From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754060AbcGKJRP (ORCPT ); Mon, 11 Jul 2016 05:17:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50494 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750780AbcGKJRN (ORCPT ); Mon, 11 Jul 2016 05:17:13 -0400 Subject: Re: [PATCH v2 11/13] KVM: x86: add KVM_CAP_X2APIC_API To: Yang Zhang , =?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> <26250689-9263-58a0-7700-1fa83a1dc96e@gmail.com> Cc: "Lan, Tianyu" , Igor Mammedov , Jan Kiszka , Peter Xu From: Paolo Bonzini Message-ID: Date: Mon, 11 Jul 2016 11:17:07 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <26250689-9263-58a0-7700-1fa83a1dc96e@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Mon, 11 Jul 2016 09:17:12 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/07/2016 10:56, Yang Zhang wrote: > 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? It could be 2.7 or 2.8. >> >> 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. If you have EIM 0xff never means broadcast, but KVM sees a 0xff in the interrupt route or KVM_SIGNAL_MSI argument and translates it into a broadcast. Paolo