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Date: Tue, 18 May 2004 21:50:55 +0200
From: Ralf Baechle <ralf@linux-mips.org>
To: Peter Horton <pdh@colonel-panic.org>
Cc: Jun Sun <jsun@mvista.com>, Bob Breuer <bbreuer@righthandtech.com>,
	linux-mips@linux-mips.org
Subject: Re: problems on D-cache alias in 2.4.22
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On Tue, May 18, 2004 at 08:10:19PM +0100, Peter Horton wrote:

> The kernel maps the page cache page into user space ... BANG! possible
> D-cache alias.
> 
> The kernel doesn't bother flushing the page cache page from the D-cache
> as it's never accessed at it's page cache address.

It is - after all the driver is copying the data to there.  The same
problem also exists in the ramdisk driver and there it has been fixed
properly, it seems.

> The current fix in the Cobalt patches (2.4 & 2.6) just flushes the read
> data out of the D-cache after every IDE insw()/insl(). This is the least
> intrusive fix.
> 
> Some Sparc machines also see this problem.

Carelessly written PIO drivers on any architecture would suffer from this
kind of problem.

  Ralf