Read intro below, and/or the preparation work at the bottom of this page. Then look at actual Document Work and Release page.
To allow further success of hypervisor environments in automotive it is essential that all vendors are able to provide compelling guest runtime environments that make the usual automotive I/O devices available. The essential devices could be defined and agreed upon by the industry. If such a set of devices and device features is defined a document can be crafted that defines these devices and their features that in their combination create a virtual platform.
Hand-waving about some virtual architecture is not our goal. The specification shall enable efficient reuse and collaborative progress among companies in this industry.
A virtual platform specification should be built upon already published work, where VIRTIO is the most prominent standard we have found, but add to it if this is not enough. It seems that the automotive industry may needs to extend some areas. At minimum it should review and bolster support for the parts most needed in the automotive industry, clarify which parts are required vs optional, and this work result should (will) one way or another make sure that different automotive initiatives combine into common agreements.
The project group has discussed and found consensus on how that automotive virtual platform specification can achieve this:
For an automotive virtualized platform, VIRTIO is primarily a starting point although increasing in breadth over time. Participating companies in this Hypervisor Group are also involved in proposing new functionality in future VIRTIO specifications, to cover audio, multimedia, and hardware accelerators and other unique hardware devices often found in automotive environments.
Instead of developing additional domain or even vendor specific device frameworks and models a collaborative development could greatly reduce the individual development of project efforts and thus spur the adoption of hypervisor based environments in the automotive sector.
Additional efforts definitely need to be spent in the area of audio virtualization and the in virtualization of co-processors like DSPs, image processors and codec accelerators. Developing a standard model for the diverse buses found in cars like CAN or ethernet AVB could also be additional fields of investigation.
In the work done here (see table below) we categorize device types and ensure that each need has been thoroughly analyzed so that as an industry we can truly define the right specification, to be applicable in >95% of the typical situations.
The VIRTIO standard aims to provide a standardized interface and device models for device para-virtualization in hypervisor environments.
With development going back until 20XX the virtio device model was first introduced for the educational "lguest" hypervisor and became the default I/O virtulaization method used with qemu/KVM and recently the default model used by many cloud providers. The virtio devices have been partially standardized by the OASIS standardisation body in 2015 with the VIRTIO 1.0 specification which describes the transport layer and a limited set of device models.
The currently standardized device models are: network, block, console, entropy, memory ballooning and SCSI devices. Additionally to the formally standardized devices several additional devices exists as "implemented" devices such as GPU, input, 9pfs, vsock and crypto. Some of which are currently in the process of standardization.
Virtio relies on a dma-like memory model meaning that all allocations are handled by the "driver" part of the device and the "device" implementation can directly access the allocated buffers for reading or writing. This enables a resource saving and fast operating mode. Metadata is transported using so called virt-queues that resemble ring-buffers. Depending on the architecture used, different transport and device discovery modes are supported: PCI for x86, mmio for ARM and channel-IO for s390. These transports are geared toward the most efficient implementation per CPU architecture and allow for efficient implementations depending on the environment.
In recent years some hardware devices, like network controllers and NVMe based storage systems have evolved to be similar or compatible with the VIRTIO protocol, to allow hardware assisted I/O virtualization using para-virtualized device models.
VIRTIO's main benefit for the automotive industry lies in it's sheer existence and operating system support. The fact that standardized device models exists allows for multiple compatible implementations of both driver and server parts of the system. The ubiquity of VIRTIO in cloud and enterprise virtualization makes drivers readily available in all major operating systems which keeps driver maintenance effort to a minimum.
Due to the driver defined memory allocation model, vendors can choose to limit the resource usage and define safety properties to their own requirements without impeding the standardized model and stay interoperable with existing device implementations.
The DMA-like nature of the devices allows for high-performant implementations that the easily compete with hardware assisted I/O virtualization models while still providing relative ease of implementation.
Many vendors of automotive grade hypervisors have already adopted virtio based devices into their system offerings due to the above mentioned reasons and the benefit of building upon these open source technologies has greatly improved the availability of commodity devices like network and block storage.
Vendor neutral industry bodies like GENVI and AGL can act a forum between hypervisor vendors, users and the hardware manufactures in a form that allows open collaboration in development and maintaining a standard platform definition.
The regular events can be used as occasions for interoperability testing and standard steering. The participation in the OASIS-VIRTIO committee can be delegated to such organization to voice the automotive industries concerns and advice in the technical committee.
GENIVI has in the past maintained domain specific APIs and standards can easily act as a body that makes sure the standard is not only maintained but also advanced as new technologies evolve.
AGL can provide the necessary collaboration with the upstream kernel project and the Linux Foundation which in-turn opens up for collaboration with the key industry players in cloud and enterprise computing.
For each topic:
Consider topics not yet listed (e.g. unique automotive requirements)
Note also: Bottom of this page has a "brainstorm" list of criteria to consider.
Virtual Device Categories
This table is now somewhat outdated and not used to drive the work any longer.
