Microsoft Contributes Para-Virtualized IOMMU Hyper-V Driver For Linux

Microsoft is contributing a new kernel driver for the upcoming Linux 7.4 cycle. Queued up into the IOMMU subsystem's "-next" branch is a new para-virtualized IOMMU driver for benefiting Linux guest VMs running on Microsoft's Hyper-V virtualization platform. In addition to the excitement of AMD's PerfOpt feature being in the IOMMU next Git branch for Linux 7.4, adding to the IOMMU fun for Linux 7.4 is this new Microsoft para-virtualized IOMMU driver for Hyper-V, which is enabled via the new HYPERV_PVIOMMU Kconfig option. The Microsoft para-virtualized IOMMU driver allows for Linux guests on Hyper-V to enjoy in-kernel DMA protection for devices assigned to the guest. This driver also allows for device assignment to the guest user-space such as via VFIO. This para-virtualized IOMMU for Hyper-V works on both Intel VT-d and AMD IOMMU enabled systems. This has been validated with testing NVMe devices assigned to the guest and on the Intel side their DSA accelerator devices were also tested in assigning to guest Linux VMs. This "hv-iommu-guest" driver has been a long time coming with the original request for comments (RFC) patches on this support dating back to December 2023. Linux 7.4 stable should be out around the end of December, or three years after those patches first appeared. The code is in the next Git branch until the Linux 7.4 merge window opens later this month.