linux-kernel - Re: [PATCH 8/8] membarrier: Rewrite sync_core_before

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Date:   Wed, 16 Jun 2021 16:48:54 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Nicholas Piggin" <npiggin@...il.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Cc:     "Andrew Morton" <akpm@...ux-foundation.org>,
        "Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Dave Hansen" <dave.hansen@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        "Paul Mackerras" <paulus@...ba.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        stable@...r.kernel.org, "Will Deacon" <will@...nel.org>
Subject: Re: [PATCH 8/8] membarrier: Rewrite sync_core_before_usermode() and improve documentation

On Wed, Jun 16, 2021, at 11:52 AM, Andy Lutomirski wrote:
> On 6/15/21 9:45 PM, Nicholas Piggin wrote:
> > Excerpts from Andy Lutomirski's message of June 16, 2021 1:21 pm:
> >> The old sync_core_before_usermode() comments suggested that a non-icache-syncing
> >> return-to-usermode instruction is x86-specific and that all other
> >> architectures automatically notice cross-modified code on return to
> >> userspace.
> 
> >> +/*
> >> + * XXX: can a powerpc person put an appropriate comment here?
> >> + */
> >> +static inline void membarrier_sync_core_before_usermode(void)
> >> +{
> >> +}
> >> +
> >> +#endif /* _ASM_POWERPC_SYNC_CORE_H */
> > 
> > powerpc's can just go in asm/membarrier.h
> 
> $ ls arch/powerpc/include/asm/membarrier.h
> ls: cannot access 'arch/powerpc/include/asm/membarrier.h': No such file
> or directory

Which is because I deleted it.  Duh.  I'll clean this up.

> 
> 
> > 
> > /*
> >  * The RFI family of instructions are context synchronising, and
> >  * that is how we return to userspace, so nothing is required here.
> >  */
> 
> Thanks!
>