Re: [PATCH v14 0/7] vhost-user: Add SHMEM_MAP/UNMAP requests

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Mar 05, 2026 at 09:06:20AM +0100, Stefano Garzarella wrote:
> On Wed, Mar 04, 2026 at 05:52:16PM +0100, Albert Esteve wrote:
> > Hi all,
> 
> Thanks!
> 
> This is now fully reviewed, Michael can we queue it?
> 
> Thanks,
> Stefano


yes, I tagged it already.

> > 
> > v13->v14
> > - Switched F_SHMEM id to 21 to avoid collision after rebasing
> > - Fixed all occurrences of shmem->mr.size to memory_region_size()
> > - Other small fixes following reviews from previous version
> > 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.
> > 
> > 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    |  42 +++-
> > hw/virtio/vhost-user.c                    | 274 ++++++++++++++++++++++
> > 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                | 136 +++++++++++
> > include/system/memory.h                   |   2 +-
> > subprojects/libvhost-user/libvhost-user.c |  70 ++++++
> > subprojects/libvhost-user/libvhost-user.h |  54 +++++
> > system/memory.c                           |  14 ++
> > 13 files changed, 951 insertions(+), 6 deletions(-)
> > 
> > -- 
> > 2.52.0
> >