On Wed, Sep 10, 2025 at 1:54 PM Albert Esteve <aesteve@redhat.com> wrote:
>
> Hi all,
>
> v7->v8
> - Unified VhostUserShmemObject and VirtioSharedMemoryMapping
> - Refined shmem_obj lifecycle by transferring ownership
> - Other small improvements
> v6->v7
> - Fixed vhost_user_shmem_object_new to use
> memory_region_init_ram_from_fd as before
> v5->v6
> - Added intermediate QOM object to manage shared MemoryRegion lifecycle
> with reference counting, and automatic cleanup
> - Resolved BAR conflict, change from 2 to 3 to avoid conflict with
> `modern-pio-notify=on`
> - Added SHMEM_CONFIG validation in vhost-user-test
> - Changed VirtSharedMemory -> VirtioSharedMemory
> - Changed MappedMemoryRegion -> VirtioSharedMemoryMapping
> - Changed from heap-allocated MemoryRegion *mr to embedded MemoryRegion
> mr in VirtioSharedMemory structure to eliminate memory leaks and
> simplify cleanup
> - Fixed VirtioSharedMemory initialization and cleanup with
> memory_region_init() and object_unparent()
> - Other minor fixes, typos, and updates.
>
> 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.
Small bump to avoid this patch series falling too much.
>
> The implementation has been tested with rust-vmm based backends and
> includes SHMEM_CONFIG QTest validation.
>
> 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 | 101 +++++++++
> hw/virtio/vhost-user-base.c | 47 +++-
> hw/virtio/vhost-user-device-pci.c | 34 ++-
> hw/virtio/vhost-user.c | 249 +++++++++++++++++++++-
> hw/virtio/virtio-qmp.c | 3 +
> hw/virtio/virtio.c | 198 +++++++++++++++++
> include/hw/virtio/vhost-backend.h | 10 +
> include/hw/virtio/vhost-user.h | 1 +
> include/hw/virtio/virtio.h | 138 ++++++++++++
> subprojects/libvhost-user/libvhost-user.c | 70 ++++++
> subprojects/libvhost-user/libvhost-user.h | 54 +++++
> 11 files changed, 898 insertions(+), 7 deletions(-)
>
> --
> 2.49.0
>