Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932518AbcKDUfG (ORCPT ); Fri, 4 Nov 2016 16:35:06 -0400 Received: from mail-qk0-f172.google.com ([209.85.220.172]:33933 "EHLO mail-qk0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751229AbcKDUfD (ORCPT ); Fri, 4 Nov 2016 16:35:03 -0400 MIME-Version: 1.0 In-Reply-To: <20161101013749.4003-8-khuey@kylehuey.com> References: <20161101013749.4003-1-khuey@kylehuey.com> <20161101013749.4003-8-khuey@kylehuey.com> From: David Matlack Date: Fri, 4 Nov 2016 13:34:31 -0700 Message-ID: Subject: Re: [PATCH v8 7/7] KVM: x86: virtualize cpuid faulting To: Kyle Huey Cc: "Robert O'Callahan" , Thomas Gleixner , Andy Lutomirski , Ingo Molnar , "H. Peter Anvin" , X86 ML , Paolo Bonzini , =?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" , user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm list Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6288 Lines: 155 On Mon, Oct 31, 2016 at 6:37 PM, Kyle Huey wrote: > Hardware support for faulting on the cpuid instruction is not required to > emulate it, because cpuid triggers a VM exit anyways. KVM handles the relevant > MSRs (MSR_PLATFORM_INFO and MSR_MISC_FEATURES_ENABLE) and upon a > cpuid-induced VM exit checks the cpuid faulting state and the CPL. > kvm_require_cpl is even kind enough to inject the GP fault for us. > > Signed-off-by: Kyle Huey > --- > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/cpuid.c | 3 +++ > arch/x86/kvm/x86.c | 16 ++++++++++++++++ > 3 files changed, 20 insertions(+) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 4b20f73..4a6e62b 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -592,16 +592,17 @@ struct kvm_vcpu_arch { > u64 pat; > > unsigned switch_db_regs; > unsigned long db[KVM_NR_DB_REGS]; > unsigned long dr6; > unsigned long dr7; > unsigned long eff_db[KVM_NR_DB_REGS]; > unsigned long guest_debug_dr7; > + bool cpuid_fault; > > u64 mcg_cap; > u64 mcg_status; > u64 mcg_ctl; > u64 mcg_ext_ctl; > u64 *mce_banks; > > /* Cache MMIO info */ > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index afa7bbb..ed8436a 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -862,16 +862,19 @@ void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx) > trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx); > } > EXPORT_SYMBOL_GPL(kvm_cpuid); > > void kvm_emulate_cpuid(struct kvm_vcpu *vcpu) > { > u32 function, eax, ebx, ecx, edx; > > + if (vcpu->arch.cpuid_fault && !kvm_require_cpl(vcpu, 0)) > + return; > + > function = eax = kvm_register_read(vcpu, VCPU_REGS_RAX); > ecx = kvm_register_read(vcpu, VCPU_REGS_RCX); > kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx); > kvm_register_write(vcpu, VCPU_REGS_RAX, eax); > kvm_register_write(vcpu, VCPU_REGS_RBX, ebx); > kvm_register_write(vcpu, VCPU_REGS_RCX, ecx); > kvm_register_write(vcpu, VCPU_REGS_RDX, edx); > kvm_x86_ops->skip_emulated_instruction(vcpu); > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index e375235..470c553 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2269,16 +2269,21 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > return 1; > vcpu->arch.osvw.length = data; > break; > case MSR_AMD64_OSVW_STATUS: > if (!guest_cpuid_has_osvw(vcpu)) > return 1; > vcpu->arch.osvw.status = data; > break; > + case MSR_MISC_FEATURES_ENABLES: > + if (data & ~CPUID_FAULT_ENABLE) > + return 1; (Due to my comments below, PLATINFO_CPUID_FAULT will not necessarily be enabled for guests. So this code will need to check if the virtual CPU supports PLATINFO_CPUID_FAULT before enabling CPUID faulting.) > + vcpu->arch.cpuid_fault = !!(data & CPUID_FAULT_ENABLE); > + break; > default: > if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr)) > return xen_hvm_config(vcpu, data); > if (kvm_pmu_is_valid_msr(vcpu, msr)) > return kvm_pmu_set_msr(vcpu, msr_info); > if (!ignore_msrs) { > vcpu_unimpl(vcpu, "unhandled wrmsr: 0x%x data %llx\n", > msr, data); > @@ -2483,16 +2488,25 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > return 1; > msr_info->data = vcpu->arch.osvw.length; > break; > case MSR_AMD64_OSVW_STATUS: > if (!guest_cpuid_has_osvw(vcpu)) > return 1; > msr_info->data = vcpu->arch.osvw.status; > break; > + 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). > + 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. > 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