On Wed, Jan 24, 2024 at 01:56:39PM -0500, Mathieu Desnoyers wrote: > On 2024-01-24 13:44, Andrea Parri wrote: > > > > +# riscv uses xRET as return from interrupt and to return to user-space. > > > > +# > > > > +# Given that xRET is not core serializing, we rely on FENCE.I for providing > > > > +# core serialization: > > > > +# > > > > +# - by calling sync_core_before_usermode() on return from interrupt (cf. > > > > +# ipi_sync_core()), > > > > +# > > > > +# - via switch_mm() and sync_core_before_usermode() (respectively, for > > > > +# uthread->uthread and kthread->uthread transitions) to go back to > > > > +# user-space. > > > > > > I don't quite get the meaning of the sentence above. There seems to be a > > > missing marker before "to go back". > > > > Let's see. Without the round brackets, the last part becomes: > > > > - via switch_mm() and sync_core_before_usermode() to go back to > > user-space. > > > > This is indeed what I meant to say. What am I missing? > > Would it still fit your intent if we say "before returning to > user-space" rather than "to go back to user-space" ? Yes, works for me. Will change in v4. > Because the switch_mm(), for instance, does not happen exactly on > return to user-space, but rather when the scheduler switches tasks. > Therefore, I think that stating that core serialization needs to > happen before returning to user-space is clearer than stating that > it happens "when" we go back to user-space. > > Also, on another topic, did you find a way forward with respect of > the different choice of words between the membarrier man page and > documentation vs the RISC-V official semantic with respect to "core > serializing" vs FENCE.I ? The way forward I envision involves the continuous (iterative) discussion /review of the respective documentation and use-cases/litmus tests/models /etc. AFAICS, that is not that different from discussions about smp_mb() (as in memory-barriers.txt) vs. FENCE RW,RW (RISC-V ISA manual) - only time will tell. Andrea
