netdev - Re: Misalignment, MIPS, and ip

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Message-ID: <CAHmME9qxz6wcOZuurqahXeY6QSF=zz0gH7gY4RZujLAJPNSWBA@mail.gmail.com>
Date:   Thu, 8 Dec 2016 01:29:42 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     David Miller <davem@...emloft.net>
Cc:     Dave Taht <dave.taht@...il.com>, Netdev <netdev@...r.kernel.org>,
        linux-mips@...ux-mips.org, LKML <linux-kernel@...r.kernel.org>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>
Subject: Re: Misalignment, MIPS, and ip_hdr(skb)->version

On Wed, Dec 7, 2016 at 8:52 PM, David Miller <davem@...emloft.net> wrote:
> The only truly difficult case to handle is GRE encapsulation.  Is
> that the situation you are running into?
>
> If not, please figure out what the header configuration looks like
> in the case that hits for you, and what the originating device is
> just in case it is a device driver issue.

My case is my own driver and my own protocol, which uses a 13 byte
header. I can, if absolutely necessary, change the protocol to add
another byte of padding. Or I can choose not to decrypt in place but
rather use a different trick, like overwriting the header during
decryption, though this removes some of the scatterwalk optimizations
when src and dst are the same. Or something else. I wrote the top
email of this thread inquiring about just exactly how bad it is to
call netif_rx(skb) when skb->data is unaligned.