Virtqueue State of each enabled virtqueue, see section \ref{sec:Virtqueues / Virtqueue State}
> Does "Record" mean that Virtqueue State fields can only be accessed by
> the driver while device is paused (they may be outdated or invalid while
> the device is unpaused)?
Yes, to avoid race with the device and make device implementation 
easier, this is also mentioned in Patch 4.
> > +\item Pause its operation and preserve all configurations in its Device Configuration Space, see \ref{sec:Basic Facilities of a Virtio Device / Device Configuration Space}
> What does "preserve" mean? Does it mean the Device Configuration Space
> is not allowed to change during SUSPEND?
Yes, once the device presents SUSPEND in its device status, it should 
not change any
fields in its Device Configuration Space.

Thanks for your review
> > +\item Present SUSPEND in \field{device status}
> > +\end{itemize}
> > +
> >   \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature Bits}
> >   
> >   Each virtio device offers all the features it understands.  During
> > --
> > 2.35.3
> >
> >
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