Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752484AbaF2Gqe (ORCPT ); Sun, 29 Jun 2014 02:46:34 -0400 Received: from mail-we0-f171.google.com ([74.125.82.171]:49632 "EHLO mail-we0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752423AbaF2Gqc (ORCPT ); Sun, 29 Jun 2014 02:46:32 -0400 Date: Sun, 29 Jun 2014 09:46:27 +0300 From: Gleb Natapov To: Borislav Petkov Cc: Paolo Bonzini , lkml , Peter Zijlstra , Steven Rostedt , x86-ml , kvm@vger.kernel.org, =?utf-8?B?SsO2cmcgUsO2ZGVs?= Subject: Re: __schedule #DF splat Message-ID: <20140629064626.GD18167@minantech.com> References: <20140625153227.GA13845@pd.tnic> <20140625202650.GC13845@pd.tnic> <20140627101831.GB23153@pd.tnic> <53AD586A.40900@redhat.com> <20140627115545.GC23153@pd.tnic> <53AD5D27.2090505@redhat.com> <20140627121053.GD23153@pd.tnic> <20140628114431.GB4373@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140628114431.GB4373@pd.tnic> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 28, 2014 at 01:44:31PM +0200, Borislav Petkov wrote: > qemu-system-x86-20240 [006] ...1 9406.484134: kvm_page_fault: address 7fffb62ba318 error_code 2 > qemu-system-x86-20240 [006] ...1 9406.484136: kvm_inj_exception: #PF (0x2)a > > kvm injects the #PF into the guest. > > qemu-system-x86-20240 [006] d..2 9406.484136: kvm_entry: vcpu 1 > qemu-system-x86-20240 [006] d..2 9406.484137: kvm_exit: reason PF excp rip 0xffffffff8161130f info 2 7fffb62ba318 > qemu-system-x86-20240 [006] ...1 9406.484138: kvm_page_fault: address 7fffb62ba318 error_code 2 > qemu-system-x86-20240 [006] ...1 9406.484141: kvm_inj_exception: #DF (0x0) > > Second #PF at the same address and kvm injects the #DF. > > BUT(!), why? > > I probably am missing something but WTH are we pagefaulting at a > user address in context_switch() while doing a lockdep call, i.e. > spin_release? We're not touching any userspace gunk there AFAICT. > > Is this an async pagefault or so which kvm is doing so that the guest > rip is actually pointing at the wrong place? > There is nothing in the trace that point to async pagefault as far as I see. > Or something else I'm missing, most probably... > Strange indeed. Can you also enable kvmmmu tracing? You can also instrument kvm_multiple_exception() to see which two exception are combined into #DF. -- Gleb. -- 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/