From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=55266 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1OY4YT-0005nL-Ky
	for qemu-devel@nongnu.org; Sun, 11 Jul 2010 17:59:22 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <alex.williamson@redhat.com>) id 1OY4YS-0005xi-Ds
	for qemu-devel@nongnu.org; Sun, 11 Jul 2010 17:59:21 -0400
Received: from mx1.redhat.com ([209.132.183.28]:59114)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <alex.williamson@redhat.com>) id 1OY4YS-0005xa-5X
	for qemu-devel@nongnu.org; Sun, 11 Jul 2010 17:59:20 -0400
From: Alex Williamson <alex.williamson@redhat.com>
In-Reply-To: <20100711201246.GA12544@redhat.com>
References: <20100711180910.20121.93313.stgit@localhost6.localdomain6>
	<20100711180936.20121.35376.stgit@localhost6.localdomain6>
	<4C3A09F3.8010304@redhat.com> <1278872784.20397.18.camel@x201>
	<4C3A0DE3.8010806@redhat.com> <20100711185456.GA11048@redhat.com>
	<1278876078.20397.79.camel@x201> <20100711192330.GA11491@redhat.com>
	<1278878614.20397.128.camel@x201> <20100711201246.GA12544@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Date: Sun, 11 Jul 2010 15:59:15 -0600
Message-ID: <1278885555.20397.181.camel@x201>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Subject: [Qemu-devel] Re: [RFC PATCH 4/5] APIC/IOAPIC EOI callback
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.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: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: chrisw@redhat.com, pugs@cisco.com, Avi Kivity <avi@redhat.com>, kvm@vger.kernel.org, qemu-devel@nongnu.org

On Sun, 2010-07-11 at 23:12 +0300, Michael S. Tsirkin wrote:
> On Sun, Jul 11, 2010 at 02:03:34PM -0600, Alex Williamson wrote:
> > > What about threaded interrupts?
> 
> Just to make the point, imagine a nested virt situation
> which uses current kvm device assignment in guest.
> Look at the interrupt handler we have there.

Is the problem you're worried about this:

	guest masks qemu ioapic rte
	device interrupt
	host vfio DisINTx+
	qemu vfio calls qemu_set_irq
	...

In that case, the qemu ioapic irr bit is only toggled by qemu_set_irq
for level triggered interrupts, so the interrupt will be asserted in the
guest when it gets unmasked and we'll get the eoi.

I can't figure out where your other scenario can leave the DisINTx+:

	device asserts interrupt
	a) DisINTx+ via host vfio
	guest disables interrupt
	b) DisINTx+ via guest, already set
	eoi
	c) DisINTx- via qemu vfio
	driver clears interrupt        
	guest enables interrupt
	d) DisINTx- via guest
	device asserts interrupt

So between c) & d) we're potentially getting more interrupts than we
want, but I can't see anywhere that we drop DisINTx.  If you have a
scenario, let me know.  Thanks,

Alex