AMD Posts Latest VNMI Patches For The Linux Kernel

Written by Michael Larabel in AMD on 29 August 2022 at 06:57 AM EDT. Add A Comment
AMD --
Back in early June AMD engineers began posting support for enabling Virtual NMI on Linux for AMD CPUs with KVM and permitting hardware support. VNMI is expected to finally happen on the AMD side with Zen 4 processors and today they posted their latest revision of this work.

As explained previously in the AMD VNMI patches:
Currently, NMI is delivered to the guest using the Event Injection mechanism. The Event Injection mechanism does not block the delivery of subsequent NMIs. So the Hypervisor needs to track the NMI delivery and its completion (by intercepting IRET) before sending a new NMI.

Virtual NMI (VNMI) allows the hypervisor to inject the NMI into the guest w/o using Event Injection mechanism meaning not required to track the guest NMI and intercepting the IRET.

Intel meanwhile has been supporting Virtual NMI on their processors for years. The AMD VNMI Linux patches do not specifically call out AMD Zen 4 as the feature is being checked solely against a feature bit, but given the timing of these patches that is presumably why we are seeing this work happen now.

This morning the v4 patches were sent out as this AMD VNMI support (including nested VNMI) works its way to the mainline Linux kernel. Given the timing of this latest patch iteration, the earliest we'll see this support mainlined would be the v6.1 cycle with its merge window in October.

Meanwhile as a somewhat related reminder, tonight is an AMD livestream event on YouTube concerning their next-generation Ryzen processors.
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