On Mon, Jul 22, 2013 at 07:24:24PM +0800, Peter Huang(Peng) wrote: > Hi, Everyone > > I have been encountered a problem recently. > My box uses Nehalem E5520 CPU, and this model doesn't support x2apic feature. > I created a VM on KVM, and uses cpu mode=pass-through, I can get the right cpu > model from the VM, but I can also see that the CPU in the vm supports x2apic. > > This seems werid. > From QEMU's CPU model definition, Nehalem also doesn't support x2apic. > > Can anyone explain it? > libvirt's "host-passthrough" uses "-cpu host', and it "-cpu host" enables every feature that can be enabled on the host. As KVM x2apic emulation doesn't require host CPU support, it gets enabled. If the behavior of "-cpu host" doesn't match libvirt expectations, we need to clarify what are the requirements, and maybe have a "try to be close to host CPU mode" as opposed to the current "enable everything that can be enabled" mode. -- Eduardo -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list