The key challenge for defining a shared virtual platform definition is to first identify the various device driver types such a platform must provide, and to evaluate if existing work so far (e.g. VIRTIO) covers what the automotive industry needs:
Completeness / Applicability evaluation
|Comments and discussion||Spec complete||Include in draft 1|
Ticket to track completion
|Block Storage||Flash/Disk/persistent storage|
Included also automotive persistence requirements.
|ready for review||Yes|
Access to (shared) physical ethernet
and guest-to-guest communication
Think about writing info how to share a physical network in practice
(Create bridge between virtual device and physical)
vsock should be moved to separate section? Agreed.
WiFi seems to be not well covered. Shall we wait on including it?
except WiFi - leave comment that it is work in progress)
|Console||Text terminal input||Gunnar|| ready for review||Yes|
|crypto||Access to cryptographic services |
| With new features, it is enough.|
We also added some
ready for review
Discussion part needs cleanup
Draft spec – requirements written
Uncertainty (and lots of ongoing development) around 3D APIs - Vulkan progress, etc.
See GPU Summary page
and requirements in spec draft
Still a moving target (3D). This is reflected in specification
3D: Proposal: include a discussion but requirements are not in Draft.
Dmitry Morozov please finish according to this.
3D requirements that are not accepted upstream were dropped.
Check status of EDID introduction.
|Input||Traditionally keyboard/mouse/etc |
- for automotive = expanded?
Now part of VIRTIO 1.1
Mouse/touch events may need to remap coordinates in combined virtual systems but interface may still not be affected by this.
|vsock||Communication between guest (VM) |
and host (hypervisor)
|Covered in networking chapter - to be put in its own (sub)chapter.|
ready for review
9pfs and other
|9P = protocol to expose host (hypervisor) |
file systems to the guest. FS=filesystem.
Completeness: Protocol: , VIRTIO spec: (see comment)
Need in Embedded/Automotive: None? Can we find a use-case?
Applicability: For what it does, seems ok. But might not be really needed and therefore "not applicable". Is there something else/more needed?
A note on its documentation/definition not being very precise
ready for review
(cut down chapter, should be OK)
OK to have such a verbose chapter? Maybe some more work...
IOMMU coordinates of DMA devices'
See IOMMU Summary page
Limit guest devices' scope to access system memory during DMA
Enable scatter-gather accesses due to remapping (DMA buffers do not need to be physically-contiguous)
Nested virtualization. Any use-cases for automotive?
ARM is actively working on the specification, more features are coming.
Nested virtualization? The use of Linux Containers inside a VM was mentioned. That in itself is not really nested virtualization. Namespace-based containers, is just a kernel feature providing separation independent of a hypervisor. However, Kata Containers is an approach to tie Linux containers into a hypervisor layer, making them "fully" virtualized. A theoretical situation arises that involves the use of Kata Containers on a Linux system that itself already runs in a VM. That might constitute an example of nested virtualization, but it was decided that this is not a mainstream idea, possibly not supported or feasible, and in each case likely more trouble than it is worth. "Flattening" the virtualization approach so that all units still run on one hypervisor is a likely outcome. Further research into partitioning methods is likely but for now this falls outside of a mainstream automotive virtual platform definition. We highlighted that Linux containers in their normal namespace based implementation are already a very useful system partition tool and it can be trivially applied also if the Linux kernel runs in a VM.
Chapter has been written.
Xen working on more secure implementation (memory visibility problem, security of VIRTIO approach) - want to keep this open requirement wise to have flexibility.
Latest proposal to VIRTIO was close to go in but withdrawn to address final comments.
Need a group review of text (verbose) and consider the comments here on the left.
And also VIRTIO parts have not been merged to official spec version.
Requirements to be removed?
VIRTIO proposal is being discussed - still pending 2019-09-25
Some info on Linux/Xen code here:
Artem Mygaiev - can this comment be removed? Should it affect the spec?
|Information is quite complete. and good understanding written. Needs cleanup to become a proper chapter|
Requirement set is NOT ready (merged).
Leave comment and/or discussion and future outlook but not requirement.
Not covered by VIRTIO specifically.
Artem proposed that Systems Control Management Interface (SCMI) protocol as a flexible and an appropriate abstraction for sensors. It is also appropriate for controlling power-management and related things. The hardware access implementation is according to ARM offloaded to a "Systems Control Processor" but this is a virtual concept. It could be a dedicated core in some cases, perhaps in others not. EPAM/Xen tried out putting code in ARM-TF, to act as this SCP.
SCMI destined (?) to become a ARM-wide standard in a currently fragmented reality.
Upper protocol defined, but could imagine different lower transport. One mailbox-style transport is kind-of defined by ARM spec? Discussion if VIRTIO transport would be appropriate. A "SCMI device" type added to VIRTIO?
What about PINCTRL, and handling the many multiplexed pins in a modern SoC. Any remaining need for lower-level protocols for accessing/virtualizing hardware?
CPUs/SoCs have "internal" sensors too. Relating to temperature and power mgmt. Some internal control tweaks for power management (core frequency / voltage) are like tiny internal actuators. Virtual access to those? Same or different APIs?
