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

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 23 Jul 2025 16:00:01 +0300
Leon Romanovsky <leon@kernel.org> wrote:

> From: Leon Romanovsky <leonro@nvidia.com>
> 
> ---------------------------------------------------------------------------
> Based on blk and DMA patches which will be sent during coming merge window.
> ---------------------------------------------------------------------------
> 
> 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.

I think this will eventually enable DMA mapping of device MMIO through
an IOMMUFD IOAS for the VM P2P use cases, right?  How do we get from
what appears to be a point-to-point mapping between two devices to a
shared IOVA between multiple devices?  I'm guessing we need IOMMUFD to
support something like IOMMU_IOAS_MAP_FILE for dma-buf, but I can't
connect all the dots.  Thanks,

Alex