Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757174Ab3DAMlX (ORCPT ); Mon, 1 Apr 2013 08:41:23 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:26141 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754874Ab3DAMlW (ORCPT ); Mon, 1 Apr 2013 08:41:22 -0400 Date: Mon, 1 Apr 2013 08:41:18 -0400 From: Konrad Rzeszutek Wilk To: Zhenzhong Duan 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) Message-ID: <20130401124118.GB11995@phenom.dumpdata.com> References: <5155413E.6090002@oracle.com> <20130329134640.GG31356@phenom.dumpdata.com> <51591A8A.1060904@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51591A8A.1060904@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1655 Lines: 38 On Mon, Apr 01, 2013 at 01:26:34PM +0800, Zhenzhong Duan wrote: > > 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. That explanation needs to be part of the git commit. > The problem is even without overwrite, like xapic system, > xen_send_IPI_all doesn't work for nmi vector. Can you tweak the x2apic_mode = 0 in enligthen.c for example? Or clear the X86_FEATURE_X2APIC in the enlighten.c ? (Similar to how the other features are cleared) Wouldn't that stop x2apic_enabled from detecting x2APIC? Sure. > zduan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/