Re: [9/8] KVM: x86: limit MSR_IA32_SPEC_CTRL access based on CPUID availability

[Jim Mattson]

All MSR intercepts are enabled by default, so I don't think this patch
does anything at all, unless I'm missing some context.

On Tue, Jan 30, 2018 at 5:21 AM, Mihai Carabas <mihai.carabas@xxxxxxxxxx> wrote:
> Hello Paolo,
>
> I've back ported this patch on 4.1, after adding the per-vcpu MSR bitmap.
> Also enabled the SPEC_CTRL_MSR intercept if qemu instructed so [1].
>
> Reviewed-by: Mihai Carabas <mihai.carabas@xxxxxxxxxx>
>
> [1]
> +++ b/arch/x86/kvm/vmx.c
> @@ -8391,6 +8391,16 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm
> *kvm, unsigned int id)
>         vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PRED_CMD,
> MSR_TYPE_R | MSR_TYPE_W);
>         vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_BNDCFGS,
> MSR_TYPE_R | MSR_TYPE_W);
>
> +       /*
> +        * If the physical CPU or the vCPU of this VM doesn't
> +        * support SPEC_CTRL feature, catch each access to it.
> +        */
> +       if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> +            !guest_cpuid_has_spec_ctrl(&vmx->vcpu))
> +               vmx_enable_intercept_for_msr(
> +                       msr_bitmap,
> +                       MSR_IA32_SPEC_CTRL,
> +                       MSR_TYPE_R | MSR_TYPE_W);
>
>         /*
>          * If PML is turned on, failure on enabling PML just results in
> failure
>
>
>
> On 09.01.2018 14:03, 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.
>>
>> Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> ---
>>         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:
>>
>