Re: [PATCH v1 0/4] virtio-msg transport layer

Arnaud POULIQUEN
2026-02-04T13:51:07Z

Hello,

On 2/3/26 14:21, Michael S. Tsirkin wrote:
> On Mon, Jan 26, 2026 at 11:32:26AM -0500, Bill Mills wrote:
>> This series adds the virtio-msg transport layer.
>>
>> The individuals and organizations involved in this effort have had difficulty in
>> using the existing virtio-transports in various situations and desire to add one
>> more transport that performs its transport layer operations by sending and
>> receiving messages.
>
> Is it arm and linaro, or more?
> If more, could we get some acks on list from the people involved?

STMicroelectronics is also interested in this transport.

I have already my signed off on patch 2/4. For the rest of the series:

Acked-by: Arnaud Pouliquen arnaud.pouliquen@foss.st.com

Thanks,
Arnaud

>
>
>> Implementations of virtio-msg will normally be done in multiple layers:
>> * common / device level
>> * bus level
>>
>> The common / device level defines the messages exchanged between the driver
>> and a device. This common part should lead to a common driver holding most
>> of the virtio specifics and can be shared by all virtio-msg bus implementations.
>> The kernel implementation in [3] shows this separation. As with other transport
>> layers, virtio-msg should not require modifications to existing virtio device
>> implementations (virtio-net, virtio-blk etc). The common / device level is the
>> main focus of this version of the patch series.
>>
>> The virtio-msg bus level implements the normal things a bus defines
>> (enumeration, dma operations, etc) but also implements the message send and
>> receive operations. A number of bus implementations are envisioned,
>> some of which will be reusable and general purpose. Other bus implementations
>> might be unique to a given situation, for example only used by a PCIe card
>> and its driver.
>>
>> The standard bus messages are an effort to avoid different bus implementations
>> doing the same thing in different ways for no good reason. However the
>> different environments will require different things. Instead of trying to
>> anticipate all needs and provide something very abstract, we think
>> implementation specific messages will be needed at the bus level. Over time,
>> if we see similar messages across multiple bus implementations, we will move to
>> standardize a bus level message for that.
>>
>> We are working on a few reusable bus implementations:
>>
>> * virtio-msg-ffa based on Arm FF-A interface for use between:
>> * normal world and secure world
>> * host and VM or VM to VM
>> * Can be used w/ or with out a hypervisor
>> * Any Hypervisor that implements FF-A can be used
>> * We have this working with pKVM and Xen
>> * We have this working with Trusty and OP-TEE
>>
>> * virtio-msg-amp for use between heterogenous systems
>> * The main processors and its co-processors on an AMP SOC
>> * Two or more systems connected via PCIe
>> * Minimal requirements: bi-directional interrupts and
>> at least one shared memory area
>> * hvac-demo has 2 demos of this
>> * This is working on two hardware platforms
>>
>> * virtio-msg-loopback for userspace implemented devices
>> * Allows user space to provide devices to its own kernel
>> * This is similar to fuse, cuse or loopback block devices but for virtio
>> * hvac-demo has a demo
>>
>> We also anticipate a few more:
>>
>> * virtio-msg-xen specific to Xen
>> * Usable on any Xen system (including x86 where FF-A does not exist)
>> * Using Xen events and page grants
>>
>> * virtio-msg over admin virtqueues
>> * This allows any virtio-pci device that supports admin virtqueues to also
>> support a virtio-msg bus that supports sub devices
>> * [We are looking for collaborators for this work]
>>
>> Changes since RFC2:
>>
>> Spec Functional:
>> * Made the common message header 8 bytes and added a token for optional use
>> when parallel outstanding requests are possible
>> * Made the 8 byte fields align to 8 byte offsets.
>> This effects the {SET,GET}_VQUEUE messages
>> * Many conformance cases have been tightened.
>>
>> Spec Editorial:
>> * Major restructure to better align with virtio spec
>> * Conformance model now matches other transports
>> * Use C structures to define messages instead of tables
>> * Added a section to describe how responses are matched to requests
>> This includes the use of the new token field
>> * Redefined / better described error handling between transport and bus
>> layers to eliminate the need for the bus to generate fake response messages
>> * Included editorial feedback from RFC2
>>
>> Eco-system:
>> * Added virtio-msg-loopback demo
>> * Arm has published the first draft of the virtio-msg over FFA spec [6]
>> * virtio-msg over FFA has been demonstrated with both Trusty and OP-TEE
>> secure world
>> * LKML RFC has been sent [7]
>> * QEMU RFC has been sent [8]
>>
>> This is the first non-RFC patch series. The known short comings have been
>> addressed. We ask for review in earnest on this series and thank you for
>> any feedback you can provide.
>>
>> Background info and work in progress implementations:
>> * HVAC project page with intro slides [1]
>> * HVAC demo repo w/ instructions in README.md [2]
>> * Kernel w/ virtio-msg common level and ffa support [3]
>> * QEMU w/ support for one form of virtio-msg-amp [4]
>> * Portable RTOS library w/ one form of virtio-msg-amp [5]
>>
>> In addition to the QEMU system based demos in the hvac-demo repo, we also have
>> two hardware systems running:
>> * AMD x86 + AMD Arm Versal connected via PCIe
>> * ST STM32MP157 A7 Linux using virtio-i2c provided by M4 Zephyr
>>
>> Please note that although the demos work, a few have not been aligned
>> with this version of the spec.
>>
>> [1] https://linaro.atlassian.net/wiki/spaces/HVAC/overview
>> [2] https://github.com/wmamills/hvac-demo
>> [3] https://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git/log/?h=virtio/msg
>> [4] https://github.com/edgarigl/qemu/commits/edgar/virtio-msg-rfc/
>> [5] https://github.com/arnopo/open-amp/commits/virtio-msg/
>> [6] https://documentation-service.arm.com/static/68f647791134f773ab3f0a7c
>> [7] https://lore.kernel.org/all/cover.1753865268.git.viresh.kumar@linaro.org/
>> [8] https://mail.gnu.org/archive/html/qemu-devel/2025-10/msg07438.html
>>
>> Bertrand Marquis (2):
>> virtio-msg: add new command for bus normative
>> virtio-msg: add conformance entries in conformance chapter
>>
>> Bill Mills (2):
>> virtio-msg: Add virtio-msg, a message based virtio transport layer
>> virtio-msg: link virtio-msg content
>>
>> commands.tex | 3 +-
>> conformance.tex | 105 ++-
>> content.tex | 1 +
>> transport-msg.tex | 1640 +++++++++++++++++++++++++++++++++++++++++++++
>> 4 files changed, 1746 insertions(+), 3 deletions(-)
>> create mode 100644 transport-msg.tex
>>
>> --
>> 2.34.1
>>
>