On Mon, Oct 27, 2025 at 11:42 AM Alex Bennée alex.bennee@linaro.org wrote:
"Edgar E. Iglesias" edgar.iglesias@amd.com writes:
Hi all,
This the RFC I'm preparing to send to upstream QEMU for initial RFC
review.
I didn't see much precedence for Signed-off-by lines in cover letter so
instead
I'm thinking to explicitely CC Bill and Alex and anyone else who would
like to be
on copy, just let me know.
Changes from v1:
- Move VIRTIO_MSG_VENDOR_ID to virtio-msg.c
- Update to match recent spec changes (token + set/get_vqueue padding)
- Add endian conversion of dev_num and msg_size
- Add instructions for running on GPEX PCI x86 microVM and ARM virt
- Add missing spsc_queue.h
This adds virtio-msg, a new virtio transport. Virtio-msg works by exchanging messages over a bus and doesn't rely on trapping and emulating making it a good fit for a number of applications such as AMP, real-time and safety applications.
Together with the new transport, this series adds a PCI device that implements an AMP setup much like it would look if two SoC's would use virtio-msg across a PCI link.
Current limitations: We only support a single device per bus (dev_num = 0). Shared memory queue layout likely to change in the future. Temporarily uses PCI Vendor Xilinx / Device 0x9039. Missing documentation.
Why can't the module be built-in?
It was due to a bug in the kernel driver, I fixed it last week.
There's been a ton of updates during the weekend, I've pushed them to the repos:
QEMU with these patches: https://github.com/edgarigl/qemu/tree/edgar/virtio-msg-rfc
Linux with virtio-msg suppport: https://github.com/edgarigl/linux/tree/edgari/virtio-msg-6.17
Changes: * Multi-device support (dev_num) * Actual echo of token * Tweak qom bus structure, avoids bug in 'info qtree' and needed for multi-device
With the latest commits, command-lines have changed slightly:
x86/q35: -device virtio-msg-amp-pci -device virtio-net-device,netdev=n1,bus=/q35-pcihost/pcie.0/virtio-msg-amp-pci/fifo0/virtio-msg/bus0/virtio-msg-dev -netdev user,id=n1
ARM virt: -device virtio-msg-amp-pci \ -device virtio-net-device,netdev=n1,bus=/gpex-pcihost/pcie.0/virtio-msg-amp-pci/fifo0/virtio-msg/bus0/virtio-msg-dev -netdev user,id=n1
We can now also add multiple devs, for example to add an additional virtio-net on dev_num = 1: -device virtio-net-device,netdev=n2,bus=/gpex-pcihost/pcie.0/virtio-msg-amp-pci/fifo0/virtio-msg/bus1/virtio-msg-dev -netdev user,id=n2
Cheers, Edgar
It hangs in this case:
ACPI: button: Power Button [PWRB] virtio_msg_amp_pci 0000:00:03.0: enabling device (0000 -> 0002) virtio_msg_amp_pci 0000:00:03.0: device_name=0000:00:03.0 virtio_msg_amp_pci 0000:00:03.0: mmr (BAR0) at 0x0000000010040000, size 0x0000000000004000 virtio_msg_amp_pci 0000:00:03.0: mmr (BAR1) at 0x0000000010044000, size 0x0000000000004000 ram=(____ptrval____) virtio_msg_amp_pci 0000:00:03.0: SHMEM @ 0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 virtio_msg_amp_pci 0000:00:03.0: get bus name for dev_id=0
tracing through we get to:
