Re: problems on D-cache alias in 2.4.22

[Ralf Baechle <ralf@linux-mips.org>]

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