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

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Message-Id: <20061206.164616.74731030.davem@davemloft.net>
Date:	Wed, 06 Dec 2006 16:46:16 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	mattjreimer@...il.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: D-cache aliasing issue in cow_user_page

From: "Matt Reimer" <mattjreimer@...il.com>
Date: Wed, 6 Dec 2006 13:19:41 -0800

> On 12/5/06, David Miller <davem@...emloft.net> wrote:
> > From: "Matt Reimer" <mattjreimer@...il.com>
> > Date: Tue, 5 Dec 2006 16:57:12 -0800
> >
> > > 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() ?
> >
> > No.  He is only solving a problem that occurs on HIGHMEM
> > configurations on systems which can have D-cache aliasing
> > issues.
> 
> Are you sure? James specifically mentions "non-highmem architectures,"
> and "all architectures with coherence issues," which would seem to
> include ARM (which is my concern).
> 
> For your convenience I quote the whole commit message below.

Ok, I see.

He's providing it an alternative way to solve the coherency
issues.

You can still solve it the traditional way via cache flushing
in flush_dcache_page() and {copy,clear}_user_page().
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