On 2/17/2015 5:54 AM, Sebastian Andrzej Siewior wrote:
* 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 :)
Yes, it works. I found it on mips64 target.
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 :)
Yes, the highpage is just used for dealing with MIPS dcache alias issue. I'm going to rebase it onto 3.18. Thanks, Yang
Sebastian
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