On Thu, Feb 19, 2026 at 02:03:27PM +0100, Albert Esteve wrote:
Hi all,
Thanks, I fully reviewed this and LGTM! I left some minor comments.
@Michael IIUC this is not applying on master, so I suggested to rebase
and send a new verions. Would be great if we can merge this before rc0.
Thanks,
Stefano
v12-v13
- SMEM_UNMAP spec update to explicitly state the use of
VHOST_USER_PROTOCOL_F_REPLY_ACK for replies
- Removed confusing remark for 0-sized regions in
GET_SHMEM_CONFIG
v11->v12
- Refined VIRTIO Shared Memory Region configuration mem size
spec description
- Removed unused name in vhost-user-base's vub_device_realize to
avoid build error
- Initialize shmem in vhost_user_backend_handle_shmem_unmap
to avoid compiler being confused
- Added stub for memory_region_init_ram_from_fd in memory.h
for windows builds
- Use memory_region_size for shmem_region handlers instead
of accessing size member directly in shmem mrs
v10->v11
- Rebase to grab commit fde5930cc37175cfcd0f03a089e26f4458a52311
and explicitly unset reply_ack on the SHMEM_MAP/UNMAP msg.
- Mention mapping cleanup on device reset in the spec.
v9->v10
- Fix transaction_commit invoked without transaction_begin
on vhost_user_backend_handle_shmem_map() early errors
- Removed fd tracking on VirtioSharedMemoryMapping, it
is handled by the RAMBlock
- Reject invalid BAR configurations when VIRTIO Shared Memory
Regions are in use by vhost-user-test-device
This patch series implements dynamic fd-backed memory mapping support
for vhost-user backends, enabling backends to dynamically request memory
mappings and unmappings during runtime through the new
VHOST_USER_BACKEND_SHMEM_MAP/UNMAP protocol messages.
This feature benefits various VIRTIO devices that require dynamic shared
memory management, including virtiofs (for DAX mappings), virtio-gpu
(for resource sharing), and the recently standardized virtio-media.
The implementation introduces a QOM-based architecture for managing
shared memory lifecycle:
- VirtioSharedMemoryMapping: an intermediate object that manages
individual memory mappings by acting as generic container for regions
declared in any vhost-user device type
- Dynamic Mapping: backends can request mappings via SHMEM_MAP messages,
with the frontend creating MemoryRegions from the provided file
descriptors and adding them as subregions
When a SHMEM_MAP request is received, the frontend:
1. Creates VirtioSharedMemoryMapping to manage the mapping lifecycle
2. Maps the provided fd with memory_region_init_ram_from_fd()
3. Creates a MemoryRegion backed by the mapped memory
4. Adds it as a subregion of the appropiate VIRTIO Shared Memory Region
The QOM reference counting ensures automatic cleanup when mappings are
removed or the device is destroyed.
This patch also includes:
- VHOST_USER_GET_SHMEM_CONFIG: a new frontend request allowing generic
vhost-user devices to query shared memory configuration from backends
at device initialization, enabling the generic vhost-user-device
frontend to work with any backend regardless of specific shared memory
requirements.
The implementation has been tested with rust-vmm based backends.
Albert Esteve (7):
vhost-user: Add VirtIO Shared Memory map request
vhost_user.rst: Align VhostUserMsg excerpt members
vhost_user.rst: Add SHMEM_MAP/_UNMAP to spec
vhost_user: Add frontend get_shmem_config command
vhost_user.rst: Add GET_SHMEM_CONFIG message
qmp: add shmem feature map
vhost-user-device: Add shared memory BAR
docs/interop/vhost-user.rst | 104 +++++++++
hw/virtio/vhost-user-base.c | 46 +++-
hw/virtio/vhost-user-test-device-pci.c | 38 ++-
hw/virtio/vhost-user.c | 269 ++++++++++++++++++++++
hw/virtio/virtio-qmp.c | 3 +
hw/virtio/virtio.c | 201 ++++++++++++++++
include/hw/virtio/vhost-backend.h | 10 +
include/hw/virtio/vhost-user.h | 1 +
include/hw/virtio/virtio.h | 137 +++++++++++
include/system/memory.h | 13 ++
subprojects/libvhost-user/libvhost-user.c | 70 ++++++
subprojects/libvhost-user/libvhost-user.h | 54 +++++
12 files changed, 941 insertions(+), 5 deletions(-)
--
2.52.0
