Am 28.05.2013 18:46, schrieb Paolo Bonzini: > Il 28/05/2013 18:34, Bandan Das ha scritto: >> Eduardo Habkost <ehabk...@redhat.com> writes: >> >>> On Mon, May 27, 2013 at 02:21:36PM +0200, Paolo Bonzini wrote: >>>> Il 27/05/2013 14:09, Eduardo Habkost ha scritto: >>>>> On Sat, May 25, 2013 at 08:25:49AM +0200, Paolo Bonzini wrote: >>>>>> Il 25/05/2013 03:21, Bandan Das ha scritto: >>>>>>> There is one user-visible effect: "-cpu ...,enforce" will stop failing >>>>>>> because of missing KVM support for CPUID_EXT_MONITOR. But that's exactly >>>>>>> the point: there's no point in having CPU model definitions that would >>>>>>> never work as-is with neither TCG or KVM. This patch is changing the >>>>>>> meaning of (e.g.) "-machine ...,accel=kvm -cpu Opteron_G3" to match what >>>>>>> was already happening in practice. >>>>>> >>>>>> But then -cpu Opteron_G3 does not match a "real" Opteron G3. Is it >>>>>> worth it? >>>>> >>>>> No models match a "real" CPU this way, because neither TCG or KVM >>>>> support all features supported by a real CPU. I ask the opposite >>>>> question: is it worth maintaining an "accurate" CPU model definition >>>>> that would never work without feature-bit tweaking in the command-line? >>>> >>>> It would work with TCG. Changing TCG to KVM should not change hardware >>>> if you use "-cpu ...,enforce", so it is right that it fails when >>>> starting with KVM. >>>> >>> >>> Changing between KVM and TCG _does_ change hardware, today (with or >>> without check/enforce). All CPU models on TCG have features not >>> supported by TCG automatically removed. See the "if (!kvm_enabled())" >>> block at x86_cpu_realizefn(). >> >> Yes, this is exactly why I was inclined to remove the monitor flag. >> We already have uses of kvm_enabled() to set (or remove) kvm specific stuff, >> and this change is no different. > > Do any of these affect something that is part of x86_def_t?
The vendor comes to mind. Andreas >> I can see Paolo's point though, having >> a common definition probably makes sense too. > >>> (That's why I argue that we need separate classes/names for TCG and KVM >>> modes. Otherwise our predefined models get less useful as they will >>> require low-level feature-bit fiddling on the libvirt side to make them >>> work as expected.) >> >> Agreed. From a user's perspective, I think the more a CPU model "just works", >> whether it's KVM or TCG, the better. > > Yes, that's right. But I think extending the same expectation to "-cpu > ...,enforce" is not necessary, and perhaps even wrong for "-cpu > ...,check" since it's only a warning rather than a fatal error. > > Paolo > -- SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
