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Subject: [PATCH v4 1/1] Introduce MGMT Admin commands
Introduce the concept of a management and a managed device. A
management device supports the VIRTIO_ADMIN_DEVICE_MGMT,
VIRTIO_ADMIN_DEVICE_MGMT_CAPS, VIRTIO_ADMIN_DEVICE_MGMT_ATTRS and
VIRTIO_ADMIN_MANAGED_DEVICE_LIST commands to manage some resources of
the managed device.
Also introduce a new mechanism to issue commands with dst_type field
that is not "self". With the new mechanism, driver can set dst_type to 1
and use the the vdev_id common field to describe the target vdev_id.
This mechanism is useful for virtio subsystems with multiple devices
with various different capabilities. For example, a virtio subsystem
that contains a PCI PF and its VF. For this subsystem, a clever system
administrator can use admin commands to map between a vdev_id and a VF
number and use it to manipulate the VF resources.
As we know, a typical cloud provider SR-IOV use case is to create many
VFs for use by guest VMs. The VFs may not be assigned to a VM until a
user requests a VM of a certain size, e.g., number of CPUs. A VF may
need MSI-X vectors proportional to the number of CPUs in the VM, but
there is no standard way today in the spec to change the number of MSI-X
vectors supported by a VF, although there are some operating systems
that support this.
The new admin mechanism manages the MSI-X interrupt vectors assignments
of a managed PCI device (i.e. VF) by its management devices (i.e. its
parent PF) but can easily extended to any other generic resource
management.
Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
---
admin.tex | 205 +++++++++++++++++++++++++++++++++++++++++++++--
content.tex | 88 ++++++++++++++++++++
introduction.tex | 25 ++++++
3 files changed, 310 insertions(+), 8 deletions(-)
diff --git a/admin.tex b/admin.tex
index ed9f6bd..f069dd5 100644
--- a/admin.tex
+++ b/admin.tex
@@ -9,11 +9,13 @@ \section{Admin command set}\label{sec:Basic Facilities of a Virtio Device / Admi
le16 command;
/*
* 0 - self
- * 1 - 65535 are reserved
+ * 1 - other virtio device in the same subsystem (described by vdev_id)
+ * 2 - 65535 are reserved
*/
le16 dst_type;
+ le64 vdev_id;
/* reserved for common cmd fields */
- u8 reserved[20];
+ u8 reserved[12];
u8 command_specific_data[];
/* Device-writable part */
@@ -37,9 +39,12 @@ \section{Admin command set}\label{sec:Basic Facilities of a Virtio Device / Admi
\hline
03h & VIRTIO_ADMIN_STATUS_INVALID_FIELD & invalid field was set \\
\hline
+04h & VIRTIO_ADMIN_STATUS_INVALID_VDEV_ID & invalid vdev_id was set \\
+\hline
+
\end{tabular}
-The \field{command}, \field{dst_type} and \field{command_specific_data} are
+The \field{command}, \field{dst_type}, \field{vdev_id} and \field{command_specific_data} are
set by the driver, and the device sets the \field{status}, the
\field{command_specific_error} and the \field{command_specific_result},
if needed.
@@ -48,9 +53,12 @@ \section{Admin command set}\label{sec:Basic Facilities of a Virtio Device / Admi
The mandatory fields to be set by the driver, for all admin commands, are \field{command} and \field{dst_type}.
+The optional unused fields to be zeroed by the driver.
+
The \field{command} defines the opcode for the command. The value for each command can be found in each command section.
-The \field{dst_type} defines the target virtio device for the command. This value should be set to 0 (self).
+The \field{dst_type} defines the target virtio device for the command. This value can be set to 0 (self) or 1 (other virtio device in the same subsystem).
+If \field{dst_type} is set to 1, the \field{vdev_id} is valid and used to describe the vdev_id of the target virtio device.
