From: Paul Mackerras <paulus@au1.ibm.com>
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Message-ID: <16078.1121.582683.336497@argo.ozlabs.ibm.com>
Date: Fri, 23 May 2003 21:22:09 +1000
To: Andrew Morton <akpm@digeo.com>
Cc: "Lothar Wassmann" <LW@KARO-electronics.de>, rmk@arm.linux.org.uk,
       linux-kernel@vger.kernel.org
Subject: Re: [patch] cache flush bug in mm/filemap.c (all kernels >=
 2.5.30(at least))
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Andrew Morton writes:

> filemap_nopage isn't the right place to be doing these things though.
> 
> Given that there was no page at the virtual address before filemap_nopage
> was called I don't think any CPU cache writeback or invalidation need be
> performed.  Perhaps a writeback or invalidate is missing somewhere in the
> unmap paths, or there is a problem in arch/arm somewhere.
> 
> We have a no-op flush_icache_page() in do_no_page(), but I don't know what
> that thing ever did, not what it's doing in there.  (What happens if you
> replace it with a flush_cache_page(vma, address)?)

We used to use flush_icache_page() on ppc/ppc64 to ensure that the
i-cache was consistent with the d-cache and with memory.  It was
needed in do_no_page for the case where the page had just been read in
and the i-cache could have stale data reflecting the previous contents
of the page (the i-cache doesn't snoop on ppc).  But we now do that in
update_mmu_cache.

Paul.
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