Some OS have requirements that must be met by "platform" - eg. Android requires orientation sensor.
Good work done.
Split out GPIO to separate chapter.
Placeholder also for describing HW passthrough (in general)
All 3 need another review and cleanup to be complete.
Consider platform requirement for sensors that must exist (for Android etc.)
|No requirements possible in draft spec.|
Possibly some of discussion and future outlook...
|Media Acceleration (VPUP, IPU, CODEC)||Hardware support for codec/processing|
Proposal to VIRTIO might come (OpenSynergy)
Gunnar AnderssonPlease check status - in VIRTIO mailing list...
|Not ready in time. Placeholder referencing currrent proposals.|
coprocessors and other
|Abstraction of SoC specifics|
|Not really in VIRTIO scope|
Matti: virtualize functions, not devices.
Gunnar: Analysis might extract some functions out of these...
|(not sure yet if we expect to cover it)|
Example Assigning Host USB device to a Guest VM in KVM, here:
Which use cases do we want to address?
•USB 2.0 (EHCI controller)
•On-The-Go (system can function as both USB host and USB device)
Needs update – see minutes.
|placeholder for future|
Other Serial devices?
... and LIN bus
VIRTIO applicability needs analysis
Spec chapter needs to be written.
UARTs are normally passed through (VM has access to memory mapped hardware) or forwarded (hardware access is done by HV and some abstract interface provided to the VMs) = virtio-console standard.
PL011 = ARM fast model UART controller, reference implementation in versatile-express. Provided in RPi and some other hw and virtual platforms.
Fold discussion into console chapter.
Uncertain what parts are specified and implemented (in VIRTIO and Linux)
Cover this in console chapter
emergency-write / early debugging could be left out if we are not done with it.
|CAN||virtio-can: VIRTIO-based CAN driver||Decide opinion and write chapter|
Possible, no firm standard. No specification - just an example driver implementation.
Anup Patel - can we summarize again?
|Time Sensitive Networks|
Need new volunteer to complete it, perhaps from GHS?
The required features are not present in the network virtio devices as of virtio 1.0.
Is this → applicable enough to move into specification as requirements? -->
Must have requirements:
Good to have:
General architectural considerations:
Comment on the possibility of implementing TSN is not prevented, (even without a virtual interface standard)
Need some more confirmation
OpenSynergy with BT experience ?
Not in VIRTIO scope
Virtualization of BT hardware might not be required. However, commenting on various system designs seems appropriate.
Example: There exists an interface for virtualized audio device (virtio-sound), but Bluetooth is also an audio device (among other things...) What does this mean for how to build an architecture that (for example) uses both virtualization for audio, and bluetooth technologies.
Write at least a Discussions chapter.
Not ready in time for first draft.
Must be mentioned, at least a comment and future plan.
|Memory Balloon Device||Gunnar||In VIRTIO. Applicability to automative is questionable.|
May be partly applicable - I could write something here to get us started. - Gunnar
RAM device is being discussed as a better solution later on.
|TODO||Not strictly necessary in the first draft version|
Random Number Generator
|Covered in the Crypto chapter.|
Very important for embedded systems... Let's see what is there and what we need to do.
SBSA has a generic interface, it should be the closest one.
Aim for simple interface.
Avoid VIRTIO/virt-queue type solution...
Want to include
The VIRTIO 1.0 specification is organized a bit differently, and more generic than our detailed list above. Here is a much abbreviated table of contents for VIRTIO 1.0, just to give an overview on the most important parts. Consider, especially, the limited types of devices. All defined devices are under these categories only for the 1.0 version.
2 Basic Facilities of a Virtio Device
3.1 Device Initialization
3.2 Device Operation
3.3 Device Cleanup
4 Virtio Transport Options
4.1 Virtio Over PCI Bus
4.2 Virtio Over MMIO
4.3 Virtio Over Channel I/O
5 Device Types
5.1 Network Device
5.2 Block Device
5.3 Console Device
5.4 Entropy Device
5.5 Traditional Memory Balloon Device
5.6 SCSI Host Device
7.2 Driver Conformance
7.3 Device Conformance
7.4 Legacy Interface: Transitional Device and Transitional Driver Conformance
B Creating New Device Types
When looking at a particular proposed device standard, evaluate characteristics/criteria:
- Is there a proposal for standard (specification)?
- Is it accepted in VIRTIO?
- Is it a de-facto standard?
- Implementation status
- ...In QEMU/Linux kernel?
- ...FOSS in a GitHub Repo?
- ...Commercial/closed-source implementations?
- ... Number of implementations?
- Complexity estimation?
- ... e.g. CAN Device class, vs GPU (need to consider large User-space
library, complex HALs,
- ...mostly implementation dependent? Are the technical requirements hindering implementing it efficiently, for some reason? Does it matter?
- Code Maturity?
-- ...implementation dependent, but evaluate that which exists
- Evaluate: Security aspects
- Evaluate: Functional Safety aspects
Importance for automotive use-case
- ...Is it generally applicable for many use cases or for a special case?