From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51133) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xr8d7-0002J8-83 for qemu-devel@nongnu.org; Wed, 19 Nov 2014 12:01:30 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xr8cy-0006RF-83 for qemu-devel@nongnu.org; Wed, 19 Nov 2014 12:01:21 -0500 Received: from mail-wi0-x22e.google.com ([2a00:1450:400c:c05::22e]:53631) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xr8cy-0006R6-0s for qemu-devel@nongnu.org; Wed, 19 Nov 2014 12:01:12 -0500 Received: by mail-wi0-f174.google.com with SMTP id h11so6071869wiw.13 for ; Wed, 19 Nov 2014 09:01:11 -0800 (PST) Sender: Paolo Bonzini Message-ID: <546CCCD2.8050507@redhat.com> Date: Wed, 19 Nov 2014 18:01:06 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <1416254843-16859-3-git-send-email-mst@redhat.com> <546AE14E.7060606@redhat.com> <20141118074904.GA19745@redhat.com> <87y4r7o8dh.fsf@elfo.elfo> <20141119093320.GA26119@redhat.com> <87d28jo5yp.fsf@elfo.elfo> <20141119102136.GC26395@redhat.com> <878uj7o4ec.fsf@elfo.elfo> <20141119132851.GA27435@redhat.com> <546C9EC0.5000105@redhat.com> <20141119162712.GA19365@morn.localdomain> In-Reply-To: <20141119162712.GA19365@morn.localdomain> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 2/5] exec: qemu_ram_alloc_device, qemu_ram_resize List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin O'Connor Cc: "Michael S. Tsirkin" , qemu-devel@nongnu.org, dgilbert@redhat.com, Juan Quintela On 19/11/2014 17:27, Kevin O'Connor wrote: > On Wed, Nov 19, 2014 at 02:44:32PM +0100, Paolo Bonzini wrote: >> So: >> >> qemu-2.0 -M pc-2.0 -> qemu-2.2 -M pc-2.0 >> >> uses 2.0 BIOS >> >> qemu-2.2 -M pc-2.0 -> qemu-2.0 -M pc-2.0 >> >> uses 2.2 BIOS >> >> Both should work, in general. BIOS is rarely the reason for >> incompatibilities. However, breakage can happen, for example I know >> that RHEL7 SeaBIOS does not work on RHEL6. RHEL6 SeaBIOS works on >> RHEL7, but it needs a couple workarounds. > > Do you know why that is? We do try to make SeaBIOS backwards > compatible with older versions of QEMU. For RHEL6-on-RHEL7 SeaBIOS was violating the virtio-scsi spec, but QEMU happened to support the broken case until recently. When I was told that the broken case stopped working, I added a workaround. I don't know why RHEL7 SeaBIOS does not work on RHEL6. But note that it's a really old version (0.12). I guess one could try compiling various QEMU versions and see where it broke, and then either debug or bisect further. RHEL7 uses 1.5.3. Paolo