From: Jan Kara
Sent: 17 May 2019 09:48
So this last paragraph is not obvious to me as check_copy_size() does
of various checks in CONFIG_HARDENED_USERCOPY case. I agree that some of
those checks don't make sense for PMEM pages but I'd rather handle that by
refining check_copy_size() and check_object_size() functions to detect and
appropriately handle pmem pages rather that generally skip all the checks
in pmem_copy_from/to_iter(). And yes, every check in such hot path is going
to cost performance but that's what user asked for with
Except that all the distros enable it by default.
So you get the performance cost whether you (as a user) want it or not.
I've changed some of our code to use __get_user() to avoid
these stupid overheads.
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