From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56301) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1auB-00075C-AA for qemu-devel@nongnu.org; Tue, 23 Jul 2013 07:37:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V1au8-0001RA-Ja for qemu-devel@nongnu.org; Tue, 23 Jul 2013 07:37:23 -0400 Received: from smtp.vivo.cz ([85.132.139.19]:39623) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1akd-0006dm-QS for qemu-devel@nongnu.org; Tue, 23 Jul 2013 07:27:31 -0400 Date: Tue, 23 Jul 2013 13:27:12 +0200 From: Jiri Denemark Message-ID: <20130723112712.GF4718@orkuz.home> References: <51ED1668.7030205@huawei.com> <20130722134138.GE19826@otherpad.lan.raisama.net> <51EDEE20.4060206@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51EDEE20.4060206@huawei.com> Subject: Re: [Qemu-devel] [Question] why x2apic's set by default without host support(on Nehalem CPU). List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Peter Huang(Peng)" Cc: libvir-list@redhat.com, Eduardo Habkost , qemu-devel@nongnu.org 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