Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754717AbcJEVhj (ORCPT <rfc822;w@1wt.eu>);
        Wed, 5 Oct 2016 17:37:39 -0400
Received: from mail-oi0-f66.google.com ([209.85.218.66]:34434 "EHLO
        mail-oi0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751020AbcJEVhh (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 5 Oct 2016 17:37:37 -0400
MIME-Version: 1.0
In-Reply-To: <20161005204452.GB26721@remoulade>
References: <1475589000-29315-1-git-send-email-fredrik.markstrom@gmail.com>
 <1475595363-4272-1-git-send-email-fredrik.markstrom@gmail.com>
 <20161004170741.GC29008@leverpostej> <CAKdL+dS4_My6hyMEGNc65mzDapia_tMiVzZ9DMw=ddZM+XiwAw@mail.gmail.com>
 <CAKdL+dTGDqgpnMTkAj=N4cY-cZF_U+bkH1v1vUA4umZoSbWHKQ@mail.gmail.com>
 <50e025e0-7052-9b15-3b3e-36d1d9dfd695@arm.com> <CAKdL+dQH=9C2aGf7ys5-vXM7pkdPYUQ8xYWLipwVbABOz09f1g@mail.gmail.com>
 <20161005204452.GB26721@remoulade>
From: =?UTF-8?Q?Fredrik_Markstr=C3=B6m?= <fredrik.markstrom@gmail.com>
Date: Wed, 5 Oct 2016 23:37:06 +0200
Message-ID: <CAKdL+dTYR7Ch9uwyzZGG_wz533pth_+4CkAzYtzaCVn5bF20ig@mail.gmail.com>
Subject: Re: [PATCH v2] arm: Added support for getcpu() vDSO using TPIDRURW
To: Mark Rutland <mark.rutland@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>, Kees Cook <keescook@chromium.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Nicolas Pitre <nico@linaro.org>, Will Deacon <will.deacon@arm.com>,
        Russell King <linux@armlinux.org.uk>, kristina.martsenko@arm.com,
        linux-kernel@vger.kernel.org,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Chris Brandt <chris.brandt@renesas.com>,
        Michal Marek <mmarek@suse.com>, Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>,
        linux-arm-kernel@lists.infradead.org,
        Jonathan Austin <jonathan.austin@arm.com>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id u95Lbhbp014616
Content-Length: 1007
Lines: 29

On Wed, Oct 5, 2016 at 10:44 PM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Wed, Oct 05, 2016 at 08:00:38PM +0000, Fredrik Markström wrote:
>> On Wed, Oct 5, 2016 at 7:48 PM Robin Murphy <robin.murphy@arm.com> wrote:
>> As far as I understand TPIDRURW isn't anything else then an architecture
>> specific piece of tls since the last patch, possibly slightly faster then a
>> "__thread u32 x;"
>>
>> The irony is that the two different ways it was handled earlier (not context
>> switched or always set to zero on swap in) would have made it useful for this
>> purpose.
>
> The "not context switched" case was also arbitrarily corrupted, and could not
> have been relied upon.

Ok, I missed that, sorry !

>
> The zeroing case is similar to the restartable sequences design. So that's
> probably worth looking into.

Ok, I'm starting to believe my best bet is to hope that those make it
into the kernel
eventually, until then I'll probably just go with a local solution.

/Fredrik

>
> Thanks,
> Mark.