Need Eager FPU
Historically x86 has used a lazy FPU that restores the FPU registers in the context a #NM handler based on when the FPU is first used after a context switch. It turns out that through speculative execution it is possible to read values out of the FPU before the #NM takes effect. An eager FPU restore defeats this side channel. See CVE-2018-3665.