* Yang Shi | 2014-11-06 15:45:27 [-0800]:
>In k{un}map_coherent, pagefault_disable and pagefault_enable are called
>respectively, but k{un}map_coherent needs preempt disabled according to
>commit f8829caee311207afbc882794bdc5aa0db5caf33 ("[MIPS] Fix aliasing bug
>in copy_to_user_page / copy_from_user_page") to avoid dcache alias on COW.
>
>k{un}map_coherent are just called when cpu_has_dc_aliases == 1 with VIPT cache.
>However, actually, the most modern MIPS processors have PIPT dcache without
>dcache alias issue. In such case, k{un}map_atomic will be called with preempt
>enabled.
>
>To fix this, we replace pagefault_* to raw version in k{un}map_coherent, which
>disables preempt, otherwise the following kernel panic may be caught:
And this works? One thing that confuses me is that you talk about kmap()
while there is no HIGHMEM support in MIPS. The other thing is that I had
a longson a while ago and I don't remember this. But it could have no
dcache alias problem :)
Your registers look 64bit wide so this highpage thingy is probably
just to deal with the dcache alias. So if this is the only problem you
have I would be happy to take your patch. Could you please rebase it
against v3.18? The code changed slightly and I would not want to touch
and break it :)
Sebastian
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