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

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Message-ID: <20190821021741.GB32710@infradead.org>
Date:   Tue, 20 Aug 2019 19:17:41 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     guoren@...nel.org
Cc:     arnd@...db.de, linux-kernel@...r.kernel.org,
        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

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.  Kernel code must
use the get_unaligned* / put_unaligned* helpers for that.