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. 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. Bandan
