On Sat, Nov 28, 2020 at 8:02 AM Nicholas Piggin <npiggin@xxxxxxxxx> wrote: > > And get rid of the generic sync_core_before_usermode facility. This is > functionally a no-op in the core scheduler code, but it also catches > > This helper is the wrong way around I think. The idea that membarrier > state requires a core sync before returning to user is the easy one > that does not need hiding behind membarrier calls. The gap in core > synchronization due to x86's sysret/sysexit and lazy tlb mode, is the > tricky detail that is better put in x86 lazy tlb code. > > Consider if an arch did not synchronize core in switch_mm either, then > membarrier_mm_sync_core_before_usermode would be in the wrong place > but arch specific mmu context functions would still be the right place. > There is also a exit_lazy_tlb case that is not covered by this call, which > could be a bugs (kthread use mm the membarrier process's mm then context > switch back to the process without switching mm or lazy mm switch). > > This makes lazy tlb code a bit more modular. I have a couple of membarrier fixes that I want to send out today or tomorrow, and they might eliminate the need for this patch. Let me think about this a little bit. I'll cc you. The existing code is way to subtle and the comments are far too confusing for me to be quickly confident about any of my conclusions :)
