From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Roedel, Joerg" Subject: Re: [PATCH] kvm/svm: fix DR interception handling on upcoming AMD CPUs Date: Wed, 9 Feb 2011 13:56:00 +0100 Message-ID: <20110209125600.GC26519@amd.com> References: <1297210949-13240-1-git-send-email-andre.przywara@amd.com> <20110209100115.GB26519@amd.com> <4D526FD0.8000802@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: "avi@redhat.com" , "mtosatti@redhat.com" , "kvm@vger.kernel.org" To: Andre Przywara Return-path: Received: from am1ehsobe005.messaging.microsoft.com ([213.199.154.208]:11778 "EHLO AM1EHSOBE005.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752835Ab1BIM5G (ORCPT ); Wed, 9 Feb 2011 07:57:06 -0500 Content-Disposition: inline In-Reply-To: <4D526FD0.8000802@amd.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Feb 09, 2011 at 05:43:28AM -0500, Andre Przywara wrote: > Roedel, Joerg wrote: > > On Tue, Feb 08, 2011 at 07:22:29PM -0500, Andre Przywara wrote: > >> Somehow the code line advancing the RIP and checking for exceptions > >> got dropped between the post on the ML and the commit. > >> Add it again to let guests boot on upcoming AMD CPUs again. > >> > >> Reported-by: Joerg Roedel > >> Signed-off-by: Andre Przywara > >> --- > >> arch/x86/kvm/svm.c | 1 + > >> 1 files changed, 1 insertions(+), 0 deletions(-) > >> > >> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > >> index 25bd1bc..be06e58 100644 > >> --- a/arch/x86/kvm/svm.c > >> +++ b/arch/x86/kvm/svm.c > >> @@ -2776,6 +2776,7 @@ static int dr_interception(struct vcpu_svm *svm) > >> if (!err) > >> kvm_register_write(&svm->vcpu, reg, val); > >> } > >> + kvm_complete_insn_gp(&svm->vcpu, err); > > > > Any exception check takes presedence over the intercept. So a call to > > skip_emulated_instruction should be sufficient here. > You are right, but I think this way the implementation is cleaner and > more generic. If there is no exception condition detected (err==0), then > the call will just do skip_emulated_instruction anyway. > But as I write this, I see that err is not initialized, so I'd propose > this corrected version of the patch instead. One function call is not less clean than another and this function call has more overhead. Beside that, looking at kvm_set_dr this function only returns 1 if one tries to set dr4 or dr5 while CR4.DE is not set. In this case the function you call here would inject a #GP but architecturally a #UD is required. This problem doesn't matter too much because the exceptions take precedence over the intercept anyway so it is sufficient to call skip_emulated_instruction here. Joerg -- AMD Operating System Research Center Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632