Hi all, I am trying to understand how vfio enables DMA from user space memory. I would appreciate any help on this.
Suppose we have a system with x86 architecture and an IOMMU. When a user space driver in that system wants to ask from a PCI device to perform DMA from user space memory, it has to register that memory with VFIO_IOMMU_MAP_DMA ioctl. What are the restrictions that this user space memory has to meet? How are the DMA memory limitations met? Is this totally arranged by vfio? Or is it a responsibility of the user space process (eg. use hugepages)? I had a conversation on the SPDK mailing list about this. SPDK is a storage framework running entirely in user space and uses vfio to control the PCI storage devices. This is the relevant email: https://lists.01.org/pipermail/spdk/2018-November/002733.html I am a little bit confused about the purpose of hugepages in SPDK and whether they are related to vfio. To summarize, I am trying to find the answer to the following questions: Is there any constraint about the DMA memory buffers passed to vfio? Is it possible to pass a buffer allocated with malloc? Or is it necessary to use hugepages which by design serve all the DMA memory limitations (pinned, non-swappable, physically contiguous)? Thanks, Nikos _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://www.redhat.com/mailman/listinfo/vfio-users
