Linux 5.2 IOMMU Changes Allow For More Flexible Intel VT-d Alternative To SR-IOV
Written by Michael Larabel in Linux Kernel on 13 May 2019 at 12:01 PM EDT. 2 Comments
LINUX KERNEL --
Merged today for the Linux 5.2 kernel are the IOMMU changes that contain some interesting Intel additions.

With the IOMMU changes for Linux 5.2 is AUX (auxiliary) domain support for the kernel's IOMMU API and necessary Intel VT-d driver support. What this "AUX domain" support allows is handling of multiple DMA address spaces / domains per PCI device.

Intel has been working on this support for multiplexing these PCI devices between hosts and (KVM) guests in a "more flexible way than supported by SR-IOV." SR-IOV is the PCI Express standard for sharing a PCIe device with a virtual machine. The VT-d bits tie in with their new VT-d Scalable Mode capabilities. Scalable IOV is designed to allow highly-scalable and high performance sharing of I/O hardware between VMs/containers/processes.

More details on this work via the earlier patches that are now in the mainline kernel with Linux 5.2. Once everything is plumbed through the stack with this IOMMU auxiliary domain support, it looks like this work could help for example Radeon users for those interested in GPU virtualization but where SR-IOV generally isn't supported on their consumer cards.
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