Re: dcbz works on 862 everywhere!

[Dan Malek <dan@embeddededge.com>]

Joakim Tjernlund wrote:

>
> I think it makes the "copy DAR to MD_EPN" part in the DTLB error handler needless.
> Anyway it works with and without that part.

No, you need to leave that there as well.  Read the comment.....

If it appears to "work" for you, what happens is you have a DTLB Error
immediately following a DTLB miss (the common case lots of the time), so
the MD_EPN just happens to contain the proper information.  When you generate
the case where a DTLB Error does not match a previous DTLB miss, you will
end up tracking down the wrong PTEs.  Even in this case it is likely to
appear things work correctly, but they do not.  There is one case with the dcbi
where there is no proper operation of the code, so it was necessary to solve
the problem another way.

This is exactly why people are telling you to carefully generate test cases
the prove an error exists 100% of the time, and that your modifications
properly correct the condition 100% of the time.  When you run something
like Linux you get pathological cases that do not exercise all conditions
with a particular configurations, or you could be generating errors that
are not precisely tested as failure conditions.

Thanks.


	-- Dan


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