On Wed, Jun 11, 2025 at 8:21 AM Alyssa Ross <h...@alyssa.is> wrote: > > Albert Esteve <aest...@redhat.com> writes: > > > Add SHMEM_MAP/_UNMAP request to the vhost-user > > spec documentation. > > > > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com> > > Signed-off-by: Albert Esteve <aest...@redhat.com> > > --- > > docs/interop/vhost-user.rst | 55 +++++++++++++++++++++++++++++++++++++ > > 1 file changed, 55 insertions(+) > > > > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst > > index 436a94c0ee..b623284819 100644 > > --- a/docs/interop/vhost-user.rst > > +++ b/docs/interop/vhost-user.rst > > @@ -350,6 +350,27 @@ Device state transfer parameters > > In the future, additional phases might be added e.g. to allow > > iterative migration while the device is running. > > > > +MMAP request > > +^^^^^^^^^^^^ > > + > > ++-------+---------+-----------+------------+-----+-------+ > > +| shmid | padding | fd_offset | shm_offset | len | flags | > > ++-------+---------+-----------+------------+-----+-------+ > > + > > +:shmid: a 8-bit shared memory region identifier > > + > > +:fd_offset: a 64-bit offset of this area from the start > > + of the supplied file descriptor > > + > > +:shm_offset: a 64-bit offset from the start of the > > + pointed shared memory region > > + > > +:len: a 64-bit size of the memory to map > > + > > +:flags: a 64-bit value: > > + - 0: Pages are mapped read-only > > + - 1: Pages are mapped read-write > > + > > C structure > > ----------- > > > > @@ -375,6 +396,7 @@ In QEMU the vhost-user message is implemented with the > > following struct: > > VhostUserInflight inflight; > > VhostUserShared object; > > VhostUserTransferDeviceState transfer_state; > > + VhostUserMMap mmap; > > }; > > } QEMU_PACKED VhostUserMsg; > > > > @@ -1057,6 +1079,7 @@ Protocol features > > #define VHOST_USER_PROTOCOL_F_XEN_MMAP 17 > > #define VHOST_USER_PROTOCOL_F_SHARED_OBJECT 18 > > #define VHOST_USER_PROTOCOL_F_DEVICE_STATE 19 > > + #define VHOST_USER_PROTOCOL_F_SHMEM 20 > > > > Front-end message types > > ----------------------- > > @@ -1865,6 +1888,38 @@ is sent by the front-end. > > when the operation is successful, or non-zero otherwise. Note that if the > > operation fails, no fd is sent to the backend. > > > > +``VHOST_USER_BACKEND_SHMEM_MAP`` > > + :id: 9 > > + :equivalent ioctl: N/A > > + :request payload: fd and ``struct VhostUserMMap`` > > + :reply payload: N/A > > + > > + When the ``VHOST_USER_PROTOCOL_F_SHMEM`` protocol feature has been > > + successfully negotiated, this message can be submitted by the backends to > > + advertise a new mapping to be made in a given VIRTIO Shared Memory > > Region. > > + Upon receiving the message, the front-end will mmap the given fd into the > > + VIRTIO Shared Memory Region with the requested ``shmid``. A reply is > > + generated indicating whether mapping succeeded. > > Should this be phrased to make it clear replies are only generated in > some cases, like how e.g. VHOST_USER_BACKEND_IOTLB_MSG phrases it? > > If ``VHOST_USER_PROTOCOL_F_REPLY_ACK`` is negotiated, and > back-end set the ``VHOST_USER_NEED_REPLY`` flag, the front-end > must respond with zero when operation is successfully completed, > or non-zero otherwise. >
Right! Thanks for the catch. I will fix it (and the others in your comment) in the next version. BR, Albert. > > + > > + Mapping over an already existing map is not allowed and request shall > > fail. > > request*s* shall fail > > > + Therefore, the memory range in the request must correspond with a valid, > > + free region of the VIRTIO Shared Memory Region. Also, note that mappings > > + consume resources and that the request can fail when there are no > > resources > > + available. > > + > > +``VHOST_USER_BACKEND_SHMEM_UNMAP`` > > + :id: 10 > > + :equivalent ioctl: N/A > > + :request payload: ``struct VhostUserMMap`` > > + :reply payload: N/A > > + > > + When the ``VHOST_USER_PROTOCOL_F_SHMEM`` protocol feature has been > > + successfully negotiated, this message can be submitted by the backends so > > + that the front-end un-mmap a given range (``shm_offset``, ``len``) in the > > un-mmaps? > > > + VIRTIO Shared Memory Region with the requested ``shmid``. Note that the > > + given range shall correspond to the entirety of a valid mapped region. > > + A reply is generated indicating whether unmapping succeeded. > > + > > .. _reply_ack: > > > > VHOST_USER_PROTOCOL_F_REPLY_ACK > > -- > > 2.49.0
