The x86-64 FPU state is quite large so normally the user task's FPU state is only saved/restored on a task switch. This means that if kernel code wants to use

The x86-64 FPU state is quite large so normally the user task's FPU state is only saved/restored on a task switch. This means that if kernel code wants to use the FPU (which includes the SIMD instructions), it has to explicitly request access and return it when it's done. The functions that do that are the exports being referred to here.