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

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Message-ID: <1e248763-9372-6e4e-5dea-cda999000aeb@kernel.org>
Date:   Wed, 16 Jun 2021 11:52:58 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Nicholas Piggin <npiggin@...il.com>, 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,
        LKML <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 <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 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


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

Thanks!