linux-kernel - Re: [PATCH 2/8] x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before

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Message-ID: <274632921.67676.1606748272576.JavaMail.zimbra@efficios.com>
Date:   Mon, 30 Nov 2020 09:57:52 -0500 (EST)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-mm <linux-mm@...ck.org>, Anton Blanchard <anton@...abs.org>
Subject: Re: [PATCH 2/8] x86: use exit_lazy_tlb rather than
 membarrier_mm_sync_core_before_usermode

----- On Nov 28, 2020, at 11:01 AM, Nicholas Piggin npiggin@...il.com wrote:

> And get rid of the generic sync_core_before_usermode facility. This is
> functionally a no-op in the core scheduler code, but it also catches

This sentence is incomplete.

> 
> This helper is the wrong way around I think. The idea that membarrier
> state requires a core sync before returning to user is the easy one
> that does not need hiding behind membarrier calls. The gap in core
> synchronization due to x86's sysret/sysexit and lazy tlb mode, is the
> tricky detail that is better put in x86 lazy tlb code.

Ideally yes this complexity should sit within the x86 architecture code
if only that architecture requires it.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com