The \field{command_specific_error} should be inspected by the driver only if \field{status} is set to
VIRTIO_ADMIN_STATUS_CS_ERR by the device. In this case, the content of \field{command_specific_error}
@@ -69,12 +77,25 @@ \section{Admin command set}\label{sec:Basic Facilities of a Virtio Device / Admi
\hline
0002h & VIRTIO_ADMIN_DEVICE_INFO & O \\
\hline
-0003h - 7FFFh & Generic admin cmds & - \\
+0003h & VIRTIO_ADMIN_DEVICE_MGMT & O \\
+\hline
+0004h & VIRTIO_ADMIN_DEVICE_MGMT_CAPS & O \\
+\hline
+0005h & VIRTIO_ADMIN_DEVICE_MGMT_ATTRS & O \\
+\hline
+0006h & VIRTIO_ADMIN_MANAGED_DEVICE_LIST & O \\
+\hline
+0007h - 7FFFh & Generic admin cmds & - \\
\hline
8000h - FFFFh & Reserved & - \\
\hline
\end{tabular}
+\begin{note}
+{The following commands are mandatory for management devices: VIRTIO_ADMIN_DEVICE_IDENTIFY, VIRTIO_ADMIN_DEVICE_INFO,
+VIRTIO_ADMIN_DEVICE_MGMT, VIRTIO_ADMIN_DEVICE_MGMT_CAPS, VIRTIO_ADMIN_DEVICE_MGMT_ATTRS and VIRTIO_ADMIN_MANAGED_DEVICE_LIST.}
+\end{note}
+
\subsection{VIRTIO ADMIN DEVICE IDENTIFY command}\label{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE IDENTIFY command}
The VIRTIO_ADMIN_DEVICE_IDENTIFY command has no command specific data set by the driver.
@@ -89,7 +110,9 @@ \subsection{VIRTIO ADMIN DEVICE IDENTIFY command}\label{sec:Basic Facilities of
* (1 means that field was returned):
* Bit 0 - vdev_id
* Bit 1 - optional_caps_support
- * Bits 2 - 63 - reserved for future fields
+ * Bit 2 - num_supported_managed_vdevs
+ * Bit 3 - max_managed_vdev_id
+ * Bits 4 - 63 - reserved for future fields
*/
le64 attrs_mask;
le64 vdev_id;
@@ -97,10 +120,16 @@ \subsection{VIRTIO ADMIN DEVICE IDENTIFY command}\label{sec:Basic Facilities of
* capabilities are supported by the device:
* Bit 0 - if set, VIRTIO_ADMIN_SUBSYSTEM_IDENTIFY supported
* Bit 1 - if set, VIRTIO_ADMIN_DEVICE_INFO supported
- * Bits 2 - 63 - reserved for future capabilities.
+ * Bit 2 - if set, the device is a direct management device
+ * Bits 3 - 63 - reserved for future capabilities.
*/
le64 optional_caps_support;
- u8 reserved[4072];
+ /* Number of supported managed virtio devices by the target virtio device */
+ le64 num_supported_managed_vdevs;
+ /* Maximum value of a valid managed vdev_id for the target virtio device */
+ le64 max_managed_vdev_id;
+
+ u8 reserved[4056];
};
\end{lstlisting}
@@ -158,6 +187,166 @@ \subsection{VIRTIO ADMIN DEVICE INFO command}\label{sec:Basic Facilities of a Vi
specification and can't be equal to zero. If bit 0 is not set, the driver will ignore \field{vf_number}.}
\end{note}
+\subsection{VIRTIO ADMIN DEVICE MGMT command}\label{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT command}
+
+The VIRTIO_ADMIN_DEVICE_MGMT command is used by a management device to manage resources of other virtio devices within
+the virtio subsystem.
+The \field{command} is set to VIRTIO_ADMIN_DEVICE_MGMT.
