linux-kernel - Re: [PATCH 6/7] powerpc/uaccess: Add unsafe_clear

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Message-ID: <1940d0cc-1aea-07d0-95e6-8d63047e4d9e@csgroup.eu>
Date:   Tue, 15 Jun 2021 09:10:53 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] powerpc/uaccess: Add unsafe_clear_user()

Le 15/06/2021 à 08:53, Christoph Hellwig a écrit :
> On Tue, Jun 15, 2021 at 06:41:02AM +0000, Christophe Leroy wrote:
>> Implement unsafe_clear_user() for powerpc.
>> It's a copy/paste of unsafe_copy_to_user() with value 0 as source.
>>
>> It may be improved in a later patch by using 'dcbz' instruction
>> to zeroize full cache lines at once.
> 
> Please add this to common code insted of making it powerpc specific.
> 

A common version is added in previous patch.

Just like unsafe_copy_to_user(), unsafe_clear_user() needs to be arch defined.

unsafe_copy_to_user() has both an x86 implementation and a powerpc implementation, why do different ?

I can't see how it could be not powerpc specific. At the end we want to use 'dcbz' to zeroize full 
cachelines at once, even if at the time being that's a simple write of 0.