From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:39527)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <avi@redhat.com>) id 1TEGvB-0001VA-6Z
	for qemu-devel@nongnu.org; Wed, 19 Sep 2012 05:50:18 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <avi@redhat.com>) id 1TEGv5-00007P-Dt
	for qemu-devel@nongnu.org; Wed, 19 Sep 2012 05:50:17 -0400
Received: from mx1.redhat.com ([209.132.183.28]:2315)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <avi@redhat.com>) id 1TEGv5-000075-5U
	for qemu-devel@nongnu.org; Wed, 19 Sep 2012 05:50:11 -0400
Message-ID: <5059954A.50408@redhat.com>
Date: Wed, 19 Sep 2012 12:50:02 +0300
From: Avi Kivity <avi@redhat.com>
MIME-Version: 1.0
References: <CAJnKYQmv=k9QhcTfVzXcdqnFxZiCsZTehC8pGWeVCfBq7FX0zg@mail.gmail.com>
	<50597D1F.3070607@redhat.com>
	<CAJnKYQ=yKMNLtsQGu3ABvug+XrVr9DbGnKq3DhWE8koLKWw6Aw@mail.gmail.com>
	<505991A2.6090709@siemens.com>
In-Reply-To: <505991A2.6090709@siemens.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [big lock] Discussion about the convention of
 device's DMA each other after breaking down biglock
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: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, liu ping fan <qemulist@gmail.com>, Anthony Liguori <anthony@codemonkey.ws>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

On 09/19/2012 12:34 PM, Jan Kiszka wrote:
> 
> What about the following:
> 
> What we really need to support in practice is MMIO access triggers RAM
> access of device model. Scenarios where a device access triggers another
> MMIO access could likely just be rejected without causing troubles.
> 
> So, when we dispatch a request to a device, we mark that the current
> thread is in a MMIO dispatch and reject any follow-up c_p_m_rw that does
> _not_ target RAM, ie. is another, nested MMIO request - independent of
> its destination. How much of the known issues would this solve? And what
> would remain open?

Various iommu-like devices re-dispatch I/O, like changing endianness or
bitband.  I don't know whether it targets I/O rather than RAM.

If they do, we can push the support into the memory API.  I think it's
acceptable as a short term solution (short term meaning as long as needed).



-- 
error compiling committee.c: too many arguments to function