linux-kernel - Re: [PATCH] crypto: lib/chacha20poly1305 - Set SG_MITER

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Date:   Mon, 14 Sep 2020 23:45:53 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>
Subject: Re: [PATCH] crypto: lib/chacha20poly1305 - Set SG_MITER_ATOMIC unconditionally

On Mon, Sep 14, 2020 at 8:30 PM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> There is no reason for the chacha20poly1305 SG miter code to use
> kmap instead of kmap_atomic as the critical section doesn't sleep
> anyway.  So we can simply get rid of the preemptible check and
> set SG_MITER_ATOMIC unconditionally.

So I'd prefer to make SG_MITER_ATOMIC go away entirely, and just
remove the non-atomic case..

A quick grep seems to imply that just about all users set the ATOMIC
bit anyway. I didn't look at everything, but every case I _did_ look
at did seem to set the ATOMIC bit.

So it really did seem like there isn't a lot of reason to have the
non-atomic case, and this flag could go away - not by virtue of the
atomic case going away, but by virtue of the atomic case being the
only actual case.

I mean, I did find one case that didn't set it (cb710-mmc.c), but
pattern-matching to the other mmc cases, that one looks like it
_should_ have set the atomic flag like everybody else did.

Did I miss something?

             Linus