Better Intel IOMMU Debugging Is On The Way, ARM IOMMU Working On Faster Performance

Written by Michael Larabel in Virtualization on 27 October 2018 at 06:41 AM EDT. 2 Comments
Better/easier debugging for Intel VT-d IOMMU is on the way to help iron out any lingering issues with virtualization for directed I/O.

The Intel IOMMU driver code is picking up DebugFS support for exposing more data useful to developers when this support is enabled. Via /sys/kernel/debug/intel_iommu/, the IOMMU registers, internal context, and individual table entries are exposed for assisting developers in debugging any issues. The INTEL_IOMMU_DEBUG kernel config switch is added for controlling this behavior and on most platforms reading the kernel debugfs data requires root anyhow for not exposing potentially sensitive data.

These internal Intel IOMMU data structures previously weren't exposed nicely to user-space but now will be with Linux 4.20~5.0. This DebugFS support was introduced by the IOMMU PR.

Also worth noting is that this kernel is bringing faster ARM IOMMU performance. The ARM-SMMU driver now uses generic deferred flushing and faster IOVA allocation code. Those ARM IOMMU changes are exposed to bring a "major performance improvement."

Exciting times as always in kernel space.
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