From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751316AbeAYPhQ (ORCPT ); Thu, 25 Jan 2018 10:37:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35784 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750980AbeAYPhP (ORCPT ); Thu, 25 Jan 2018 10:37:15 -0500 From: Vitaly Kuznetsov To: kvm@vger.kernel.org Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Wanpeng Li , Liran Alon , "Michael S. Tsirkin" , Jason Wang Subject: [PATCH v2] x86/kvm/vmx: do not use vm-exit instruction length for fast MMIO when running nested Date: Thu, 25 Jan 2018 16:37:07 +0100 Message-Id: <20180125153707.29981-1-vkuznets@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I was investigating an issue with seabios >= 1.10 which stopped working for nested KVM on Hyper-V. The problem appears to be in handle_ept_violation() function: when we do fast mmio we need to skip the instruction so we do kvm_skip_emulated_instruction(). This, however, depends on VM_EXIT_INSTRUCTION_LEN field being set correctly in VMCS. However, this is not the case. Intel's manual doesn't mandate VM_EXIT_INSTRUCTION_LEN to be set when EPT MISCONFIG occurs. While on real hardware it was observed to be set, some hypervisors follow the spec and don't set it; we end up advancing IP with some random value. I checked with Microsoft and they confirmed they don't fill VM_EXIT_INSTRUCTION_LEN on EPT MISCONFIG. Fix the issue by doing instruction skip through emulator when running nested. Fixes: 68c3b4d1676d870f0453c31d5a52e7e65c7448ae Suggested-by: Radim Krčmář Suggested-by: Paolo Bonzini Signed-off-by: Vitaly Kuznetsov --- v1 -> v2: inlay X86_FEATURE_HYPERVISOR case with EMULTYPE_SKIP optimization [Paolo Bonzini, Radim Krčmář] --- arch/x86/kvm/vmx.c | 16 +++++++++++++++- arch/x86/kvm/x86.c | 3 ++- 2 files changed, 17 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index c829d89e2e63..e105b439c372 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6563,7 +6563,21 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu) if (!is_guest_mode(vcpu) && !kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) { trace_kvm_fast_mmio(gpa); - return kvm_skip_emulated_instruction(vcpu); + /* + * Doing kvm_skip_emulated_instruction() depends on undefined + * behavior: Intel's manual doesn't mandate + * VM_EXIT_INSTRUCTION_LEN to be set in VMCS when EPT MISCONFIG + * occurs and while on real hardware it was observed to be set, + * other hypervisors (namely Hyper-V) don't set it, we end up + * advancing IP with some random value. Disable fast mmio when + * running nested and keep it for real hardware in hope that + * VM_EXIT_INSTRUCTION_LEN will always be set correctly. + */ + if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) + return kvm_skip_emulated_instruction(vcpu); + else + return x86_emulate_instruction(vcpu, gpa, EMULTYPE_SKIP, + NULL, 0) == EMULATE_DONE; } ret = kvm_mmu_page_fault(vcpu, gpa, PFERR_RSVD_MASK, NULL, 0); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1cec2c62a0b0..930aba87a723 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5703,7 +5703,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, * handle watchpoints yet, those would be handled in * the emulate_ops. */ - if (kvm_vcpu_check_breakpoint(vcpu, &r)) + if (!(emulation_type & EMULTYPE_SKIP) && + kvm_vcpu_check_breakpoint(vcpu, &r)) return r; ctxt->interruptibility = 0; -- 2.14.3