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

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Message-Id: <20061019004118.37741cad.akpm@osdl.org>
Date:	Thu, 19 Oct 2006 00:41:18 -0700
From:	Andrew Morton <akpm@...l.org>
To:	David Miller <davem@...emloft.net>
Cc:	dmonakhov@...nvz.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] mm:D-cache aliasing issue in cow_user_page

On Thu, 19 Oct 2006 00:22:37 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> > > Architectures typically take care of this in copy_user_page() and
> > > clear_user_page().  The absolutely depend upon those two routines
> > > being used for anonymous pages, and handle the D-cache issues there.
> > 
> > Only anonymous pages?  There are zillions of places where we modify
> > pagecache without a flush, especially against the blockdev mapping (fs
> > metadata).
> 
> It's cpu stores that matter, not device DMA and the like, and we have
> flush_dcache_page() calls in the correct spots.  You can see that
> we take care of this even in places such as the loop driver :-)

grep b_data fs/*/*.c

All of them ;)

It's possible to mmap /dev/hda, but it's a rather odd thing to do (INND
can do it, but not a live filesystem).

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