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Date:   Wed, 15 Jan 2020 14:12:24 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Arnd Bergmann <arnd@arndb.de>
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>
Subject: Re: [RFC 1/4] asm-generic/uaccess: don't define inline functions if
 noinline lib/* in use
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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.