Re: [PATCH v3] KVM: X86: Allow userspace to define the microcode version

[Wanpeng Li]

2018-02-27 9:30 GMT+08:00 Nadav Amit <nadav.amit@xxxxxxxxx>:
> Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
>
>> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>>
>> Linux (among the others) has checks to make sure that certain features
>> aren't enabled on a certain family/model/stepping if the microcode version
>> isn't greater than or equal to a known good version.
>>
>> By exposing the real microcode version, we're preventing buggy guests that
>> don't check that they are running virtualized (i.e., they should trust the
>> hypervisor) from disabling features that are effectively not buggy.
>>
>> Suggested-by: Filippo Sironi <sironi@xxxxxxxxx>
>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
>> Cc: Liran Alon <liran.alon@xxxxxxxxxx>
>> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>> ---
>> v2 -> v3:
>> * remove the shifts
>> * add the MSR_IA32_UCODE_REV version to the "feature MSRs"
>> v1 -> v2:
>> * add MSR_IA32_UCODE_REV to emulated_msrs
>>
>> arch/x86/include/asm/kvm_host.h |  1 +
>> arch/x86/kvm/x86.c              | 19 +++++++++++++++----
>> 2 files changed, 16 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 938d453..6e13f2f 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -507,6 +507,7 @@ struct kvm_vcpu_arch {
>>       u64 smi_count;
>>       bool tpr_access_reporting;
>>       u64 ia32_xss;
>> +     u32 microcode_version;
>>
>>       /*
>>        * Paging state of the vcpu
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index d4985a9..00af28e 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1058,6 +1058,7 @@ static unsigned num_emulated_msrs;
>> static u32 msr_based_features[] = {
>>       MSR_IA32_ARCH_CAPABILITIES,
>>       MSR_F10H_DECFG,
>> +     MSR_IA32_UCODE_REV,
>> };
>>
>> static unsigned int num_msr_based_features;
>> @@ -1067,8 +1068,14 @@ static int do_get_msr_feature(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
>>       struct kvm_msr_entry msr;
>>
>>       msr.index = index;
>> -     if (kvm_x86_ops->get_msr_feature(&msr))
>> -             return 1;
>> +     switch (msr.index) {
>> +     case MSR_IA32_UCODE_REV:
>> +             rdmsrl(msr.index, msr.data);
>> +             break;
>> +     default:
>> +             if (kvm_x86_ops->get_msr_feature(&msr))
>> +                     return 1;
>> +     }
>>
>>       *data = msr.data;
>>
>> @@ -2248,7 +2255,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>
>>       switch (msr) {
>>       case MSR_AMD64_NB_CFG:
>> -     case MSR_IA32_UCODE_REV:
>>       case MSR_IA32_UCODE_WRITE:
>>       case MSR_VM_HSAVE_PA:
>>       case MSR_AMD64_PATCH_LOADER:
>> @@ -2256,6 +2262,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>       case MSR_AMD64_DC_CFG:
>>               break;
>>
>> +     case MSR_IA32_UCODE_REV:
>> +             if (msr_info->host_initiated)
>> +                     vcpu->arch.microcode_version = data;
>> +             break;
>>       case MSR_EFER:
>>               return set_efer(vcpu, data);
>>       case MSR_K7_HWCR:
>> @@ -2551,7 +2561,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>               msr_info->data = 0;
>>               break;
>>       case MSR_IA32_UCODE_REV:
>> -             msr_info->data = 0x100000000ULL;
>> +             msr_info->data = (u64)vcpu->arch.microcode_version;
>
> I think that the shifts are missing here (the version should be on the high
> bits according to intel_get_microcode_revision() ).

You are right, it seems that we all miss it before.

Regards,
Wanpeng Li