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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 15 Jan 2020 15:21:52 +0100
Message-ID: <CAK8P3a0eu-2ov-Y0EEuv_XSGUTWoyiScf5z5P=kn5S+ORhxF-A@mail.gmail.com>
Subject: Re: [RFC 1/4] asm-generic/uaccess: don't define inline functions if
 noinline lib/* in use
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Vineet Gupta <Vineet.Gupta1@synopsys.com>,
        Khalid Aziz <khalid.aziz@oracle.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Kees Cook <keescook@chromium.org>,
        Ingo Molnar <mingo@kernel.org>,
        Aleksa Sarai <cyphar@cyphar.com>,
        "open list:SYNOPSYS ARC ARCHITECTURE" 
        <linux-snps-arc@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>
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On Wed, Jan 15, 2020 at 3:12 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Wed, Jan 15, 2020 at 10:08:31AM +0100, Arnd Bergmann wrote:
>
> > > I would suggest that anybody who uses asm-generic/uaccess.h needs to
> > > simply use the generic library version.
> >
> > Or possibly just everybody altogether: the remaining architectures that
> > have a custom implementation don't seem to be doing any better either.
>
> No go for s390.  There you really want to access userland memory in
> larger chunks - it's oriented for block transfers.  IIRC, the insn
> they are using has a costly setup phase, independent of the amount
> to copy, followed by reasonably fast transfer more or less linear
> by the size.

Right, I missed that one while looking through the remaining
implementations.

     Arnd