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Subject: Re: [PATCH v2] KVM: X86: Allow userspace to define the microcode
 version
To:     Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Liran Alon <liran.alon@oracle.com>
References: <1519640239-4428-1-git-send-email-wanpengli@tencent.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <469812b9-d003-249a-d6d3-de74c24e4146@redhat.com>
Date:   Mon, 26 Feb 2018 12:42:28 +0100
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On 26/02/2018 11:17, Wanpeng Li 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>
> Cc: Liran Alon <liran.alon@oracle.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v1 -> v2:
>  * add MSR_IA32_UCODE_REV to emulated_msrs
> 
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/x86.c              | 9 +++++++--
>  2 files changed, 8 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..4ae9517 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1047,6 +1047,7 @@ static u32 emulated_msrs[] = {
>  	MSR_SMI_COUNT,
>  	MSR_PLATFORM_INFO,
>  	MSR_MISC_FEATURES_ENABLES,
> +	MSR_IA32_UCODE_REV,
>  };
>  
>  static unsigned num_emulated_msrs;
> @@ -2247,7 +2248,6 @@ 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 +2255,10 @@ 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;

Please remove the shifts, and add the MSR_IA32_UCODE_REV version to the
"feature MSRs" recently added by Tom Lendacky.

Thanks,

Paolo

> +		break;
>  	case MSR_EFER:
>  		return set_efer(vcpu, data);
>  	case MSR_K7_HWCR:
> @@ -2550,7 +2554,7 @@ 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 +8236,7 @@ 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);
>  }
>