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Subject: Re: [PATCH RESEND v5 2/2] 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>,
        Nadav Amit <nadav.amit@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Tom Lendacky <thomas.lendacky@amd.com>
References: <1519797811-4560-1-git-send-email-wanpengli@tencent.com>
 <1519797811-4560-2-git-send-email-wanpengli@tencent.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <f1bb8a2e-34d9-d9d7-3f48-6c3a5057a59f@redhat.com>
Date:   Wed, 28 Feb 2018 07:57:35 +0100
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On 28/02/2018 07:03, 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>
> Cc: Nadav Amit <nadav.amit@gmail.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v4 -> v5:
>  * microcode_version be u64 and initialized suitable, remote hte shifts
> v3 -> v4:
>  * add the shifts back
> 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/svm.c              |  4 +---
>  arch/x86/kvm/vmx.c              |  1 +
>  arch/x86/kvm/x86.c              | 11 +++++++++--
>  4 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 938d453..df6720f 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;
> +	u64 microcode_version;
>  
>  	/*
>  	 * Paging state of the vcpu
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index f874798..312f33f 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1907,6 +1907,7 @@ static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  	u32 dummy;
>  	u32 eax = 1;
>  
> +	vcpu->arch.microcode_version = 0x01000065;
>  	svm->spec_ctrl = 0;
>  
>  	if (!init_event) {
> @@ -3962,9 +3963,6 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  
>  		msr_info->data = svm->spec_ctrl;
>  		break;
> -	case MSR_IA32_UCODE_REV:
> -		msr_info->data = 0x01000065;
> -		break;
>  	case MSR_F15H_IC_CFG: {
>  
>  		int family, model;
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 9968906..2cdbea7 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5781,6 +5781,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  	vmx->rmode.vm86_active = 0;
>  	vmx->spec_ctrl = 0;
>  
> +	vcpu->arch.microcode_version = 0x100000000ULL;
>  	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
>  	kvm_set_cr8(vcpu, 0);
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index efc8554..5c93cbc 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;
> @@ -1065,6 +1066,9 @@ static unsigned int num_msr_based_features;
>  static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
>  {
>  	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;
> @@ -2260,7 +2264,6 @@ 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:
> @@ -2268,6 +2271,10 @@ 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:
> @@ -2563,7 +2570,7 @@ 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 = vcpu->arch.microcode_version;
>  		break;
>  	case MSR_MTRRcap:
>  	case 0x200 ... 0x2ff:
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>