RE: [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED_USERCOPY overhead

[David Laight]

From: Jan Kara
> Sent: 17 May 2019 09:48
...
> So this last paragraph is not obvious to me as check_copy_size() does a lot
> 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
> CONFIG_HARDENED_USERCOPY... Kees?

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.

	David

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