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