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Date: Mon, 13 Jul 2020 10:13:21 -0400 (EDT) From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> To: Nicholas Piggin <npiggin@...il.com> Cc: Andy Lutomirski <luto@...nel.org>, Anton Blanchard <anton@...abs.org>, Arnd Bergmann <arnd@...db.de>, linux-arch <linux-arch@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, Peter Zijlstra <peterz@...radead.org>, x86 <x86@...nel.org> Subject: Re: [RFC PATCH 4/7] x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before_usermode ----- On Jul 13, 2020, at 9:47 AM, Nicholas Piggin npiggin@...il.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
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