From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: [PATCH] kvm: svm: Only propagate next_rip when guest supports it Date: Wed, 7 Oct 2015 14:47:00 +0200 Message-ID: <20151007124700.GE28811@8bytes.org> References: <560D1C6E.2060803@suse.com> <560D278F.10801@redhat.com> <20151006102838.GD20886@8bytes.org> <20151007110335.GA28811@8bytes.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Paolo Bonzini , kvm@vger.kernel.org, Dirk =?iso-8859-1?Q?M=FCller?= To: Bandan Das Return-path: Received: from 8bytes.org ([81.169.241.247]:46399 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751394AbbJGMrC (ORCPT ); Wed, 7 Oct 2015 08:47:02 -0400 Content-Disposition: inline In-Reply-To: <20151007110335.GA28811@8bytes.org> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Oct 07, 2015 at 01:03:35PM +0200, Joerg Roedel wrote: > But we don't care if L1 writes something into its own next_rip, as we > never read this value from its VMCB. We only copy the next_rip value we > get from our shadow-vmcb to it on an emulated vmexit. So I still don't > understand what triggers the reported problem or why the WARN_ON is > necessary. Okay, I think I have an idea now. I talked a bit with Dirk and the WARN_ON triggers in the guest, and not on the host. This makes a lot more sense. In nested-svm we always copy the next_rip from the shadow-vmcb to the guests vmcb, even when the nrips bit in cpuid is not set for the guest. This obviously triggers the WARN_ON() in the L1 KVM (I still don't understand why the WARN_ON was introduced in the first place). So the right fix is to only copy next_rip to the guests vmcb when its cpuid indicates that next_rip is supported there, like in this patch: >>From 019afc60507618b8e44e0c67d5ea2d850d88c9dd Mon Sep 17 00:00:00 2001 From: Joerg Roedel Date: Wed, 7 Oct 2015 13:38:19 +0200 Subject: [PATCH] kvm: svm: Only propagate next_rip when guest supports it Currently we always write the next_rip of the shadow vmcb to the guests vmcb when we emulate a vmexit. This could confuse the guest when its cpuid indicated no support for the next_rip feature. Fix this by only propagating next_rip if the guest actually supports it. Signed-off-by: Joerg Roedel --- arch/x86/kvm/cpuid.h | 21 +++++++++++++++++++++ arch/x86/kvm/svm.c | 7 ++++++- 2 files changed, 27 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h index dd05b9c..effca1f 100644 --- a/arch/x86/kvm/cpuid.h +++ b/arch/x86/kvm/cpuid.h @@ -133,4 +133,25 @@ static inline bool guest_cpuid_has_mpx(struct kvm_vcpu *vcpu) best = kvm_find_cpuid_entry(vcpu, 7, 0); return best && (best->ebx & bit(X86_FEATURE_MPX)); } + +/* + * NRIPS is provided through cpuidfn 0x8000000a.edx bit 3 + */ +#define BIT_NRIPS 3 + +static inline bool guest_cpuid_has_nrips(struct kvm_vcpu *vcpu) +{ + struct kvm_cpuid_entry2 *best; + + best = kvm_find_cpuid_entry(vcpu, 0x8000000a, 0); + + /* + * NRIPS is a scattered cpuid feature, so we can't use + * X86_FEATURE_NRIPS here (X86_FEATURE_NRIPS would be bit + * position 8, not 3). + */ + return best && (best->edx & bit(BIT_NRIPS)); +} +#undef BIT_NRIPS + #endif diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 94b7d15..e1a8824 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -2459,7 +2459,9 @@ static int nested_svm_vmexit(struct vcpu_svm *svm) nested_vmcb->control.exit_info_2 = vmcb->control.exit_info_2; nested_vmcb->control.exit_int_info = vmcb->control.exit_int_info; nested_vmcb->control.exit_int_info_err = vmcb->control.exit_int_info_err; - nested_vmcb->control.next_rip = vmcb->control.next_rip; + + if (guest_cpuid_has_nrips(vcpu)) + nested_vmcb->control.next_rip = vmcb->control.next_rip; /* * If we emulate a VMRUN/#VMEXIT in the same host #vmexit cycle we have @@ -2714,6 +2716,9 @@ static bool nested_svm_vmrun(struct vcpu_svm *svm) svm->vmcb->control.event_inj = nested_vmcb->control.event_inj; svm->vmcb->control.event_inj_err = nested_vmcb->control.event_inj_err; + /* Clear next_rip, as real hardware would do */ + nested_vmcb->control.next_rip = 0; + nested_svm_unmap(page); /* Enter Guest-Mode */ -- 1.8.4.5