On Tue, Jul 03, 2018 at 09:40:48AM -0700, Andi Kleen wrote: > > > > So I think you're good... But yes, you raise an interresting point. > > So it sounds like architectures that don't have an instruction atomic u64 > *_user need to disable interrupts during the access, and somehow handle that > case when a page fault happens?
So for 32bit, as Linus already said, a split store is _fine_, because the top word is always going to be 0 anyway. So all we really need is native word sized loads / stores. s390 is just a little weird here (it wouldn't be s390 if it wasn't I suppose) for not actually using regular loads / stores because of the split address space stuff.
