linux-kernel - Re: [RFC PATCH v4 8/8] KVM:x86: Add user-space read/write interface for CET MSRs

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Date:   Tue, 2 Apr 2019 13:35:45 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, kvm@...r.kernel.org, mst@...hat.com,
        rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, yu-cheng.yu@...el.com
Subject: Re: [RFC PATCH v4 8/8] KVM:x86: Add user-space read/write interface
 for CET MSRs

On Mon, Mar 18, 2019 at 11:03:51PM +0800, Yang Weijiang wrote:
> When VMExit occurs, the Guest CET MSRs are stored in two different
> places, U_CET/PL0_SSP/PL1_SSP/PL2_SSP/PL3_SSP are stored in fpu
> xsave area, they are operated by XSAVES/XRSTORS, so before access
> these MSRs, kvm_load_guest_fpu is required to restore them to Host MSRs.
> After finish operation, need to restore Host MSRs by kvm_put_guest_fpu,
> these two functions are call in __msr_io(). S_CET and INTR_SSP_TABLE
> are stored in VMCS fields, so they can be access via vmcs_read/vmcs_write
> directly.

Hmm, the changelog reads like the kvm_load_guest_fpu() behavior is
introduced in this patch.  It should be reworded to make it more obvious
that a previous patch handled that behavior.  Alternatively, just fold
this into said previous patch.

> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/include/asm/msr-index.h |  2 ++
>  arch/x86/kvm/vmx.c               | 42 ++++++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+)
> 
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 298721ff00f4..cc94ab14a946 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -782,6 +782,8 @@
>  #define MSR_IA32_U_CET		0x6a0 /* user mode cet setting */
>  #define MSR_IA32_S_CET		0x6a2 /* kernel mode cet setting */
>  #define MSR_IA32_PL0_SSP	0x6a4 /* kernel shstk pointer */
> +#define MSR_IA32_PL1_SSP	0x6a5 /* ring 1 shstk pointer */
> +#define MSR_IA32_PL2_SSP	0x6a6 /* ring 2 shstk pointer */
>  #define MSR_IA32_PL3_SSP	0x6a7 /* user shstk pointer */
>  #define MSR_IA32_INT_SSP_TAB	0x6a8 /* exception shstk table */
>  
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 816e11a66557..5923b89fe120 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4153,6 +4153,27 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  			return 1;
>  		msr_info->data = vcpu->arch.ia32_xss;
>  		break;
> +	case MSR_IA32_S_CET:
> +		msr_info->data = vmcs_readl(GUEST_S_CET);
> +		break;
> +	case MSR_IA32_U_CET:
> +		rdmsrl(MSR_IA32_U_CET, msr_info->data);
> +		break;
> +	case MSR_IA32_INT_SSP_TAB:
> +		msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
> +		break;
> +	case MSR_IA32_PL0_SSP:
> +		rdmsrl(MSR_IA32_PL0_SSP, msr_info->data);
> +		break;
> +	case MSR_IA32_PL1_SSP:
> +		rdmsrl(MSR_IA32_PL1_SSP, msr_info->data);
> +		break;
> +	case MSR_IA32_PL2_SSP:
> +		rdmsrl(MSR_IA32_PL2_SSP, msr_info->data);
> +		break;
> +	case MSR_IA32_PL3_SSP:
> +		rdmsrl(MSR_IA32_PL3_SSP, msr_info->data);
> +		break;
>  	case MSR_TSC_AUX:
>  		if (!msr_info->host_initiated &&
>  		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
> @@ -4337,6 +4358,27 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		else
>  			clear_atomic_switch_msr(vmx, MSR_IA32_XSS);
>  		break;
> +	case MSR_IA32_S_CET:
> +		vmcs_writel(GUEST_S_CET, data);
> +		break;
> +	case MSR_IA32_U_CET:
> +		wrmsrl(MSR_IA32_U_CET, data);
> +		break;
> +	case MSR_IA32_INT_SSP_TAB:
> +		vmcs_writel(GUEST_INTR_SSP_TABLE, data);
> +		break;
> +	case MSR_IA32_PL0_SSP:
> +		wrmsrl(MSR_IA32_PL0_SSP, data);
> +		break;
> +	case MSR_IA32_PL1_SSP:
> +		wrmsrl(MSR_IA32_PL1_SSP, data);
> +		break;
> +	case MSR_IA32_PL2_SSP:
> +		wrmsrl(MSR_IA32_PL2_SSP, data);
> +		break;
> +	case MSR_IA32_PL3_SSP:
> +		wrmsrl(MSR_IA32_PL3_SSP, data);
> +		break;
>  	case MSR_TSC_AUX:
>  		if (!msr_info->host_initiated &&
>  		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
> -- 
> 2.17.1
>