The main __copy_user loop looks like this:
2:
EX(.failure_in3,(p16) ld8 val1[0]=[src1],16)
(p16) ld8 val2[0]=[src2],16
EX(.failure_out, (EPI) st8 [dst1]=val1[PIPE_DEPTH-1],16)
(EPI) st8 [dst2]=val2[PIPE_DEPTH-1],16
br.ctop.dptk 2b
What I'm trying to understand is why there is no EX necessary on the
second store. As far as I understand the implementation, src is 16-byte
aligned here, so there is no need for EX on the second load, since it
necessarily hits the same page. But dst is only 8-byte aligned, so I
would think that the second store could fault.
I've done some testing and for some reason it doesn't seem to be a
problem in Linux; I haven't been able to produce an oops. But I've hit
oopses in Xen (we use the same code), and so I'm trying to understand
*why* it's not a problem in Linux.
Does anyone have some insight?
Matt
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