From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:44610)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <alex.bennee@linaro.org>) id 1YLO2w-0007BW-00
	for qemu-devel@nongnu.org; Tue, 10 Feb 2015 22:33:02 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <alex.bennee@linaro.org>) id 1YLO2s-000667-RH
	for qemu-devel@nongnu.org; Tue, 10 Feb 2015 22:33:01 -0500
Received: from static.88-198-71-155.clients.your-server.de
	([88.198.71.155]:60698 helo=socrates.bennee.com)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <alex.bennee@linaro.org>) id 1YLO2s-00065x-Lg
	for qemu-devel@nongnu.org; Tue, 10 Feb 2015 22:32:58 -0500
References: <54D885A0.3080609@greensocs.com>
From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
In-reply-to: <54D885A0.3080609@greensocs.com>
Date: Wed, 11 Feb 2015 03:33:22 +0000
Message-ID: <87pp9hrukd.fsf@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Subject: Re: [Qemu-devel] CPU TLB flush with multithread TCG.
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: Frederic Konrad <fred.konrad@greensocs.com>
Cc: mttcg@listserver.greensocs.com, Peter Maydell <peter.maydell@linaro.org>, Jan Kiszka <jan.kiszka@siemens.com>, Alexander Graf <agraf@suse.de>, qemu-devel <qemu-devel@nongnu.org>, Paolo Bonzini <pbonzini@redhat.com>


Frederic Konrad <fred.konrad@greensocs.com> writes:

> Hi everybody,
>
> In multithread tlb_flush is broken as CPUA can flush an other CPUB and 
> CPUB can be
> executing code, and fixing this can be quite hard:
>    * We need to exit the CPU which is flushed.
>    * Makes sure the CPU is stopped.
>    * Then we can flush tlb.
> The big issues are:
>    * Two threads can be doing a flush at the same time.
>    * Something can restart the CPU during the flush.
>
> A better idea I think is that instead of flushing tlb we can put a flag 
> in CPUState such
> as flush_request and ask the cpu to exit.
> Then later once the CPU is exited we can flush tlbs if flush_request is set.
> It will ensure that the CPU won't execute code as it's associated thread 
> will be
> flushing.
>
> Can this work?

Does this imply deferring the work? Surely if we don't flush when
instructed things could break down very quickly?



>
> Thanks,
> Fred

-- 
Alex Bennée