On Wed, Aug 17, 2016 at 2:35 PM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Wed, Aug 17, 2016 at 2:26 PM, Linus Torvalds > <torva...@linux-foundation.org> wrote: >> >> Of course, if somebody uses native_restore_fl() to actually *disable* >> interrupts (when they weren't already disabled), then this untested >> patch will just not work. But why would you do somethign so stupid? >> Famous last words... > > Looking around, the vsmp code actually uses "native_restore_fl()" to > not just set the interrupt flag, but AC as well. > > And the PV spinlock case has that "push;popf" sequence encoded in an > alternate. > > So that trivial patch may (or may not - still not tested) work for > some quick testing, but needs more effort for any *real* use. >
It shouldn't be *too* bad, since xen_restore_fl only affects "IF". And even if native_restore_fl needs to be able to turn IRQs off as well as on, we can just do: if (likely(flags & X86_EFLAGS_IF)) sti(); else cli(); at some cost to code size but hopefully little to no runtime cost for the sane cases.
