[RFC PATCH 0/6] virtio: Add support for Virtio message transport

[Viresh Kumar <viresh.kumar@linaro.org>]

Hello,

This RFC series introduces support for a new Virtio transport type:
"virtio-msg", as proposed in [1]. Unlike existing transport types like
virtio-mmio or virtio-pci, which rely on memory-mapped registers, virtio-msg
implements transport operations via structured messages. Those messages can be
transported through different mechanisms such as mailboxes, shared memory based
FIFO or specific protocols such as FF-A on Arm.

This series includes:
- Core virtio-msg transport support.
- Two message transport bus implementations:
  - virtio-msg-ffa: based on ARM's Firmware Framework for Arm (FF-A).
  - virtio-msg-loopback: a loopback device for testing and validation.

The code is available here for reference: [2] and virtio-msg loopback and FF-A
test setups are explained here: [3] and [4].

This series is based on v6.16 and depends on commit [5].


### Memory Mapping and Reserved Memory Usage

The first two patches enhance the reserved-memory subsystem to support attaching
struct device`s that do not originate from DT nodes — essential for virtual or
dynamically discovered devices like the FF-A or loopback buses.

This reserved-memory region enables:
- Restricting all DMA-coherent and streaming DMA memory to a controlled range.
- Allowing the remote endpoint to pre-map this memory, reducing runtime overhead.
- Preventing unintentional data leaks, since memory is typically shared at page
  granularity.
- For the loopback bus, it restricts the portion of kernel memory that can be
  mapped into userspace, improving safety.

Device association with reserved-memory regions is based on DT node naming
conventions, such as vmsglb@ or vmsgffa@, similar to the remoteproc framework’s
approach.

Feedback on the design, API, and approach is welcome.

--
Viresh

[1] https://lore.kernel.org/all/20250620224426.3923880-2-bill.mills@linaro.org/
[2] git://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git virtio/msg-rfc-v1
[3] https://linaro.atlassian.net/wiki/spaces/HVAC/pages/30104092673
[4] https://linaro.atlassian.net/wiki/spaces/HVAC/pages/29657792513
[5] From linux-next: 5be53630b4f0 virtio-mmio: Remove virtqueue list from mmio device


Viresh Kumar (6):
  of: reserved-memory: Add reserved_mem_device_init()
  of: reserved-memory: Add of_reserved_mem_lookup_by_name
  virtio: Add support for virtio-msg transport
  virtio-msg: Add optional userspace interface for message I/O
  virtio-msg: Add support for FF-A (Firmware Framework for Arm) bus
  virtio-msg: Add support for loopback bus

 MAINTAINERS                          |   7 +
 drivers/of/of_reserved_mem.c         |  91 +++-
 drivers/virtio/Kconfig               |  34 ++
 drivers/virtio/Makefile              |   5 +
 drivers/virtio/virtio_msg.c          | 655 +++++++++++++++++++++++++++
 drivers/virtio/virtio_msg_ffa.c      | 505 +++++++++++++++++++++
 drivers/virtio/virtio_msg_internal.h |  88 ++++
 drivers/virtio/virtio_msg_loopback.c | 323 +++++++++++++
 drivers/virtio/virtio_msg_user.c     | 140 ++++++
 include/linux/of_reserved_mem.h      |  13 +
 include/uapi/linux/virtio_msg.h      | 213 +++++++++
 include/uapi/linux/virtio_msg_ffa.h  |  94 ++++
 include/uapi/linux/virtio_msg_lb.h   |  22 +
 13 files changed, 2166 insertions(+), 24 deletions(-)
 create mode 100644 drivers/virtio/virtio_msg.c
 create mode 100644 drivers/virtio/virtio_msg_ffa.c
 create mode 100644 drivers/virtio/virtio_msg_internal.h
 create mode 100644 drivers/virtio/virtio_msg_loopback.c
 create mode 100644 drivers/virtio/virtio_msg_user.c
 create mode 100644 include/uapi/linux/virtio_msg.h
 create mode 100644 include/uapi/linux/virtio_msg_ffa.h
 create mode 100644 include/uapi/linux/virtio_msg_lb.h

-- 
2.31.1.272.g89b43f80a514