linux-kernel - Re: [PATCH] mm: D-cache aliasing issue in cow_user

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Message-ID: <f383264b0612051657r2b62c7acnf10b2800934ab8b3@mail.gmail.com>
Date:	Tue, 5 Dec 2006 16:57:12 -0800
From:	"Matt Reimer" <mattjreimer@...il.com>
To:	"David Miller" <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: D-cache aliasing issue in cow_user_page

On 12/5/06, David Miller <davem@...emloft.net> wrote:
> From: "Matt Reimer" <mattjreimer@...il.com>
> Date: Mon, 4 Dec 2006 23:38:13 -0800
>
> > In light of James Bottomsley's commit[1] declaring that kmap() and
> > friends now have to take care of coherency issues, is the patch "mm:
> > D-cache aliasing issue in cow_user_page"[2] correct, or could it
> > potentially cause a slowdown by calling flush_dcache_page() a second
> > time (i.e. once in an architecture-specific kmap() implementation, and
> > once in cow_user_page())?
>
> kmap() is a NOP unless HIGHMEM is configured.
>
> Therefore, it cannot possibly take care of D-cache aliasing issues
> across the board.

Right, but isn't he declaring that each architecture needs to take
care of this? So, say, on ARM we'd need to make kunmap() not a NOP and
call flush_dcache_page() ?

Matt
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