Re: [PATCH net-next v5 02/20] zinc: introduce minimal cryptography library

From: Jason A. Donenfeld
Date: Fri Sep 21 2018 - 00:16:05 EST

Hi Andy,

On Fri, Sep 21, 2018 at 5:23 AM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> At the risk on suggesting something awful: on x86_64, since we turn preemption off for simd, it wouldnât be *completely* insane to do the crypto on the irq stack. It would look like:
> kernel_fpu_call(func, arg);
> And this helper would disable preemption, enable FPU, switch to the irq stack, call func(arg), disable FPU, enable preemption, and return. And we can have large IRQ stacks.
> I refuse to touch this with a ten-foot pole until the lazy FPU restore patches land.

Haha. That's fun, and maybe we'll do that at some point, but I have
some other reasons too for being on a workqueue now.

> All that being said, why are these frames so large? It sounds like something may be spilling that ought not to.

They're not. Well, they're not anymore. I had a silly thing before
like "u8 buffer[1 << 12]" in some debugging code, which is what
prompted the ccflag-y addition. I cleaned up the mistakes like that
and frames are now reasonable everywhere. Non-issue.