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

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Message-ID: <d1f62354-5249-f258-1a31-d3e8aebc29d7@csgroup.eu>
Date:   Fri, 18 Jun 2021 17:27:21 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Andy Lutomirski <luto@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>, x86@...nel.org
Cc:     Will Deacon <will@...nel.org>, linux-mm@...ck.org,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        Dave Hansen <dave.hansen@...el.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Paul Mackerras <paulus@...ba.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 8/8] membarrier: Rewrite sync_core_before_usermode() and
 improve documentation



Le 16/06/2021 à 20:52, Andy Lutomirski a écrit :
> 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

https://github.com/torvalds/linux/blob/master/arch/powerpc/include/asm/membarrier.h


Was added by https://github.com/torvalds/linux/commit/3ccfebedd8cf54e291c809c838d8ad5cc00f5688

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