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
>