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

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Message-ID: <1f6d0e8e-6d76-4262-9e8b-f8b1f23d8248@default>
Date:   Mon, 26 Feb 2018 01:26:19 -0800 (PST)
From:   Liran Alon <liran.alon@...cle.com>
To:     <kernellwp@...il.com>
Cc:     <rkrcmar@...hat.com>, <pbonzini@...hat.com>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version


----- kernellwp@...il.com wrote:

> From: Wanpeng Li <wanpengli@...cent.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@...zon.de>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.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.

The rest seems fine to me. :)

Regards,
-Liran