+
+The command specific data set by the driver is of form:
+\begin{lstlisting}
+struct virtio_admin_device_mgmt_data {
+ /*
+ * 0 - reserved
+ * 1 - assign resource to the subject vdev_id
+ * 2 - query resource of the subject vdev_id
+ * 3 - 255 are reserved
+ */
+ u8 operation;
+ /*
+ * 0 - MSI-X vector
+ * 1 - 65535 are reserved
+ */
+ le16 resource;
+ /* The amount of elements for the operation to the given resource */
+ le32 resource_count;
+ u8 reserved[57];
+};
+\end{lstlisting}
+
+The following table describes the command specific error codes codes:
+
+\begin{tabular}{|l|l|l|}
+\hline
+Opcode & Status & Description \\
+\hline \hline
+00h & VIRTIO_ADMIN_CS_ERR_VDEV_IN_USE & target device is in use, operation failed \\
+\hline
+01h & VIRTIO_ADMIN_CS_ERR_RSC_COUNT_EXCEED & resource count exceed the max possible value \\
+\hline
+02h & VIRTIO_ADMIN_CS_ERR_NO_RSC & Mgmt device don't have requested resource count \\
+\hline
+03h & VIRTIO_ADMIN_CS_RSC_UNSUPPORTED & unsupported or invalid resource \\
+\hline
+04h & VIRTIO_ADMIN_CS_OP_UNSUPPORTED & unsupported or invalid operation \\
+\hline
+05h - FFh & Reserved & - \\
+\hline
+\end{tabular}
+
+This command, upon success, returns a data buffer that describes the information according to the requested operation.
+This information is of form:
+\begin{lstlisting}
+struct virtio_admin_device_mgmt_result {
+ le32 resource_count;
+ u8 reserved[12];
+};
+\end{lstlisting}
+
+If the requested operation was "assign resource to the subject vdev_id", the resource_count will return the count of the assigned
+resources to the subject vdev_id. Upon success, this value should be equal to the \field{resource_count} of the virtio_admin_device_mgmt_data
+structure. In case of a failure, the value of this field is undefined.
+
+If the requested operation was "query resource of the subject vdev_id", the resource_count will return the count of the currently assigned
+resources to the subject vdev_id upon success. In case of a failure, the value of this field is undefined.
+
+\begin{note}
+{MSI-X vector resource type is valid only for PCI devices. VIRTIO_ADMIN_CS_RSC_UNSUPPORTED error is
+returned when the destination device is not a PCI device.}
+\end{note}
+
+\begin{note}
+{For this command, if setting \field{resource} to MSI-X vector type, the \field{vdev_id} can't be associated to a Virtual Function with
+VF index greater than NumVFs value as defined in the PCI specification or smaller than 1. An error is returned when \field{vdev_id} is out of the range.}
+\end{note}
+
+\subsection{VIRTIO ADMIN DEVICE MGMT CAPS command}\label{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT CAPS command}
+
+The VIRTIO_ADMIN_DEVICE_MGMT_CAPS upon success, returns a data buffer that describes the management device capabilities.
+The \field{command} is set to VIRTIO_ADMIN_DEVICE_MGMT_CAPS.
+
+Upon success, the returned data buffer is of form:
+\begin{lstlisting}
+struct virtio_admin_device_mgmt_caps_result {
+ /*
+ * caps[0] - Bit 0, if set, MSI-X vector resource mgmt is supported
+ * Bit 1 - Bit 7 are reserved
+ * caps[1] - Bit 0 - Bit 7 are reserved
+ * caps[2] - Bit 0 - Bit 7 are reserved
+ * ....
+ * caps[8191] - Bit 0 - Bit 7 are reserved
+ */
+ u8 caps[8191];
+};
+\end{lstlisting}
+
+\begin{note}
+{MSI-X vector resource management is applicable only for PCI devices. Thus, MSI-X vector resource
+capability bit can be set to 1 only if the subject vdev_id is a management device that can manage PCI devices (e.g. PCI Physical Function virtio device).
+For more details on MSI-X vector management support see section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Admin command set / MSI-X vector management}.}
+\end{note}
+
+\subsection{VIRTIO ADMIN DEVICE MGMT ATTRS command}\label{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT ATTRS command}
+
+The VIRTIO_ADMIN_DEVICE_MGMT_ATTRS upon success, returns a data buffer that describes the management device attributes.
