[virtio-dev] [PATCH 2/5] virtio: introduce SUSPEND bit in device status

Zhu Lingshan
2023-09-06T08:17:12Z

This patch introduces 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 stabilize the device states and virtqueue states.

Its main use case is live migration.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
content.tex | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

diff --git a/content.tex b/content.tex
index 0e492cd..0fab537 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 SHOULD NOT set SUSPEND if FEATURES_OK is not set.
+
+When setting 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 +89,26 @@ \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.
+
+The device MUST ignore SUSPEND if VIRTIO_F_SUSPEND is not negotiated.
+
+The device SHOULD allow settings to \field{device status} even when SUSPEND is set.
+
+If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device SHOULD clear SUSPEND
+and resumes operation upon DRIVER_OK.
+
+If VIRTIO_F_SUSPEND is negotiated, when the driver sets SUSPEND,
+the device SHOULD perform the following actions before presenting SUSPEND bit in the \field{device status}:
+
+\begin{itemize}
+\item Stop consuming buffers of any virtqueues and mark all finished descritors as used.
+\item Wait until all descriptors that being processed to finish and mark them as used.
+\item Flush all used buffer and send used buffer notifications to the driver.
+\item Record Virtqueue State of each enabled virtqueue, see section \ref{sec:Virtqueues / Virtqueue State}
+\item Pause its operation except \field{device status} and preserve configurations in its Device Configuration Space, see \ref{sec:Basic Facilities of a Virtio Device / Device Configuration Space}
+\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
@@ -937,6 +964,10 @@ \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(42)] 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