From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40851) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1nIr-0001EL-1f for qemu-devel@nongnu.org; Tue, 23 Jul 2013 20:51:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V1nIn-00086A-QM for qemu-devel@nongnu.org; Tue, 23 Jul 2013 20:51:40 -0400 Received: from szxga01-in.huawei.com ([119.145.14.64]:24894) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1nIn-00084q-7I for qemu-devel@nongnu.org; Tue, 23 Jul 2013 20:51:37 -0400 Message-ID: <51EF2469.1090402@huawei.com> Date: Wed, 24 Jul 2013 08:48:41 +0800 From: "Peter Huang(Peng)" MIME-Version: 1.0 References: <51ED1668.7030205@huawei.com> <20130722134138.GE19826@otherpad.lan.raisama.net> <51EDEE20.4060206@huawei.com> <20130723112712.GF4718@orkuz.home> In-Reply-To: <20130723112712.GF4718@orkuz.home> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit 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: Eduardo Habkost , libvir-list@redhat.com, qemu-devel@nongnu.org, Jiri Denemark Hi,Jiri Thanks for replying. So why VM identified different features from host is due to the hypervisor filtering. I will dig into the hypervisor of how it filter features, and update status later. Thanks again. On 2013-07-23 19:27, Jiri Denemark wrote: > 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 >