Function request_dynamic_xstate_features 

pub fn request_dynamic_xstate_features() -> Result<(), XstateError>

Request permission for all dynamic XSTATE features.

Some XSTATE features are not permitted by default, because they may require a larger area to save their states than the tranditional 4096-byte area. Instead, the permission for them can be requested via arch_prctl(). https://github.com/torvalds/linux/blob/master/Documentation/arch/x86/xstate.rst

Firecracker requests permission for them by default if available in order to retrieve the full supported feature set via KVM_GET_SUPPORTED_CPUID. https://docs.kernel.org/virt/kvm/api.html#kvm-get-supported-cpuid

Note that requested features can be masked by a CPU template.