Linux 5.14 To Support XMM Fast Hypercalls For Hyper-V On KVM

With the KVM code set to be merged in the coming weeks for the Linux 5.14 kernel, support for fast XMM hypercalls is coming for its Hyper-V guest support in allowing for some performance benefits.

Microsoft Hyper-V's hypercall interface - for the calling mechanism into guests - supports the notion of XMM fast hypercalls. The XMM fast hypercall support allows for some calls to enjoy improved performance. This fast hypercalls interface makes use of six XMM registers compared to otherwise the maximum of two general purpose registers for hypercalls.

The XMM fast hypercalls details are outlined via the Microsoft documentation.

Amazon engineers for Linux 5.14 have contributed support for advertising XMM fast hypercall support to Hyper-V guests within KVM. The necessary patches were queued and thus the feature now advertised with the material in kvm.git's "-next" branch. Amazon is planning on contributing more Linux kernel patches for other hypercall interfaces that make use of this functionality moving forward.