We currently use pub(crate) const FP_TAG_WORD_DEFAULT: u8 = 0xff; // each 8 of x87 fpu registers is empty which is incorrect (at least for kvm), which uses abridged format (FXSAVE, not FSAVE), so we should set this to 0x00 to indicate empty, instead of 0xff.

See:
https://docs.kernel.org/virt/kvm/api.html#kvm-get-fpu
https://www.felixcloutier.com/x86/fxsave