[PATCH 0/4] cover-letter: Allow MMIO regions to be exported through dmabuf

[Wei Lin Guay]

From: Wei Lin Guay <wguay at meta.com>

This is another attempt to revive the patches posted by Jason
Gunthorpe and Vivek Kasireddy, at
https://patchwork.kernel.org/project/linux-media/cover/0-v2-472615b3877e+28f7-vfio_dma_buf_jgg@nvidia.com/
https://lwn.net/Articles/970751/

In addition to the initial proposal by Jason, another promising
application is exposing memory from an AI accelerator (bound to VFIO)
to an RDMA device. This would allow the RDMA device to directly access
the accelerator's memory, thereby facilitating direct data
transactions between the RDMA device and the accelerator.

Below is from the text/motivation from the orginal cover letter.

dma-buf has become a way to safely acquire a handle to non-struct page
memory that can still have lifetime controlled by the exporter. Notably
RDMA can now import dma-buf FDs and build them into MRs which allows for
PCI P2P operations. Extend this to allow vfio-pci to export MMIO memory
from PCI device BARs.

This series supports a use case for SPDK where a NVMe device will be owned
by SPDK through VFIO but interacting with a RDMA device. The RDMA device
may directly access the NVMe CMB or directly manipulate the NVMe device's
doorbell using PCI P2P.

However, as a general mechanism, it can support many other scenarios with
VFIO. I imagine this dmabuf approach to be usable by iommufd as well for
generic and safe P2P mappings.

This series goes after the "Break up ioctl dispatch functions to one
function per ioctl" series.

v2:
 - Name the new file dma_buf.c
 - Restore orig_nents before freeing
 - Fix reversed logic around priv->revoked
 - Set priv->index
 - Rebased on v2 "Break up ioctl dispatch functions"
v1: https://lore.kernel.org/r/0-v1-9e6e1739ed95+5fa-vfio_dma_buf_jgg@nvidia.com
Cc: linux-rdma at vger.kernel.org
Cc: Oded Gabbay <ogabbay at kernel.org>
Cc: Christian König <christian.koenig at amd.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Leon Romanovsky <leon at kernel.org>
Cc: Maor Gottlieb <maorg at nvidia.com>
Cc: dri-devel at lists.freedesktop.org
Signed-off-by: Jason Gunthorpe <jgg at nvidia.com>

Jason Gunthorpe (3):
  vfio: Add vfio_device_get()
  dma-buf: Add dma_buf_try_get()
  vfio/pci: Allow MMIO regions to be exported through dma-buf

Wei Lin Guay (1):
  vfio/pci: Allow export dmabuf without move_notify from importer

 drivers/vfio/pci/Makefile          |   1 +
 drivers/vfio/pci/dma_buf.c         | 291 +++++++++++++++++++++++++++++
 drivers/vfio/pci/vfio_pci_config.c |   8 +-
 drivers/vfio/pci/vfio_pci_core.c   |  44 ++++-
 drivers/vfio/pci/vfio_pci_priv.h   |  30 +++
 drivers/vfio/vfio_main.c           |   1 +
 include/linux/dma-buf.h            |  13 ++
 include/linux/vfio.h               |   6 +
 include/linux/vfio_pci_core.h      |   1 +
 include/uapi/linux/vfio.h          |  18 ++
 10 files changed, 405 insertions(+), 8 deletions(-)
 create mode 100644 drivers/vfio/pci/dma_buf.c

--
2.43.5