>>>>> On Fri, 18 Mar 2005 18:04:37 +1100, Keith Owens <[EMAIL PROTECTED]> said:
Keith> memcpy_mck.S::__copy_user breaks in the prefetch code under these
Keith> conditions :-
Keith> * src is unaligned and
Keith> * dst is near the end of a page and
Keith> * the page after dst is unmapped.
Keith> The loop count in r21 is 1 value too high. A length of 0x100 gives
Keith> ar.lc == r21 == 2. .unaligned_src incorrectly copies r21 into ar.lc,
Keith> when it should copy cnt, so the lfetch lines are executed 3 times, not
Keith> 2. That takes dst_pre_mem past the end of the page and into an
Keith> unallocated area, oops.
That's a good thing to fix (it's definitely a performance bug). However,
lfetch.fault should be safe to use even on unmapped memory. See this
code in ia64_do_page_fault():
/*
* This fault was due to a speculative load or lfetch.fault, set the "ed"
* bit in the psr to ensure forward progress. (Target register will get a
* NaT for ld.s, lfetch will be canceled.)
*/
I don't see off-hand why this wouldn't work as intended.
--david
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