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

From: Mathieu Desnoyers <[email-masked]>
Date: Fri, 17 Jul 2020 09:42:43 -0400 (EDT)

----- On Jul 16, 2020, at 7:26 PM, Nicholas Piggin [email-masked] 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