From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:37186)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1SF0c3-0005at-52
	for qemu-devel@nongnu.org; Tue, 03 Apr 2012 06:05:23 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1SF0bw-0000S4-6y
	for qemu-devel@nongnu.org; Tue, 03 Apr 2012 06:05:18 -0400
Received: from mx1.redhat.com ([209.132.183.28]:61417)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1SF0bv-0000Rt-UY
	for qemu-devel@nongnu.org; Tue, 03 Apr 2012 06:05:12 -0400
Date: Tue, 3 Apr 2012 13:05:15 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20120403100515.GA9697@redhat.com>
References: <1333393194.3799.175.camel@bling.home>
	<f98fb4eb-fc31-42e6-b066-bd3d6b67af4a@zmail16.collab.prod.int.phx2.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <f98fb4eb-fc31-42e6-b066-bd3d6b67af4a@zmail16.collab.prod.int.phx2.redhat.com>
Subject: Re: [Qemu-devel] [PATCHv3] piix: fix up/down races
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: Igor Mammedov <imammedo@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, gleb@redhat.com, qemu-devel@nongnu.org, Isaku Yamahata <yamahata@valinux.co.jp>, Alex Williamson <alex.williamson@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Aurelien Jarno <aurelien@aurel32.net>

On Tue, Apr 03, 2012 at 02:40:41AM -0400, Igor Mammedov wrote:
> > > +     */
> > > +    s->pci0_status.down &= ~(1U << slot);
> > 
> > Should we clear "up" here too?
> Is it possible to create pci dev for not yet freed pci slot?

It's not possible ATM.

> If not then we should not care, otherwise we should fix that.
> > > @@ -567,8 +595,6 @@ static int piix4_device_hotplug(DeviceState
> > > *qdev, PCIDevice *dev,
> > >          return 0;
> > >      }
> > >  
> > > -    s->pci0_status.up = 0;
> > > -    s->pci0_status.down = 0;
> > >      if (state == PCI_HOTPLUG_ENABLED) {
> > >          enable_device(s, slot);
> > >      } else {
> > 
> > So if we have an old bios and do an add, followed by a remove, guest
> > ACPI finds both "up" and "down" set for the slot and we rely on the
> > ordering of the AML checking up before down to keep the duct tape and
> > bailing wire from exploding?

In fact UP triggers a rescan - there is no injection event in ACPI.
So it seems you can check the events in any order.

> >  Hmm, can't say I'm excited about this
> > hack
> > either.  Thanks,
> > 
> > Alex
> > 
> >