linux-kernel - Re: [RFC PATCH 4/7] x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before

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Date:   Mon, 13 Jul 2020 23:47:14 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Anton Blanchard <anton@...abs.org>, Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>
Subject: Re: [RFC PATCH 4/7] x86: use exit_lazy_tlb rather than
 membarrier_mm_sync_core_before_usermode

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.

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