From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758128AbcGKI4s (ORCPT ); Mon, 11 Jul 2016 04:56:48 -0400 Received: from mail-oi0-f51.google.com ([209.85.218.51]:33120 "EHLO mail-oi0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751847AbcGKI4o (ORCPT ); Mon, 11 Jul 2016 04:56:44 -0400 Subject: Re: [PATCH v2 11/13] KVM: x86: add KVM_CAP_X2APIC_API To: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <20160707171550.14675-1-rkrcmar@redhat.com> <20160707171550.14675-12-rkrcmar@redhat.com> <630f1159-53b4-aeca-ed36-c94e9bf75790@gmail.com> <053e042b-c523-9c10-51e5-59a5ac164bc5@redhat.com> Cc: "Lan, Tianyu" , Igor Mammedov , Jan Kiszka , Peter Xu From: Yang Zhang Message-ID: <26250689-9263-58a0-7700-1fa83a1dc96e@gmail.com> Date: Mon, 11 Jul 2016 16:56:39 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <053e042b-c523-9c10-51e5-59a5ac164bc5@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016/7/11 15:44, Paolo Bonzini wrote: > > > On 11/07/2016 08:06, Yang Zhang wrote: >>> Changes to MSI addresses follow the format used by interrupt remapping >>> unit. >>> The upper address word, that used to be 0, contains upper 24 bits of >>> the LAPIC >>> address in its upper 24 bits. Lower 8 bits are reserved as 0. >>> Using the upper address word is not backward-compatible either as we >>> didn't >>> check that userspace zeroed the word. Reserved bits are still not >>> explicitly >> >> Does this means we cannot migrate the VM from KVM_CAP_X2APIC_API enabled >> host to the disable host even VM doesn't have more than 255 VCPUs? > > Yes, but that's why KVM_CAP_X2APIC_API is enabled manually. The idea is > that QEMU will not use KVM_CAP_X2APIC_API except on the newest machine type. Thanks for confirmation. And when the KVM_CAP_X2APIC_API will be enabled in Qemu? > > If interrupt remapping is on, KVM_CAP_X2APIC_API is needed even with 8 > VCPUs, I think. Otherwise KVM will believe that 0xff is "broadcast" > rather than "cluster 0, CPUs 0-7". If interrupt remapping is using, what 0xff means is relying on which mode the destination CPU is in. I think there is no KVM_CAP_X2APIC_API needed since interrupt remapping table gives all the information. -- best regards yang