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Subject: Re: [PATCH 8/8] membarrier: Rewrite sync_core_before_usermode() and
 improve documentation
To:     Nicholas Piggin <npiggin@gmail.com>, x86@kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@intel.com>,
        linux-arm-kernel@lists.infradead.org,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        linuxppc-dev@lists.ozlabs.org,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Paul Mackerras <paulus@samba.org>,
        Peter Zijlstra <peterz@infradead.org>, stable@vger.kernel.org,
        Will Deacon <will@kernel.org>
References: <cover.1623813516.git.luto@kernel.org>
 <07a8b963002cb955b7516e61bad19514a3acaa82.1623813516.git.luto@kernel.org>
 <1623818343.eko1v01gvr.astroid@bobo.none>
From:   Andy Lutomirski <luto@kernel.org>
Message-ID: <1e248763-9372-6e4e-5dea-cda999000aeb@kernel.org>
Date:   Wed, 16 Jun 2021 11:52:58 -0700
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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!