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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 30, 2025 at 01:58:46PM -0600, Alex Williamson wrote: > On Wed, 23 Jul 2025 16:00:01 +0300 > Leon Romanovsky wrote: > > > From: Leon Romanovsky > > > > --------------------------------------------------------------------------- > > 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? This is the plan > How do we get from > what appears to be a point-to-point mapping between two devices to a > shared IOVA between multiple devices? You have it right below, it is a point to point mapping between the vfio device and the iommufd. > I'm guessing we need IOMMUFD to support something like > IOMMU_IOAS_MAP_FILE for dma-buf, 1) The dma phys series which needs more work 2) This series to get basic 'movable' DMABUF support in VFIO 3) Add 'revokable' as a DMABUF concept and implement it with mlx5 and vfio 4) Add some way to get the phys_addr list from the DMABUF 5) IOMMU_IOAS_MAP_FILE using a revokable attachment and the phys_addr list. When VFIO does FLR the iommufd can remove the IOPTEs and then put them back when FLR is done. It is not so much more code, but I think every step will take a lot of work to get agreements. Then we reuse all of the above with some tweaks for the CC problems too. Jason