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" ?
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 ?
Thanks,
Mathieu
Andrea
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
