linux-kernel - Re: [PATCH 3/3] csky: Support kernel non-aligned access

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Date:   Wed, 21 Aug 2019 11:43:51 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-csky@...r.kernel.org, douzhk@...ionalchip.com,
        Guo Ren <ren_guo@...ky.com>
Subject: Re: [PATCH 3/3] csky: Support kernel non-aligned access

Thx Christoph

On Wed, Aug 21, 2019 at 10:17 AM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Tue, Aug 20, 2019 at 08:34:29PM +0800, guoren@...nel.org wrote:
> > From: Guo Ren <ren_guo@...ky.com>
> >
> > We prohibit non-aligned access in kernel mode, but some special NIC
> > driver needs to support kernel-state unaligned access. For example,
> > when the bus does not support unaligned access, IP header parsing
> > will cause non-aligned access and driver does not recopy the skb
> > buffer to dma for performance reasons.
> >
> > Added kernel_enable & user_enable to control unaligned access and
> > added kernel_count  & user_count for statistical unaligned access.
>
> If the NIC drivers requires this it is buggy.
Yes, you are right, but I've no control on their non-upstreamed
drivers. Every time kernel version updated I need to take care of that
issue for them. So just give them a back door in arch/csky and they
could disable it by manual.

> Kernel code must
> use the get_unaligned* / put_unaligned* helpers for that.
Most of ethernet drivers use netdev_alloc_skb_ip_align() to let
hardware deal with unaligned access,
but some NICs couldn't and we may modify kernel's skb_ip_header
parsing code with get_unaligned*/put_unaligned* ?

-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/