On Sat, 1 Sep 2018, Jason A. Donenfeld wrote:

On Sat, Sep 1, 2018 at 2:32 PM Andy Lutomirski [off-list ref] wrote:

quoted

I tend to think the right approach is to merge Jason's code and then
make it better later.  Even with a totally perfect lazy FPU restore
implementation on x86, we'll probably still need some way of dealing
with SIMD contexts.  I think we're highly unlikely to ever a allow
SIMD usage in all NMI contexts, for example, and there will always be
cases where we specifically don't want to use all available SIMD
capabilities even if we can.  For example, generating random numbers
does crypto, but we probably don't want to do *SIMD* crypto, since
that will force a save and restore and will probably fire up the
AVX512 unit, and that's not worth it unless we're already using it for
some other reason.

Also, as Rik has discovered, lazy FPU restore is conceptually
straightforward but isn't entirely trivial :)

Sounds good. I'll move ahead on this basis.

Fine with me.