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

From: Wanpeng Li <kernellwp@gmail.com>
To: Liran Alon <liran.alon@oracle.com>
Cc: Radim Krcmar <rkrcmar@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version
Date: Mon, 26 Feb 2018 18:08:14 +0800	[thread overview]
Message-ID: <CANRm+CwE1SSU_WWrJZKTkCR62WUdRrPex0=CjgrL4LExsmbOdQ@mail.gmail.com> (raw)
In-Reply-To: <1f6d0e8e-6d76-4262-9e8b-f8b1f23d8248@default>

2018-02-26 17:26 GMT+08:00 Liran Alon <liran.alon@oracle.com>:
>
> ----- kernellwp@gmail.com wrote:
>
>> From: Wanpeng Li <wanpengli@tencent.com>
>>
>> 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@amazon.de>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
>> ---
>>  arch/x86/include/asm/kvm_host.h | 1 +
>>  arch/x86/kvm/x86.c              | 8 ++++++--
>>  2 files changed, 7 insertions(+), 2 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 1a3ed81..cc51c61 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2247,7 +2247,6 @@ 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:
>> @@ -2255,6 +2254,10 @@ 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 >> 32;
>> +             break;
>>       case MSR_EFER:
>>               return set_efer(vcpu, data);
>>       case MSR_K7_HWCR:
>> @@ -2550,7 +2553,7 @@ 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 << 32;
>>               break;
>>       case MSR_MTRRcap:
>>       case 0x200 ... 0x2ff:
>> @@ -8232,6 +8235,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool
>> init_event)
>>       vcpu->arch.regs_dirty = ~0;
>>
>>       vcpu->arch.ia32_xss = 0;
>> +     vcpu->arch.microcode_version = 0x1;
>>
>>       kvm_x86_ops->vcpu_reset(vcpu, init_event);
>>  }
>> --
>> 2.7.4
>
> I think you need to add MSR_IA32_UCODE_REV to emulated_msrs[]
> to allow for proper live-migration of this MSR value.

Good catch, will do in v2.

Regards,
Wanpeng Li