Re: [PATCH v1 00/10] vfio/pci: Allow MMIO regions to be exported through dma-buf

[Benjamin LaHaise <bcrl@kvack.org>]

FYI: this entire patch series was rejected as spam by large numbers of
linux-mm subscribers using @gmail.com email addresses.

		-ben (owner-linux-mm)

On Mon, Aug 04, 2025 at 04:00:35PM +0300, Leon Romanovsky wrote:
> Changelog:
> v1:
>  * Changed commit messages.
>  * Reused DMA_ATTR_MMIO attribute.
>  * Returned support for multiple DMA ranges per-dMABUF.
> v0: https://lore.kernel.org/all/cover.1753274085.git.leonro@nvidia.com
> 
> ---------------------------------------------------------------------------
> Based on "[PATCH v1 00/16] dma-mapping: migrate to physical address-based API"
> https://lore.kernel.org/all/cover.1754292567.git.leon@kernel.org series.
> ---------------------------------------------------------------------------
> 
> This series extends the VFIO PCI subsystem to support exporting MMIO regions
> from PCI device BARs as dma-buf objects, enabling safe sharing of non-struct
> page memory with controlled lifetime management. This allows RDMA and other
> subsystems to import dma-buf FDs and build them into memory regions for PCI
> P2P operations.
> 
> The 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. This dmabuf approach can be usable by iommufd as well for generic
> and safe P2P mappings.
> 
> In addition to the SPDK use-case mentioned above, the capability added
> in this patch series can also be useful when a buffer (located in device
> memory such as VRAM) needs to be shared between any two dGPU devices or
> instances (assuming one of them is bound to VFIO PCI) as long as they
> are P2P DMA compatible.
> 
> The implementation provides a revocable attachment mechanism using dma-buf
> move operations. MMIO regions are normally pinned as BARs don't change
> physical addresses, but access is revoked when the VFIO device is closed
> or a PCI reset is issued. This ensures kernel self-defense against
> potentially hostile userspace.
> 
> The series includes significant refactoring of the PCI P2PDMA subsystem
> to separate core P2P functionality from memory allocation features,
> making it more modular and suitable for VFIO use cases that don't need
> struct page support.
> 
> -----------------------------------------------------------------------
> The series is based originally on
> https://lore.kernel.org/all/20250307052248.405803-1-vivek.kasireddy@intel.com/
> but heavily rewritten to be based on DMA physical API.
> -----------------------------------------------------------------------
> The WIP branch can be found here:
> https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/log/?h=dmabuf-vfio-v1
> 
> Thanks
> 
> Leon Romanovsky (8):
>   PCI/P2PDMA: Remove redundant bus_offset from map state
>   PCI/P2PDMA: Separate the mmap() support from the core logic
>   PCI/P2PDMA: Simplify bus address mapping API
>   PCI/P2PDMA: Refactor to separate core P2P functionality from memory
>     allocation
>   PCI/P2PDMA: Export pci_p2pdma_map_type() function
>   types: move phys_vec definition to common header
>   vfio/pci: Enable peer-to-peer DMA transactions by default
>   vfio/pci: Add dma-buf export support for MMIO regions
> 
> Vivek Kasireddy (2):
>   vfio: Export vfio device get and put registration helpers
>   vfio/pci: Share the core device pointer while invoking feature
>     functions
> 
>  block/blk-mq-dma.c                 |   7 +-
>  drivers/iommu/dma-iommu.c          |   4 +-
>  drivers/pci/p2pdma.c               | 154 ++++++++----
>  drivers/vfio/pci/Kconfig           |  20 ++
>  drivers/vfio/pci/Makefile          |   2 +
>  drivers/vfio/pci/vfio_pci_config.c |  22 +-
>  drivers/vfio/pci/vfio_pci_core.c   |  59 +++--
>  drivers/vfio/pci/vfio_pci_dmabuf.c | 390 +++++++++++++++++++++++++++++
>  drivers/vfio/pci/vfio_pci_priv.h   |  23 ++
>  drivers/vfio/vfio_main.c           |   2 +
>  include/linux/dma-buf.h            |   1 +
>  include/linux/pci-p2pdma.h         | 114 +++++----
>  include/linux/types.h              |   5 +
>  include/linux/vfio.h               |   2 +
>  include/linux/vfio_pci_core.h      |   4 +
>  include/uapi/linux/vfio.h          |  25 ++
>  kernel/dma/direct.c                |   4 +-
>  mm/hmm.c                           |   2 +-
>  18 files changed, 715 insertions(+), 125 deletions(-)
>  create mode 100644 drivers/vfio/pci/vfio_pci_dmabuf.c
> 
> -- 
> 2.50.1
> 

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