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SubjectRe: [PATCH 9/8] KVM: x86: limit MSR_IA32_SPEC_CTRL access based on CPUID availability
On Tue, 9 Jan 2018, Paolo Bonzini wrote:
> MSR_IA32_SPEC_CTRL is not available unless CPU[7,0].EDX[26] is 1.
> Check that against host CPUID or guest CPUID, respectively for
> host-initiated and guest-initiated accesses.

Hi Radim, Paolo:

In porting this patch series to v4.14, I'm getting this BUILD_BUG_ON:

In file included from arch/x86/kvm/vmx.c:21:0:
In function 'x86_feature_cpuid',
inlined from 'guest_cpuid_get_register' at arch/x86/kvm/cpuid.h:72:25,
inlined from 'vmx_get_msr' at arch/x86/kvm/cpuid.h:101:6:
arch/x86/kvm/cpuid.h:64:232: error: call to '__compiletime_assert_64'
declared with attribute error: BUILD_BUG_ON failed:
reverse_cpuid[x86_leaf].function == 0
BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);

^
In function 'x86_feature_cpuid',
inlined from 'guest_cpuid_get_register' at arch/x86/kvm/cpuid.h:72:25,
inlined from 'vmx_set_msr' at arch/x86/kvm/cpuid.h:101:6:
arch/x86/kvm/cpuid.h:64:232: error: call to '__compiletime_assert_64'
declared with attribute error: BUILD_BUG_ON failed:
reverse_cpuid[x86_leaf].function == 0
BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);


I think this is caused by the following call stack for
X86_FEATURE_SPEC_CTRL, but if not please correct me here:

arch/x86/kvm/vmx.c:
vmx_get_msr/vmx_set_msr()
guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)
guest_cpuid_get_register(vcpu, x86_feature);
x86_feature_cpuid(x86_feature);
x86_feature_cpuid(unsigned x86_feature)
BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);


It looks like I need to add something to reverse_cpuid[] but I'm not sure
what.

Do you know what needs to be added here?

-Eric

--
Eric Wheeler



>
> Suggested-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> This is for after X86_FEATURE_SPEC_CTRL is added to Linux, but
> I still wanted to ack Jim's improvement.
>
> arch/x86/kvm/svm.c | 8 ++++++++
> arch/x86/kvm/vmx.c | 8 ++++++++
> 2 files changed, 16 insertions(+)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 97126c2bd663..3a646580d7c5 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3648,6 +3648,10 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> msr_info->data = svm->nested.vm_cr_msr;
> break;
> case MSR_IA32_SPEC_CTRL:
> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> + (!msr_info->host_initiated &&
> + !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
> + return 1;
> msr_info->data = svm->spec_ctrl;
> break;
> case MSR_IA32_UCODE_REV:
> @@ -3806,6 +3810,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
> vcpu_unimpl(vcpu, "unimplemented wrmsr: 0x%x data 0x%llx\n", ecx, data);
> break;
> case MSR_IA32_SPEC_CTRL:
> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> + (!msr_info->host_initiated &&
> + !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
> + return 1;
> svm->spec_ctrl = data;
> break;
> case MSR_IA32_APICBASE:
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 49b4a2d61603..42bc7ee293e4 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3368,6 +3368,10 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> msr_info->data = guest_read_tsc(vcpu);
> break;
> case MSR_IA32_SPEC_CTRL:
> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> + (!msr_info->host_initiated &&
> + !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
> + return 1;
> msr_info->data = to_vmx(vcpu)->spec_ctrl;
> break;
> case MSR_IA32_SYSENTER_CS:
> @@ -3510,6 +3514,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> kvm_write_tsc(vcpu, msr_info);
> break;
> case MSR_IA32_SPEC_CTRL:
> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> + (!msr_info->host_initiated &&
> + !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
> + return 1;
> to_vmx(vcpu)->spec_ctrl = data;
> break;
> case MSR_IA32_CR_PAT:
> --
> 1.8.3.1
>
>

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