From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:44658)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1bjs1H-0003Rs-NN
	for qemu-devel@nongnu.org; Tue, 13 Sep 2016 14:01:20 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1bjs1D-0001JS-Ka
	for qemu-devel@nongnu.org; Tue, 13 Sep 2016 14:01:19 -0400
Received: from mail-yw0-f181.google.com ([209.85.161.181]:36407)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1bjs1D-0001Il-Ev
	for qemu-devel@nongnu.org; Tue, 13 Sep 2016 14:01:15 -0400
Received: by mail-yw0-f181.google.com with SMTP id u124so97285215ywg.3
	for <qemu-devel@nongnu.org>; Tue, 13 Sep 2016 11:01:15 -0700 (PDT)
Sender: Richard Henderson <rth7680@gmail.com>
References: <1472935202-3342-1-git-send-email-rth@twiddle.net>
	<1472935202-3342-14-git-send-email-rth@twiddle.net>
	<87vay1w7p8.fsf@linaro.org>
From: Richard Henderson <rth@twiddle.net>
Message-ID: <f851ddba-bc62-2477-dd05-3f7e9d364668@twiddle.net>
Date: Tue, 13 Sep 2016 11:00:11 -0700
MIME-Version: 1.0
In-Reply-To: <87vay1w7p8.fsf@linaro.org>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Subject: Re: [Qemu-devel] [PATCH v3 13/34] tcg: Add atomic helpers
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>
Cc: qemu-devel@nongnu.org

On 09/12/2016 06:47 AM, Alex Bennée wrote:
>> > +    /* Notice an IO access, or a notdirty page.  */
>> > +    if (unlikely(tlb_addr & ~TARGET_PAGE_MASK)) {
>> > +        /* There's really nothing that can be done to
>> > +           support this apart from stop-the-world.  */
>> > +        goto stop_the_world;
> We are also triggering on TLB_NOTDIRTY here in the case where a
> conditional write is the first write to a page. I don't know if a
> stop_the_world is required at this point but we will need to ensure we
> clear bits as notdirty_mem_write() does.
> 

You're quite right that we could probably special-case TLB_NOTDIRTY here such
that (1) we needn't leave the cpu loop, and (2) needn't utilize the actual
"write" part of notdirty_mem_write; just set the bits then fall through to the
actual atomic instruction below.


r~