linux-kernel - Re: [PATCH v3 2/7] uaccess: Tell user_access

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Date:   Thu, 23 Jan 2020 15:11:05 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        dri-devel@...ts.freedesktop.org, x86@...nel.org
Subject: Re: [PATCH v3 2/7] uaccess: Tell user_access_begin() if it's for a write or not

On Thu, 23 Jan 2020, Christophe Leroy <christophe.leroy@....fr> wrote:
> On 32 bits powerPC (book3s/32), only write accesses to user are
> protected and there is no point spending time on unlocking for reads.
>
> On 64 bits powerpc (book3s/64 at least), access can be granted
> read only, write only or read/write.
>
> Add an argument to user_access_begin() to tell when it's for write and
> return an opaque key that will be used by user_access_end() to know
> what was done by user_access_begin().

IMHO an opaque key is a prime example of a case where the use of an
opaque typedef is warranted. Nobody needs to know or care it's
specifically an unsigned long.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center