Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761937AbcKDV5e (ORCPT ); Fri, 4 Nov 2016 17:57:34 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35944 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753226AbcKDV5c (ORCPT ); Fri, 4 Nov 2016 17:57:32 -0400 Subject: Re: [PATCH v8 7/7] KVM: x86: virtualize cpuid faulting To: David Matlack , Kyle Huey References: <20161101013749.4003-1-khuey@kylehuey.com> <20161101013749.4003-8-khuey@kylehuey.com> Cc: "Robert O'Callahan" , Thomas Gleixner , Andy Lutomirski , Ingo Molnar , "H. Peter Anvin" , X86 ML , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Jeff Dike , Richard Weinberger , Alexander Viro , Shuah Khan , Dave Hansen , Borislav Petkov , Peter Zijlstra , Boris Ostrovsky , Len Brown , "Rafael J. Wysocki" , Dmitry Safonov , linux-kernel@vger.kernel.org, Eduardo Habkost From: Paolo Bonzini Message-ID: Date: Fri, 4 Nov 2016 22:57:27 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: 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 Content-Length: 2806 Lines: 74 On 04/11/2016 21:34, David Matlack wrote: > On Mon, Oct 31, 2016 at 6:37 PM, Kyle Huey wrote: >> + case MSR_PLATFORM_INFO: >> + /* cpuid faulting is supported */ >> + msr_info->data = PLATINFO_CPUID_FAULT; >> + break; > > This could break save/restore, if for example, a VM is migrated to a > version of KVM without MSR_PLATFORM_INFO support. I think the way to > handle this is to make MSR_PLATFORM_INFO writeable (but only from > userspace) so that hypervisors can defend themselves (by setting this > MSR to 0). Right---and with my QEMU hat on, this feature will have to be enabled manually on the command line because of the way QEMU supports running with old kernels. :( This however does not impact the KVM patch. We may decide that, because CPUID faulting doesn't have a CPUID bit and is relatively a "fringe" feature, we are okay if the kernel enables this unconditionally and then userspace can arrange to block migration (in QEMU this would use a subsection). David, Eduardo, opinions? > >> + case MSR_MISC_FEATURES_ENABLES: >> + msr_info->data = 0; >> + if (vcpu->arch.cpuid_fault) >> + msr_info->data |= CPUID_FAULT_ENABLE; >> + break; > > MSR_MISC_FEATURES_ENABLES should be added to emulated_msrs[] so that > the hypervisor will maintain the value of CPUID_FAULT_ENABLE across a > save/restore. This is definitely necessary. Thanks David. Paolo >> default: >> if (kvm_pmu_is_valid_msr(vcpu, msr_info->index)) >> return kvm_pmu_get_msr(vcpu, msr_info->index, &msr_info->data); >> if (!ignore_msrs) { >> vcpu_unimpl(vcpu, "unhandled rdmsr: 0x%x\n", msr_info->index); >> return 1; >> } else { >> vcpu_unimpl(vcpu, "ignored rdmsr: 0x%x\n", msr_info->index); >> @@ -7493,16 +7507,18 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) >> kvm_update_dr0123(vcpu); >> vcpu->arch.dr6 = DR6_INIT; >> kvm_update_dr6(vcpu); >> vcpu->arch.dr7 = DR7_FIXED_1; >> kvm_update_dr7(vcpu); >> >> vcpu->arch.cr2 = 0; >> >> + vcpu->arch.cpuid_fault = false; >> + >> kvm_make_request(KVM_REQ_EVENT, vcpu); >> vcpu->arch.apf.msr_val = 0; >> vcpu->arch.st.msr_val = 0; >> >> kvmclock_reset(vcpu); >> >> kvm_clear_async_pf_completion_queue(vcpu); >> kvm_async_pf_hash_reset(vcpu); >> -- >> 2.10.2 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe kvm" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >