Gentle ping on this series incase it got lost in the noise :)
On Tue, Aug 25, 2026 at 10:00 PM Naman Gulati <[email protected]> wrote:
>
> This series extends the vfio-user protocol specification to allow
> servers to pass multiple file descriptors for different sparse memory
> areas to be mmap'ed within a single device region.
>
> This extension is intended for exposing paravirtualized PCI devices via
> a vfio-user server that may have multiple unique sub-regions in a BAR
> backed by some mmap'able buffers sourced from distinct file descriptors.
>
> This change introduces a new capability:
> VFIO_REGION_INFO_CAP_SPARSE_MMAP_FDS
>
> Unlike VFIO_REGION_INFO_CAP_SPARSE_MMAP (which maps all sparse areas
> from a single open file descriptor), this new capability defines an
> array of sparse mmap areas where each area contains an index into the
> array of file descriptors.
>
> When all sparse areas share a single file descriptor, servers may
> continue to emit VFIO_REGION_INFO_CAP_SPARSE_MMAP and send exactly one
> file descriptor in SCM_RIGHTS for backwards compatibility with older
> clients.
>
> The extensions in this series also lays the groundwork to make use of
> the in-development series [1] extending vfio-pci to return distinct
> dmabuf FDs for discrete regions of a device's BAR. A vfio-user server
> may choose to return dmabuf FDs for various regions of a device's BAR to
> map a vfio passthrough device into the guest, in order to retain control
> of the device and be able to revoke mappings passed to the VM.
>
> libvfio-user server side changes WIP on github [2].
>
>
> [1] https://lore.kernel.org/all/[email protected]
> [2] https://github.com/NamanGulati/libvfio-user/tree/multi-region-fd
>
> ---
> Changes from RFC:
> - Refactored the get_region_info callback to keep vbasedev constant
> and take in a VFIORegionFDs* out parameter to store the received fds.
> - Link to RFC:
> https://lore.kernel.org/qemu-devel/[email protected]
> ---
>
> Naman Gulati (3):
> vfio-user: add multi-fd region mmap capability
> vfio: mmap sparse regions backed by multiple FDs
> vfio-user: implement client support for multi-fd region mmap
>
> docs/interop/vfio-user.rst | 71 +++++++++++++++++++++++++++++++++--
> hw/vfio-user/device.c | 66 ++++++++++++++++++++++++++++++--
> hw/vfio-user/protocol.h | 20 ++++++++++
> hw/vfio/device.c | 49 ++++++++++++++----------
> hw/vfio/region.c | 41 ++++++++++++++++----
> hw/vfio/vfio-region.h | 8 ++++
> include/hw/vfio/vfio-device.h | 32 ++++++++++++++--
> 7 files changed, 249 insertions(+), 38 deletions(-)
>
> --
> 2.55.0.860.g4b6b3295ed-goog
>
