Re: [PATCH net-next v5 02/20] zinc: introduce minimal cryptography library
From: Andy Lutomirski
Date: Fri Sep 21 2018 - 00:52:10 EST
> On Sep 20, 2018, at 9:30 PM, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>> On 20 September 2018 at 21:15, Jason A. Donenfeld <Jason@xxxxxxxxx> wrote:
>> 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.
> 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.