Re: [RFC PATCH 4/7] x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before_usermode

----- On Jul 16, 2020, at 7:26 PM, Nicholas Piggin npiggin@gmail.com wrote:
[...]

membarrier does replace barrier instructions on remote CPUs, which do
order accesses performed by the kernel on the user address space. So
membarrier should too I guess.

Normal process context accesses like read(2) will do so because they
don't get filtered out from IPIs, but kernel threads using the mm may
not.

But it should not be an issue, because membarrier's ordering is only with respect
to submit and completion of io_uring requests, which are performed through
system calls from the context of user-space threads, which are called from the
right mm.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com