[virtio-dev] [PATCH v6 1/1] content: Add new feature VIRTIO_F_PRESERVE_RESOURCES

[Jiqian Chen <Jiqian.Chen@amd.com>]

In some scenes, Qemu may reset or destroy resources of virtio device,
but some of them can't be re-created, so that causes some problems.

For example, when we do S3 for guest, guest will set device_status to
0, it causes Qemu to reset virtioi-gpu device, and then all render
resources of virtio-gpu will be destroyed. As a result, after guest
resuming, the display can't come back, and we only see a black screen.

In order to deal with the above scene, we need a mechanism that allows
guest and Qemu to negotiate their behaviors for resources. So, this
patch adds a new feature named VIRTIO_F_PRESERVE_RESOURCES. It allows
guest to tell Qemu when there is a need to preserve resources, guest
must preserve resources until 0 is set.

Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
---
 conformance.tex   |  2 ++
 content.tex       | 25 +++++++++++++++++++++++++
 transport-pci.tex |  6 ++++++
 3 files changed, 33 insertions(+)

diff --git a/conformance.tex b/conformance.tex
index dc00e84..60cc0b1 100644
--- a/conformance.tex
+++ b/conformance.tex
@@ -91,6 +91,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
 \item \ref{drivernormative:Basic Facilities of a Virtio Device / Packed Virtqueues / The Virtqueue Descriptor Table / Indirect Descriptors}
 \item \ref{drivernormative:Basic Facilities of a Virtio Device / Packed Virtqueues / Supplying Buffers to The Device / Updating flags}
 \item \ref{drivernormative:Basic Facilities of a Virtio Device / Packed Virtqueues / Supplying Buffers to The Device / Sending Available Buffer Notifications}
+\item \ref{drivernormative:Basic Facilities of a Virtio Device / Preserve Resources}
 \item \ref{drivernormative:General Initialization And Device Operation / Device Initialization}
 \item \ref{drivernormative:General Initialization And Device Operation / Device Cleanup}
 \item \ref{drivernormative:Reserved Feature Bits}
@@ -172,6 +173,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
 \item \ref{devicenormative:Basic Facilities of a Virtio Device / Packed Virtqueues / The Virtqueue Descriptor Table}
 \item \ref{devicenormative:Basic Facilities of a Virtio Device / Packed Virtqueues / Scatter-Gather Support}
 \item \ref{devicenormative:Basic Facilities of a Virtio Device / Shared Memory Regions}
+\item \ref{devicenormative:Basic Facilities of a Virtio Device / Preserve Resources}
 \item \ref{devicenormative:Reserved Feature Bits}
 \end{itemize}
 
diff --git a/content.tex b/content.tex
index 0a62dce..b6b1859 100644
--- a/content.tex
+++ b/content.tex
@@ -502,6 +502,27 @@ \section{Exporting Objects}\label{sec:Basic Facilities of a Virtio Device / Expo
 types. It is RECOMMENDED that devices generate version 4
 UUIDs as specified by \hyperref[intro:rfc4122]{[RFC4122]}.
 
+\section{Preserve Resources}\label{sec:Basic Facilities of a Virtio Device / Preserve Resources}
+
+As virtio devices are paravirtualization devices by design.
+There are various devices resources created by sending commands
+from frontend and stored in backend.
+
+In some scenes, resources may be destroyed or reset, some of
+them can be re-created since frontend has enough information
+, but some can't. At this case, we can set \field{Preserve Resources}
+to 1 by specific transport, to prevent resources being destroyed.
+
+Which kind of resources need to be preserved and how to preserve
+resources depend on specific devices.
+
+\drivernormative{\subsection}{Preserve Resources}{Basic Facilities of a Virtio Device / Preserve resources}
+A driver SHOULD set \field{Preserve Resources} to 1 when there is a need
+to preserve resources.
+
+\devicenormative{\subsection}{Preserve Resources}{Basic Facilities of a Virtio Device / Preserve resources}
+A device MUST NOT destroy resources until \field{Preserve Resources} is 0.
+
 \input{admin.tex}
 
 \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
@@ -872,6 +893,10 @@ \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_PRESERVE_RESOURCES(42)] This feature indicates
+  that the device need to preserve resources.
+  See \ref{sec:Basic Facilities of a Virtio Device / Preserve Resources}.
+
 \end{description}
 
 \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
diff --git a/transport-pci.tex b/transport-pci.tex
index a5c6719..f6eea65 100644
--- a/transport-pci.tex
+++ b/transport-pci.tex
@@ -325,6 +325,7 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
         /* About the administration virtqueue. */
         le16 admin_queue_index;         /* read-only for driver */
         le16 admin_queue_num;         /* read-only for driver */
+        le16 preserve_resources;        /* read-write */
 };
 \end{lstlisting}
 
@@ -428,6 +429,11 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
 	The value 0 indicates no supported administration virtqueues.
 	This field is valid only if VIRTIO_F_ADMIN_VQ has been
 	negotiated.
+
+\item[\field{preserve_resources}]
+        The driver writes this to let device preserve resources whenever driver has demands.
+        1 - device need to preserve resources which can't be re-created, until 0 is set.
+        0 - all resources can be destroyed.
 \end{description}
 
 \devicenormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}
-- 
2.34.1


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