Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs

On Tue, Jul 03, 2018 at 11:17:17AM +0200, Heiko Carstens wrote:

And to answer also your question: we don't use a regular load, since we
would have to use 'sacf' construct surrounding the load instruction which
would be much slower.
We have something like that implemented for the futex atomic ops, and we
could also implement something like that for this use case
(e.g. get_user_atomic()), if really needed.

/me digs out the s390-PoO PDF and understands.. this is because of the
split user/kernel address space stuff.

Fair enough.