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

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Message-ID: <CAHmME9rF=FfOf-_EOB-BeT-BM=B9Q9YzFAoUimaPiM2RKb5sGA@mail.gmail.com>
Date:   Fri, 21 Sep 2018 06:15:46 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andrew Lunn <andrew@...n.ch>, Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        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

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.

>
> 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.

Jason