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

[Andy Lutomirski]

> On Sep 20, 2018, at 9:30 PM, Ard Biesheuvel <ard.biesheu...@linaro.org> wrote:
> 
>> On 20 September 2018 at 21:15, Jason A. Donenfeld <ja...@zx2c4.com> wrote:
>> Hi Andy,
>> 
>>> On Fri, Sep 21, 2018 at 5:23 AM Andy Lutomirski <l...@amacapital.net> wrote:
>>> At the risk on suggesting something awful: on x86_64, since we turn 
>>> preemption off for simd, it wouldn’t 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.
>> 
> 
> Kernel mode crypto is callable from any context, and SIMD can be used
> in softirq context on arm64 (and on x86, even from hardirq context
> IIRC if the interrupt is taken from userland), in which case we'd
> already be on the irq stack.

The x86_64 irq stack handles nesting already.