Re: [PATCH 1/4] x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state

[Peter Zijlstra]

On Sun, Jan 17, 2021 at 10:20:38PM -0800, Andy Lutomirski wrote:

>  - Code that wants MMX doesn't want need MXCSR or FCW initialized.
>    _mmx_memcpy(), for example, can run before CR4.OSFXSR gets set, and
>    initializing MXCSR will fail.

> +#define KFPU_MMX	0		/* nothing gets initialized */

This... why is that correct?