Re: Some more 4xx exception fixes

On Wed, Sep 12, 2001 at 11:42:24AM -0400, Dan Malek wrote:

David Gibson wrote:

quoted

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.

quoted

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
david@gibson.dropbear.id.au	| solution which is simple, neat and
				| wrong.  -- H.L. Mencken
http://www.ozlabs.org/people/dgibson


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