From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v3] enable x2APIC without interrupt remapping under KVM Date: Tue, 30 Jun 2009 22:16:41 +0300 Message-ID: <4A4A6499.9000406@redhat.com> References: <20090629132926.GB20289@redhat.com> <20090630092623.GI20289@redhat.com> <4A4A476C.2070305@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Gleb Natapov , "linux-kernel@vger.kernel.org" , Suresh Siddha , Sheng Yang , "kvm@vger.kernel.org" To: "Eric W. Biederman" Return-path: Received: from mx2.redhat.com ([66.187.237.31]:45879 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756927AbZF3TQ1 (ORCPT ); Tue, 30 Jun 2009 15:16:27 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 06/30/2009 10:08 PM, Eric W. Biederman wrote: >> Can you elaborate? For kvm guests, the hardware is reasonably will implemented >> and if not we will fix it. We need not cripple a feature just because some >> hardware is broken. >> > > The short version is I don't know what work arounds we will ultimately > decide to deploy to work with real hardware. > > I have been seriously contemplating causing a cpu hot-unplug request > to fail if we are in ioapic mode and we have irqs routed to the cpu > that is being unplugged. > Well, obviously we need to disassociate any irqs from such a cpu. Could be done from the kernel or only enforced by the kernel. > Even with perfectly working hardware it is not possible in the general > case to migrate an ioapic irq from one cpu to another outside of an > interrupt handler without without risking dropping an interrupt. > Can't you generate a spurious interrupt immediately after the migration? An extra interrupt shouldn't hurt. > There is no general way to know you have seen the last interrupt > floating around your system. PCI ordering rules don't help because > the ioapics can potentially take an out of band channel. > Can you describe the problem scenario? an ioapic->lapic message delivered to a dead cpu? -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.