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Date:   Thu, 20 Sep 2018 21:52:04 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Andrew Lunn <andrew@...n.ch>, Arnd Bergmann <arnd@...db.de>,
        Eric Biggers <ebiggers@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Neves <sneves@....uc.pt>,
        Andrew Lutomirski <luto@...nel.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>
Subject: Re: [PATCH net-next v5 02/20] zinc: introduce minimal cryptography library



> On Sep 20, 2018, at 9:30 PM, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
> 
>> On 20 September 2018 at 21:15, Jason A. Donenfeld <Jason@...c4.com> wrote:
>> Hi Andy,
>> 
>>> On Fri, Sep 21, 2018 at 5:23 AM Andy Lutomirski <luto@...capital.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.

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