From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCHv4 3/4] cpuid: disable pv eoi for 1.1 and older compat types Date: Wed, 29 Aug 2012 16:40:21 +0300 Message-ID: <20120829134021.GB32728@redhat.com> References: <877gshu8f5.fsf@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Michael S. Tsirkin" , avi@redhat.com, mtosatti@redhat.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, Jan Kiszka , Blue Swirl To: Anthony Liguori Return-path: Received: from mx1.redhat.com ([209.132.183.28]:28590 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753712Ab2H2Nkb (ORCPT ); Wed, 29 Aug 2012 09:40:31 -0400 Content-Disposition: inline In-Reply-To: <877gshu8f5.fsf@codemonkey.ws> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Aug 29, 2012 at 08:36:30AM -0500, Anthony Liguori wrote: > "Michael S. Tsirkin" writes: > > > In preparation for adding PV EOI support, disable PV EOI by default for > > 1.1 and older machine types, to avoid CPUID changing during migration. > > > > PV EOI can still be enabled/disabled by specifying it explicitly. > > Enable for 1.1 > > -M pc-1.1 -cpu kvm64,+kvm_pv_eoi > > Disable for 1.2 > > -M pc-1.2 -cpu kvm64,-kvm_pv_eoi > > > > Signed-off-by: Michael S. Tsirkin > > As best I can tell, we're papering over an ABI breakage in KVM. > > If an old QEMU attempts to do a live migration on a new kernel, > migrating to an QEMU on a different box with an older kernel, it will > fail because there is state that isn't being migrated. > > This ought to be fixed in the kernel by making these features > whitelisted by userspace. > What do you mean. Userspace and only userspace decides what cpuid bits will be seen by a guest. Currently userspace enables all PV cpuid bits it finds. -- Gleb.