+The \field{command} is set to VIRTIO_ADMIN_DEVICE_MGMT_ATTRS.
+
+Upon success, the returned data buffer is of form:
+\begin{lstlisting}
+struct virtio_admin_device_mgmt_attrs_result {
+ /* For compatibility - indicates which of the below fields were returned
+ * (1 means that field was returned):
+ * Bit 0 - vfs_total_msix_count
+ * Bit 1 - vfs_assigned_msix_count
+ * Bit 2 - per_vf_max_msix_count
+ * Bits 3 - 63 - reserved for future fields
+ */
+ le64 attrs_mask;
+
+ /* Total number of msix vectors for the total number of VFs */
+ le32 vfs_total_msix_count;
+ /* Assigned number of msix vectors for the enabled VFs */
+ le32 vfs_assigned_msix_count;
+ /* Max number of msix vectors that can be assigned for a single VF */
+ le16 per_vf_max_msix_count;
+
+ u8 reserved[4078];
+};
+\end{lstlisting}
+
+\begin{note}
+{The \field{vfs_total_msix_count}, \field{vfs_assigned_msix_count} and \field{per_vf_max_msix_count} returned if the
+subject vdev_id is a management device that can allocate/deallocate MSI-X resources for PCI VFs devices.
+Otherwise, the associated bits in \field{attrs_mask} are zeroed.}
+\end{note}
+
+\subsection{VIRTIO ADMIN MANAGED DEVICE LIST command}\label{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN MANAGED DEVICE LIST command}
+
+The VIRTIO_ADMIN_MANAGED_DEVICE_LIST upon success, returns a data buffer that describes an ordered list of up to 510 managed
+virtio devices, in ascending order, that can be managed by the target management virtio device.
+The returned list contain device identifiers with vdev_id greater than or equal to the value of \field{first_vdev_id} in the command specific data.
+The \field{command} is set to VIRTIO_ADMIN_MANAGED_DEVICE_LIST.
+
+The command specific data set by the driver is of form:
+\begin{lstlisting}
+struct virtio_admin_managed_device_list_data {
+ le64 first_vdev_id;
+};
+\end{lstlisting}
+
+Upon success, the returned data buffer is of form:
+\begin{lstlisting}
+struct virtio_admin_managed_device_list_result {
+ /* Number of entries in the vdev_ids list */
+ le16 num_identifiers;
+ /* Number of currently valid managed virtio devices by the target virtio device */
+ le64 num_managed_vdevs;
+ u8 reserved[6];
+ /* List of managed vdev_ids. Only first num_identifiers are valid. */
+ le64 vdev_ids[510];
+};
+\end{lstlisting}
+
\section{Admin Virtqueues}\label{sec:Basic Facilities of a Virtio Device / Admin Virtqueues}
An admin virtqueue is a management interface of a device that can be used to send administrative
diff --git a/content.tex b/content.tex
index bf46192..27353ba 100644
--- a/content.tex
+++ b/content.tex
@@ -451,6 +451,19 @@ \section{Exporting Objects}\label{sec:Basic Facilities of a Virtio Device / Expo
\input{admin.tex}
+\section{Device management}\label{sec:Basic Facilities of a Virtio Device / Device management}
+
+A virtio subsystem might be consist of one or more virtio devices. For example, virtio PCI PF and its VFS compose a virtio subsystem.
+A capable PCI PF device might act as the management device in the subsystem, and its PCI VFs are the managed devices.
+A management device might have various management capabilities and attributes to manage its managed devices. The capabilities exposed
+in the result of VIRTIO_ADMIN_DEVICE_MGMT_CAPS command (see section \ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT CAPS command}
+for more details) and the attributes in the result of VIRTIO_ADMIN_DEVICE_MGMT_ATTRS command (see section \ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT ATTRS command}
+for more details). The list of the managed devices returned in the result of VIRTIO_ADMIN_MANAGED_DEVICE_LIST command
+(see section \ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN MANAGED DEVICE LIST command})
+
+The management device will use the VIRTIO_ADMIN_DEVICE_MGMT admin command to manage its managed devices (see section
+\ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT command} for more details).
