From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53916) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a4qXY-0000Ag-1h for qemu-devel@nongnu.org; Fri, 04 Dec 2015 08:36:48 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a4qXX-0003Rq-3X for qemu-devel@nongnu.org; Fri, 04 Dec 2015 08:36:47 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55232) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a4qXW-0003Rd-Ux for qemu-devel@nongnu.org; Fri, 04 Dec 2015 08:36:47 -0500 Date: Fri, 4 Dec 2015 15:36:43 +0200 From: "Michael S. Tsirkin" Message-ID: <20151204153550-mutt-send-email-mst@redhat.com> References: <20151201111108.6dd85381.cornelia.huck@de.ibm.com> <20151201131040.046ab170.cornelia.huck@de.ibm.com> <20151201152153.1bb1f58f.cornelia.huck@de.ibm.com> <565E8781.5060700@redhat.com> <20151202111128.03f4f46d.cornelia.huck@de.ibm.com> <5660F542.8010309@redhat.com> <20151204111548.155ea5f7.cornelia.huck@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151204111548.155ea5f7.cornelia.huck@de.ibm.com> Subject: Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cornelia Huck Cc: Christian Borntraeger , Jason Wang , qemu-devel@nongnu.org On Fri, Dec 04, 2015 at 11:15:48AM +0100, Cornelia Huck wrote: > On Fri, 4 Dec 2015 10:06:58 +0800 > Jason Wang wrote: > > > The problem is for pci: without this patch, guest may always see modern > > bar is "disable-modern=false". But with this patch, on an old kernel > > that does not support VERSION_1, even "disable-modern=false" were > > specified, guest can not see modern bar anymore. Looks like a guest > > visible change. > > But the guest even see a modern bar if the host is not able to present > a spec-compliant device? > > What we have now is a device that looks like a modern device but that > does not offer VERSION_1. Probably not spec compliant. If virtio-pci is > fixed to not present such broken devices to the guest, this is > guest-visible, yes; but only in the sense that the guest will no longer > see broken devices, but simply legacy devices if configured. I agree - we don't have to keep what's broken, broken. If guests are known not to work, we don't worry about how well they migrate. -- MST