Hi all,

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

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

>
>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
>

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
> >