+
\chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
We start with an overview of device initialization, then expand on the
@@ -1759,6 +1772,81 @@ \subsubsection{Driver Handling Interrupts}\label{sec:Virtio Transport Options /
\end{itemize}
\end{itemize}
+\subsection{PCI-specific Admin capabilities}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Admin capabilities}
+
+This documents the group of Admin capabilities for PCI virtio devices. Each capability is
+implemented using one or more Admin queue commands.
+
+\subsubsection{MSI-X vector management}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Admin command set / MSI-X vector management}
+
+This capability enables a virtio management device to control the assignment of MSI-X interrupt vectors
+for its managed devices. In PCI, a management device can be the PF device and the managed device can be the VF.
+Capable management devices will need to implement VIRTIO_ADMIN_DEVICE_MGMT, VIRTIO_ADMIN_DEVICE_MGMT_CAPS, VIRTIO_ADMIN_DEVICE_MGMT_ATTRS
+and VIRTIO_ADMIN_MANAGED_DEVICE_LIST admin commands, report the MSI-X attributes in the result of VIRTIO_ADMIN_DEVICE_MGMT_ATTRS and report that MSI-X
+vector resource management is supported by setting bit 1 of caps[0] in the result of VIRTIO_ADMIN_DEVICE_MGMT_CAPS admin command.
+See sections \ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT CAPS command} and
+\ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT ATTRS command} for more details.
+
+In the result of VIRTIO_ADMIN_DEVICE_MGMT_ATTRS admin command, a capable management device will return the total number of
+msix vectors for its VFs in \field{vfs_total_msix_count} field, the number of already assigned msix vectors for its VFs in
+\field{vfs_assigned_msix_count} field and also the maximal number of msix vectors that can be assigned for a single VF in
+\field{per_vf_max_msix_count} field. In addition, bit 0, bit 1 and bit 2 are set to indicate on the validity of the other 3
+fields in the \field{attrs_mask} field of the result buffer.
+See section \ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT ATTRS command} for more details.
+
+In the result of VIRTIO_ADMIN_MANAGED_DEVICE_LIST admin command, a capable management device will return a list of associated managed virtio devices.
+See section \ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN MANAGED DEVICE LIST command} for more details.
+
+A management device that supports VFs MSI-X vector management capability, will allocate MSI-X resources provided by the parent PF of the SR-IOV VFs.
+The default assignment of the MSI-X vectors for managed devices is out of the scope of this specification.
+A driver, using VIRTIO_ADMIN_DEVICE_MGMT can update the MSI-X assignment for a specific managed device.
+In the data of VIRTIO_ADMIN_DEVICE_MGMT admin command, a driver set the \field{resource} type to be MSI-X vector and the
+amount of MSI-X interrupt vectors to configure to the subject managed device in \field{resource_count}. The managed device id is set to \field{vdev_id} field.
+
+A successful operation guarantees that the requested amount of MSI-X interrupt vectors was assigned to the subject management device.
+This value is also returned in the virtio_admin_device_mgmt_result structure.
+Also, a successful operation guarantees that the MSI-X capability access by the subject PCI device defined by the PCI specification must reflect
+the new configuration in all relevant fields. For example, by default if the PCI VF has been assigned 4 MSI-X vectors, and VIRTIO_ADMIN_DEVICE_MGMT
+increases the MSI-X vectors to 8; on this change, reading Table size field of the MSI-X message control register will reflect a value of 7.
+
+It is beyond the scope of the virtio specification to define necessary synchronization in system software to ensure that a virtio PCI VF device
+interrupt configuration modification is reflected in the PCI device. However, it is expected that any modern system software implementing virtio
+drivers and PCI subsystem will ensure that any changes occurring in the VF interrupt configuration is either updated in the PCI VF device or
+such configuration fails.
