Subject: Re: Some more 4xx exception fixes

From: David Gibson <[email-masked]>
Date: Thu, 13 Sep 2001 17:51:39 +1000

On Wed, Sep 12, 2001 at 11:42:24AM -0400, Dan Malek wrote:
>
> David Gibson wrote:
>
> > The problem was that the DSI handler would not call do_page_fault()
> > for zone protection faults which were writes
>
> The real problem is the zone protection isn't set up properly
> on the kernel space.  The normal logic of the DSI will work
> correctly without testing specifically for a zone protection error
> if the zone is properly configured.  I noticed this error the other
> day while fixing the other MMU problems, but it wasn't detrimental
> to simply making the kernel run, so I'm fixing it today.

Sorry, can you elaborate on that?  I don't see how we can detect the
case of user writes to kernel (writable) pages without checking the
ESPRN_DIZ bit.

> > The wart is that the ISI handler passed SRR1 (i.e. saved MSR) to
> > do_page_fault(), whereas the comment above do_page_fault() says that
> > do_page_fault() should be passed 0 for instruction faults on 4xx.
>
> I guess....this is left over from a common exception handler I
> suppose.  The only bit position tested is ESR_DST, which for the
> last few years has always been reserved and zero in the MSR.  This
> is a larger problem on other processors, where we overload this
> code into the fault handler with bits that do mean something......

No argument there, but it seems better to make the exception handler
match the documentation on do_page_fault(), given that I can't see any
disadvantage to the changed version.

--
David Gibson			| For every complex problem there is a
[email-masked]	| solution which is simple, neat and
				| wrong.  -- H.L. Mencken
http://www.ozlabs.org/people/dgibson

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