Hello everyone This is a Request For Comment (RFC) describing a new testing infra called iommutests. It is motivated by interest expressed during the "IO Page Fault for all" [1] talk in LPC 2024 [2]. At the end of that presentation in the "VFIO/IOMMU/PCI MC" microconference, There was a clear "yes please" after asking if it made sense to have an infrastructure that could evaluate the full spectrum of IOMMU interactions — from host software to IOMMU in hardware and in emulated environments. What is iommutests? -------------------- The primary goal of iommutests [3] is to provide a modular framework to test IOMMU-mediated Direct Memory Access (DMA). It is meant to run PASS/NO_PASS tests for the interaction between kernel subsystems and hardware/virtual devices. All this in the hope of clarifying which IOMMU features are working correctly and which are not. You can find the project in github : https://github.com/SamsungDS/iommutests * Test Orchestration: This component is implemented in pytest [4], a testing framework where tests can be parametrized, filtered and implemented concisely and easily. Additionally, pyudev [5] is employed for device enumeration and monitoring, as well as querying device properties and attributes. * Test Executables: For the creation and execution of tests, iommutests leans heavily on libvfn [6], a zero-dependency C library designed for interacting with PCIe-based devices from user-space using the Linux kernel user API. The libvfn library can be used to abstract away common lower-level interactions which can then be re-used through out. A Working Demonstration ----------------------- To better illustrate how everything fits together, There’s a demo script [7], with some demo notes [8] explaining the setup and output. It does the following: 1. Sets up a custom qemu [9] virtual machine environment using a custom test device. 2. Builds both libvfn and iommutests. 3. Runs a pair of example tests (one of them always fails to show how how that would look like) This demo shows how everything comes together to give the pass/no-pass IOMMU testing results. It is there for anyone interested in trying it out or contributing. To run it, you need to pass it a local ssh key and linux kernel compiled with VFIO support Custom qemu device: pci-ats-testdev ------------------------------------- To support IOMMU testing under qemu, the pci-ats-testdev [10] (different from pci-testdev [11]) was used to emulate DMA transactions. It is a full fledged pci device capable of executing emulated DMA accesses. It was originally intended to test Linux kernel interactions with devices that had a working Address Translation Cache (ATC) but can become a platform capable of testing anything PCI/IOMMU related if needed. Feedback -------- This is a first draft, and many implementation details are still open to refinement. I would appreciate your thoughts on any part of the project — its design, scope, implementation language choices, or usability. These are however some of the questions that are still outstanding from my POV: Q1: Beyond binary testing: Would iommutests be used for something other than pass/no-pass tests? Like performance? Stress testing? Q2: Kernel Integration: Should iommutests interact with the already existing IOMMU linux kernel unit tests? Since it is an orchestration framework, then it can execute the unit tests in some way. This could actually be the next step, if found useful. Thanks for your time Best regards, -- Joel Granados [1] https://www.youtube.com/watch?v=UFrAjJ5TUf4 [2] https://lpc.events/event/18/timetable/#20240918 [3] https://github.com/SamsungDS/iommutests [4] https://docs.pytest.org/en/stable/ [5] https://github.com/pyudev/pyudev [6] https://github.com/SamsungDS/libvfn [7] https://github.com/SamsungDS/iommutests/blob/master/docs/demo0_debian.sh [8] https://github.com/SamsungDS/iommutests/blob/master/docs/demo0.md [9] https://github.com/Joelgranados/qemu/tree/pcie-testdev [10] https://github.com/Joelgranados/qemu/blob/pcie-testdev/hw/misc/pcie-ats-testdev.c [11] https://github.com/Joelgranados/qemu/blob/pcie-testdev/hw/misc/pci-testdev.c PS: Apologies for the long CC list. I always try to include the ppl that I think will be interested, but its not always easy to know who you are :). In this case, you are included because you appear as "M" under a subsystem that contains the string "IOMMU" in the MAINTAINERS file. Feel free to shoot me a mail if you don't want to be included in the future, I'll try my best to remove you.
