From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1MEOT1-0004PG-LS
	for qemu-devel@nongnu.org; Wed, 10 Jun 2009 10:07:51 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1MEOSv-0004Md-Ra
	for qemu-devel@nongnu.org; Wed, 10 Jun 2009 10:07:50 -0400
Received: from [199.232.76.173] (port=44628 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1MEOSv-0004MX-LX
	for qemu-devel@nongnu.org; Wed, 10 Jun 2009 10:07:45 -0400
Received: from mx20.gnu.org ([199.232.41.8]:57208)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <paul@codesourcery.com>)
	id 1MEOSv-00024t-9L
	for qemu-devel@nongnu.org; Wed, 10 Jun 2009 10:07:45 -0400
Received: from mail.codesourcery.com ([65.74.133.4])
	by mx20.gnu.org with esmtp (Exim 4.60)
	(envelope-from <paul@codesourcery.com>) id 1MEOSt-000118-Bh
	for qemu-devel@nongnu.org; Wed, 10 Jun 2009 10:07:43 -0400
From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions
Date: Wed, 10 Jun 2009 15:07:34 +0100
References: <cover.1243253205.git.mst@redhat.com>
	<200906100019.59981.paul@codesourcery.com>
	<20090610094604.GD6844@redhat.com>
In-Reply-To: <20090610094604.GD6844@redhat.com>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200906101507.39823.paul@codesourcery.com>
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Carsten Otte <cotte@de.ibm.com>, kvm@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, Blue Swirl <blauwirbel@gmail.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Avi Kivity <avi@redhat.com>

> > > Note that platform must set a flag to declare MSI supported.
> > > For PC this will be set by APIC.
> >
> > This sounds wrong. The device shouldn't know or care whether the system
> > has a MSI capable interrupt controller. That's for the guest OS to figure
> > out.
>
> You are right of course. In theory there's nothing that breaks if I
> set this flag to on, on all platforms. OTOH if qemu emulates some
> controller incorrectly, guest might misdetect MSI support in the
> controller, and things will break horribly.
>
> It seems safer to have a flag that can be enabled by people
> that know about a specific platform.

No. The solution is to fix whatever is broken.

If we really need to avoid MSI-X capable devices then that should be done 
explicity per-device. i.e. you have a different virtio-net device that does 
not use MSI-X.

Paul