Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 17 Jul 2020 09:42:43 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To:     Nicholas Piggin <npiggin@gmail.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Anton Blanchard <anton@ozlabs.org>,
        Arnd Bergmann <arnd@arndb.de>,
        linux-arch <linux-arch@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>, x86 <x86@kernel.org>
Message-ID: <1314561373.18530.1594993363050.JavaMail.zimbra@efficios.com>
In-Reply-To: <1594906688.ikv6r4gznx.astroid@bobo.none>
References: <1594868476.6k5kvx8684.astroid@bobo.none> <EFAD6E2F-EC08-4EB3-9ECC-2A963C023FC5@amacapital.net> <20200716085032.GO10769@hirez.programming.kicks-ass.net> <1594892300.mxnq3b9a77.astroid@bobo.none> <20200716110038.GA119549@hirez.programming.kicks-ass.net> <1594906688.ikv6r4gznx.astroid@bobo.none>
Subject: Re: [RFC PATCH 4/7] x86: use exit_lazy_tlb rather than
 membarrier_mm_sync_core_before_usermode
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Thread-Topic: x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before_usermode
Thread-Index: tih2wG5S7/k8ds/ZwlGdEfhVUfBRJg==
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

----- 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