+
+To query amount of MSI-X interrupt vectors that is currently assigned to a managed device, the driver issue VIRTIO_ADMIN_DEVICE_MGMT with \field{operation} set to
+"query resource of the subject vdev_id" value (== 2). The driver also set the \field{resource} type to be MSI-X vector and the managed device id is set to \field{vdev_id}
+field. In the result of a successful operation, the amount of MSI-X interrupt vectors that is currently assigned to the subject managed device is
+returned by the device in \field{resource_count} field of the virtio_admin_device_mgmt_result structure.
+See section \ref{sec:Basic Facilities of a Virtio Device / Admin command set / VIRTIO ADMIN DEVICE MGMT command} for more details.
+
+\paragraph{MSI-X configuration sequence example}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Admin command set / VF MSI-X control / MSI-X configuration sequence example }
+
+A typical sequence for configuring MSI-X vectors for PCI VFs using MSI-X vector management mechanism is following:
+
+\begin{enumerate}
+\item Ensure that driver doesn't run and it is safe to change MSI-X (e.g. disable sriov auto probing)
+
+\item Load the PF driver
+
+\item Enable SR-IOV by following the PCI specification
+
+\item Query the management device capabilities using commands VIRTIO_ADMIN_DEVICE_IDENTIFY, VIRTIO_ADMIN_DEVICE_MGMT_CAPS and VIRTIO_ADMIN_DEVICE_MGMT_ATTRS
+
+\item Find the managed VF vdev_id using commands VIRTIO_ADMIN_MANAGED_DEVICE_LIST and VIRTIO_ADMIN_DEVICE_INFO
+
+\item Query the VF MSI-X configuration using command VIRTIO_ADMIN_DEVICE_MGMT (query operation)
+
+\item Assign desired MSI-X configuration for the VF using command VIRTIO_ADMIN_DEVICE_MGMT (assign operation)
+
+\item After successful completion of the assignment, load the VF driver
+
+\item Assign the VF to a VM
+
+\item After VM/VF use is completed, user assigns different MSI-X value and repeats the steps of 7 onwards
+
+\end{enumerate}
+
\section{Virtio Over MMIO}\label{sec:Virtio Transport Options / Virtio Over MMIO}
Virtual environments without PCI support (a common situation in
diff --git a/introduction.tex b/introduction.tex
index 94dd7a2..b5906c8 100644
--- a/introduction.tex
+++ b/introduction.tex
@@ -260,5 +260,30 @@ \subsection{virtio subsystem}\label{sec:Introduction / Definitions / virtio subs
VQN and vdev_id are exposed via Admin Command Set.
+\subsection{virtio management device}\label{sec:Introduction / Definitions / virtio management device}
+
+A virtio device that supports VIRTIO_ADMIN_DEVICE_MGMT, VIRTIO_ADMIN_DEVICE_MGMT_CAPS, VIRTIO_ADMIN_DEVICE_MGMT_ATTRS and
+VIRTIO_ADMIN_MANAGED_DEVICE_LIST Admin commands and can manage a virtio managed device.
+A virtio subsystem may contain zero or more management devices.
+
+A PCI SR-IOV Physical Function based virtio device is an example of a possible virtio management device.
+
+\subsection{virtio direct management device}\label{sec:Introduction / Definitions / virtio direct management device}
+
+A virtio management device that can set \field{dst_type} to 0 (self) and to 1 (other virtio device in the same subsystem), and set \field{vdev_id} to an id that corresponds with
+one of its managed virtio devices for the following admin commands (if these fields are applicable): VIRTIO_ADMIN_DEVICE_IDENTIFY, VIRTIO_ADMIN_DEVICE_INFO
+and VIRTIO_ADMIN_DEVICE_MGMT.
+
+The managed device list can be queried using VIRTIO_ADMIN_MANAGED_DEVICE_LIST.
+
+A virtio subsystem may contain zero or more direct management devices.
+
+\subsection{virtio managed device}\label{sec:Introduction / Definitions / virtio managed device}
+
+A virtio device that can be managed by a virtio management device.
+A virtio subsystem may contain zero or more managed devices.
+
+A PCI SR-IOV Virtual Function based virtio device is an example of a possible virtio managed device.
+
\newpage
--
2.21.0
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