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

Benjamin LaHaise
2025-08-04T14:10:38Z

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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