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Mon, 13 Jul 2020 10:13:21 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id 91AC42A2095; Mon, 13 Jul 2020 10:13:21 -0400 (EDT) Date: Mon, 13 Jul 2020 10:13:21 -0400 (EDT) From: Mathieu Desnoyers To: Nicholas Piggin Cc: Andy Lutomirski , Anton Blanchard , Arnd Bergmann , linux-arch , linux-kernel , linux-mm , linuxppc-dev , Peter Zijlstra , x86 Message-ID: <284592761.9860.1594649601492.JavaMail.zimbra@efficios.com> In-Reply-To: <1594647408.wmrazhwjzb.astroid@bobo.none> References: <20200710015646.2020871-1-npiggin@gmail.com> <20200710015646.2020871-5-npiggin@gmail.com> <1594613902.1wzayj0p15.astroid@bobo.none> <1594647408.wmrazhwjzb.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 X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_3955 (ZimbraWebClient - FF78 (Linux)/8.8.15_GA_3953) Thread-Topic: x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before_usermode Thread-Index: T7nLE24o9VdoF/eNvu+hhgTHKlctBA== X-Rspamd-Queue-Id: 36C7A180F76D8 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: ----- On Jul 13, 2020, at 9:47 AM, Nicholas Piggin npiggin@gmail.com wrote: > Excerpts from Nicholas Piggin's message of July 13, 2020 2:45 pm: >> Excerpts from Andy Lutomirski's message of July 11, 2020 3:04 am: >>> Also, as it stands, I can easily see in_irq() ceasing to promise to >>> serialize. There are older kernels for which it does not promise to >>> serialize. And I have plans to make it stop serializing in the >>> nearish future. >> >> You mean x86's return from interrupt? Sounds fun... you'll konw where to >> update the membarrier sync code, at least :) > > Oh, I should actually say Mathieu recently clarified a return from > interrupt doesn't fundamentally need to serialize in order to support > membarrier sync core. Clarification to your statement: Return from interrupt to kernel code does not need to be context serializing as long as kernel serializes before returning to user-space. However, return from interrupt to user-space needs to be context serializing. Thanks, Mathieu > > https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-July/214171.html > > So you may not need to do anything more if you relaxed it. > > Thanks, > Nick -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com