Re: [RFC PATCH 1/5] virtio: introduce SUSPEND bit in device status

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

On 8/15/2023 8:37 AM, Jason Wang wrote:
> On Tue, Aug 15, 2023 at 8:26âAM Jason Wang <jasowang@redhat.com> wrote:
> > On Mon, Aug 14, 2023 at 7:29âPM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
> > > This patch introudces a new status bit in the device status: SUSPEND.
> > >
> > > This SUSPEND bit can be used by the driver to suspend a device,
> > > in order to stablize the device states and virtqueue states.
> > >
> > > Its main use case is live migration.
> > I think patch 3 needs to be squashed into this one.
> >
> > > 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 | 18 ++++++++++++++++++
> > >   1 file changed, 18 insertions(+)
> > >
> > > diff --git a/content.tex b/content.tex
> > > index 0a62dce..1bb4401 100644
> > > --- a/content.tex
> > > +++ b/content.tex
> > > @@ -47,6 +47,9 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> > >   \item[DRIVER_OK (4)] Indicates that the driver is set up and ready to
> > >     drive the device.
> > >
> > > +\item[SUSPEND (16)] When VIRTIO_F_SUSPEND is negotiated, indicates that the
> > > +  device has been suspended by the driver.
> > > +
> > >   \item[DEVICE_NEEDS_RESET (64)] Indicates that the device has experienced
> > >     an error from which it can't recover.
> > >   \end{description}
> > > @@ -73,6 +76,10 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> > >   recover by issuing a reset.
> > >   \end{note}
> > >
> > > +The driver MUST NOT set SUSPEND if FEATURES_OK is not set.
> > > +
> > > +When set SUSPEND, the driver MUST re-read \field{device status} to ensure the SUSPEND bit is set.
> > > +
> > >   \devicenormative{\subsection}{Device Status Field}{Basic Facilities of a Virtio Device / Device Status Field}
> > >
> > >   The device MUST NOT consume buffers or send any used buffer
> > > @@ -82,6 +89,13 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> > >   that a reset is needed.  If DRIVER_OK is set, after it sets DEVICE_NEEDS_RESET, the device
> > >   MUST send a device configuration change notification to the driver.
> > >
> > > +The device MUST ignore SUSPEND if FEATURES_OK is not set.
> > Is there any value to allow SUSPEND to be set without DRIVER_OK?
> >
> > > +
> > > +The deivce MUST ignore SUSPEND if VIRTIO_F_SUSPEND is not negotiated.
> > typo.
> >
> > Thanks
> Btw, it's not clear to me if driver is allowed to clear this bit.
To allow terminate a live migration process or resume from a failed live 
migration,
we allow DRIVER_OK to clear SUSPEND, in patch 1.

Thanks
> Thanks
>
> > > +
> > > +If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device MUST clear SUSPEND
> > > +and resumes operation upon DRIVER_OK.
> > > +
> > >   \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature Bits}
> > >
> > >   Each virtio device offers all the features it understands.  During
> > > @@ -872,6 +886,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
> > >          \ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} for
> > >          handling features reserved for future use.
> > >
> > > +  \item[VIRTIO_F_SUSPEND(41)] This feature indicates that the driver can
> > > +   SUSPEND the device.
> > > +   See \ref{sec:Basic Facilities of a Virtio Device / Device Status Field}.
> > > +
> > >   \end{description}
> > >
> > >   \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> > > --
> > > 2.35.3