Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754000Ab3DHHmv (ORCPT ); Mon, 8 Apr 2013 03:42:51 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:55759 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751809Ab3DHHmt convert rfc822-to-8bit (ORCPT ); Mon, 8 Apr 2013 03:42:49 -0400 Message-Id: <5162911202000078000CB38E@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 12.0.2 Date: Mon, 08 Apr 2013 08:42:42 +0100 From: "Jan Beulich" To: "xen-devel" , "Konrad Rzeszutek Wilk" , , "linux-kernel@vger.kernel.org" Cc: "Feng Jin" , "Tamon Shiose" Subject: Re: [Xen-devel] [PATCH-v2] xen: Don't call arch_trigger_all_cpu_backtrace in dom0(pvm) References: <51610A25.4010301@oracle.com> In-Reply-To: <51610A25.4010301@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3422 Lines: 89 >>> On 07.04.13 at 07:54, Zhenzhong Duan wrote: > nmi isn't supported in dom0, fallback to general all cpu backtrace code. Since when is sending NMIs not supported, and since when is this Dom0-specific? If you want to deal with this, you should do so properly: Special case sending NMIs in the respective Xen specific code (using VCPUOP_send_nmi), and carry this out in a way not dependent upon running (un)privileged. > Without fix, on xAPIC system, doing sysrq+l, no backtrace is showed, > as xen_send_IPI_all is called and it doesn't support nmi vector. > > On x2APIC enabled system, got NULL pointer dereference as below. > > SysRq : Show backtrace of all active CPUs > BUG: unable to handle kernel NULL pointer dereference at (null) > IP: [] memcpy+0xb/0x120 > Call Trace: > [] ? __x2apic_send_IPI_mask+0x73/0x160 > [] x2apic_send_IPI_all+0x1e/0x20 > [] arch_trigger_all_cpu_backtrace+0x6c/0xb0 > [] ? _raw_spin_lock_irqsave+0x34/0x50 > [] sysrq_handle_showallcpus+0xe/0x10 > [] __handle_sysrq+0x7d/0x140 > [] ? __handle_sysrq+0x140/0x140 > [] write_sysrq_trigger+0x57/0x60 > [] proc_reg_write+0x86/0xc0 > [] vfs_write+0xce/0x190 > [] sys_write+0x55/0x90 > [] system_call_fastpath+0x16/0x1b > > That's because apic points to apic_x2apic_cluster or apic_x2apic_phys > but the basic element like cpumask isn't initialized. That's of course a bug on its own, fixing of which would go under a suitable subject/title. > -v2: Mask x2APIC feature in pvm to avoid overwrite of apic pointer, > update commit message per Konrad's suggestion. > > Signed-off-by: Zhenzhong Duan > Tested-by: Tamon Shiose > --- > arch/x86/xen/enlighten.c | 3 +++ > include/linux/nmi.h | 2 ++ > 2 files changed, 5 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c > index c8e1c7b..12b0718 100644 > --- a/arch/x86/xen/enlighten.c > +++ b/arch/x86/xen/enlighten.c > @@ -386,6 +386,9 @@ static void __init xen_init_cpuid_mask(void) > cpuid_leaf1_edx_mask &= > ~((1 << X86_FEATURE_APIC) | /* disable local APIC */ > (1 << X86_FEATURE_ACPI)); /* disable ACPI */ > + > + cpuid_leaf1_ecx_mask &= ~(1 << (X86_FEATURE_X2APIC % 32)); > + Bottom line - while this part may be fine (under a different title), ... > ax = 1; > cx = 0; > xen_cpuid(&ax, &bx, &cx, &dx); > diff --git a/include/linux/nmi.h b/include/linux/nmi.h > index db50840..b845757 100644 > --- a/include/linux/nmi.h > +++ b/include/linux/nmi.h > @@ -32,6 +32,8 @@ static inline void touch_nmi_watchdog(void) > #ifdef arch_trigger_all_cpu_backtrace > static inline bool trigger_all_cpu_backtrace(void) > { > + if (xen_domain()) > + return false; ... this part clearly isn't. Jan > arch_trigger_all_cpu_backtrace(); > > return true; -- 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/