transport_msg_prepare (vmdev=0xffffff80c0a9c8c0, msg_id=2 '\002', payload_size=0) at /home/alex/lsrc/linux.git/drivers/virtio/virtio_msg.c:54 54 msg_prepare(vmdev->request, false, msg_id, vmdev->dev_id, payload_size); (gdb) n 106 transport_msg_prepare(vmdev, VIRTIO_MSG_DEVICE_INFO, 0); (gdb) ^C Thread 4 received signal SIGINT, Interrupt. [Switching to Thread 1.4] cpu_do_idle () at /home/alex/lsrc/linux.git/arch/arm64/kernel/idle.c:32 32 arm_cpuidle_restore_irq_context(&context); (gdb) bt #0 cpu_do_idle () at /home/alex/lsrc/linux.git/arch/arm64/kernel/idle.c:32 #1 0xffffffc0813a1a40 in arch_cpu_idle () at /home/alex/lsrc/linux.git/arch/arm64/kernel/idle.c:44 #2 0xffffffc0813a1ba8 in default_idle_call () at /home/alex/lsrc/linux.git/kernel/sched/idle.c:122 #3 0xffffffc08012baa8 in cpuidle_idle_call () at /home/alex/lsrc/linux.git/kernel/sched/idle.c:190 #4 do_idle () at /home/alex/lsrc/linux.git/kernel/sched/idle.c:330 #5 0xffffffc08012bd74 in cpu_startup_entry (state=state@entry=CPUHP_AP_ONLINE_IDLE) at /home/alex/lsrc/linux.git/kernel/sched/idle.c:428 #6 0xffffffc080048798 in secondary_start_kernel () at /home/alex/lsrc/linux.git/arch/arm64/kernel/smp.c:271 #7 0xffffffc080056078 in __secondary_switched () at /home/alex/lsrc/linux.git/arch/arm64/kernel/head.S:404 Backtrace stopped: previous frame identical to this frame (corrupt stack?)
but I can't see where the kernel would trigger a schedule....
The virtio-msg spec: https://github.com/Linaro/virtio-msg-spec/
QEMU with these patches: https://github.com/edgarigl/qemu/tree/edgar/virtio-msg-rfc
Linux with virtio-msg suppport: https://github.com/edgarigl/linux/tree/edgari/virtio-msg-6.17
To try it, first build Linux with the following enabled: CONFIG_VIRTIO_MSG=y CONFIG_VIRTIO_MSG_AMP=y CONFIG_VIRTIO_MSG_AMP_PCI=y
Boot linux in QEMU with a virtio-msg-amp-pci device, in this example with a virtio-net device attached to it:
x86/q35 machine: -device virtio-msg-amp-pci -device
virtio-net-device,netdev=n1,bus=/q35-pcihost/pcie.0/virtio-msg-amp-pci/vmsg.0
-netdev user,id=n1
x86/microvm or ARM virt machines: -device virtio-msg-amp-pci -device
virtio-net-device,netdev=n1,bus=/gpex-pcihost/pcie.0/virtio-msg-amp-pci/vmsg.0/virtio-msg/virtio-msg-proxy-bus.0
-netdev user,id=n1
Cheers, Edgar
Edgar E. Iglesias (4): virtio: Introduce notify_queue virtio: Add virtio_queue_get_rings virtio: Add the virtio-msg transport virtio-msg-bus: amp-pci: Add generic AMP PCI device
hw/misc/Kconfig | 7 + hw/misc/meson.build | 1 + hw/misc/virtio-msg-amp-pci.c | 324 ++++++++++++ hw/virtio/Kconfig | 4 + hw/virtio/meson.build | 5 + hw/virtio/virtio-msg-bus.c | 89 ++++ hw/virtio/virtio-msg.c | 598 ++++++++++++++++++++++ hw/virtio/virtio.c | 23 + include/hw/virtio/spsc_queue.h | 213 ++++++++ include/hw/virtio/virtio-bus.h | 1 + include/hw/virtio/virtio-msg-bus.h | 95 ++++ include/hw/virtio/virtio-msg-prot.h | 749 ++++++++++++++++++++++++++++ include/hw/virtio/virtio-msg.h | 45 ++ include/hw/virtio/virtio.h | 2 + 14 files changed, 2156 insertions(+) create mode 100644 hw/misc/virtio-msg-amp-pci.c create mode 100644 hw/virtio/virtio-msg-bus.c create mode 100644 hw/virtio/virtio-msg.c create mode 100644 include/hw/virtio/spsc_queue.h create mode 100644 include/hw/virtio/virtio-msg-bus.h create mode 100644 include/hw/virtio/virtio-msg-prot.h create mode 100644 include/hw/virtio/virtio-msg.h
-- Alex Bennée Virtualisation Tech Lead @ Linaro