From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:33250)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UaMF8-0002G6-Sk
	for qemu-devel@nongnu.org; Thu, 09 May 2013 04:30:27 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UaMF7-0003Td-Qu
	for qemu-devel@nongnu.org; Thu, 09 May 2013 04:30:26 -0400
Received: from mail-wg0-x229.google.com ([2a00:1450:400c:c00::229]:60392)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UaMF7-0003TU-K6
	for qemu-devel@nongnu.org; Thu, 09 May 2013 04:30:25 -0400
Received: by mail-wg0-f41.google.com with SMTP id y10so6004330wgg.4
	for <qemu-devel@nongnu.org>; Thu, 09 May 2013 01:30:25 -0700 (PDT)
Date: Thu, 9 May 2013 10:30:17 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130509083017.GH1074@stefanha-thinkpad.redhat.com>
References: <1368060022-16911-1-git-send-email-qemulist@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1368060022-16911-1-git-send-email-qemulist@gmail.com>
Subject: Re: [Qemu-devel] [PATCH 1/2] Vring: vring's listener's priority
 should higher than kvm
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: Liu Ping Fan <qemulist@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Anthony Liguori <anthony@codemonkey.ws>, "Michael S. Tsirkin" <mst@redhat.com>, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>

On Thu, May 09, 2013 at 08:40:21AM +0800, Liu Ping Fan wrote:
> From: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> 
> Hosts threads which handle vring should have high MemoryListener priority
> than kvm. For currently code, take the following scenario:
>   kvm_region_add() run earlier before vhost_region_add(), then in guest,
> vring's desc[i] can refer to addressX in the new region known by guest.
> But vhost does not know this new region yet, and the vring handler will
> fail.

Is there a concrete scenario where this happens?

I can think of situations like the ioeventfd being readable before
vhost/hostmem is populated.  But I don't see how that's related to the
priority of kvm_region_add().

Stefan