Re: [libvirt] [Qemu-devel] [Question] why x2apic's set by default without host support(on Nehalem CPU).

On Tue, Jul 23, 2013 at 10:44:48 +0800, Peter Huang(Peng) wrote: >> libvirt's "host-passthrough" uses "-cpu host', and it "-cpu host" >> enables every feature that can be enabled on the host. > From my test results, I found that even when use host-passthrough mode, VM's > cpu features are very different from host, this doesn't match what host-passthrough > mode's explanation. > > libvirt's option exlanation: > With this mode, the CPU visible to the guest should be exactly the same as the host > CPU even in the aspects that libvirt does not understand. The libvirt documentation is what needs to be updated. While host-passthrough is asking for a CPU which is as close as possible to the real host CPU, there are features that need special handling before they can be provided to a guest. And if the hypervisor does not provide that handling, it may just filter such feature out. Also if some features can be efficiently provided to a guest even though the host CPU does not provide them (x2apic is an example of such feature), they may be provided to a guest. Jirka