From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757305Ab3DAF0M (ORCPT ); Mon, 1 Apr 2013 01:26:12 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:34836 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756205Ab3DAF0K (ORCPT ); Mon, 1 Apr 2013 01:26:10 -0400 Message-ID: <51591A8A.1060904@oracle.com> Date: Mon, 01 Apr 2013 13:26:34 +0800 From: Zhenzhong Duan Reply-To: zhenzhong.duan@oracle.com Organization: oracle User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130307 Thunderbird/17.0.4 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: "linux-kernel@vger.kernel.org" , Feng Jin , Tamon Shiose Subject: Re: [PATCH] xen: Don't call arch_trigger_all_cpu_backtrace in dom0(pvm) References: <5155413E.6090002@oracle.com> <20130329134640.GG31356@phenom.dumpdata.com> In-Reply-To: <20130329134640.GG31356@phenom.dumpdata.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2013-03-29 21:46, Konrad Rzeszutek Wilk wrote: > On Fri, Mar 29, 2013 at 03:22:38PM +0800, Zhenzhong Duan wrote: >> nmi isn't supported in dom0, fallback to general all cpu backtrace code. >> >> Without fix, on xapic system, sysrq+l, no backtrace is showed. >> On x2apic enabled system, got NULL pointer dereference as below. > Why would the x2APIC or xAPIC make a difference here? The Linux dom0 > is not fiddling with the APIC - that is the hypervisor job. In x2apic enabled system, dom0 kernel set apic pointer to apic_x2apic_cluster or apic_x2apic_phys. When sending nmi, apic->send_IPI_all copy cpumask which isn't initialized. For xapic system, apic->send_IPI_all=xen_send_IPI_all apic, this func does nothing for nmi, so no backtrace. > Can you explain to me why x2apic_send_IPI_mask is even set? Wouldn't > the Xen version of send_IPI be present? (See xen_smp_ops) It's overwrited by x2apic initialization. The problem is even without overwrite, like xapic system, xen_send_IPI_all doesn't work for nmi vector. zduan