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