linux-kernel - Re: [PATCH v5 4/8] KVM: VMX: Pass through CET related MSRs to Guest

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Message-ID: <20190604195902.GB7476@linux.intel.com>
Date:   Tue, 4 Jun 2019 12:59:02 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, mst@...hat.com, rkrcmar@...hat.com,
        jmattson@...gle.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, yu-cheng.yu@...el.com
Subject: Re: [PATCH v5 4/8] KVM: VMX: Pass through CET related MSRs to Guest

On Wed, May 22, 2019 at 03:00:57PM +0800, Yang Weijiang wrote:
> CET MSRs pass through Guest directly to enhance performance.
> CET runtime control settings are stored in MSR_IA32_{U,S}_CET,
> Shadow Stack Pointer(SSP) are presented in MSR_IA32_PL{0,1,2,3}_SSP,
> SSP table base address is stored in MSR_IA32_INT_SSP_TAB,
> these MSRs are defined in kernel and re-used here.
> 
> MSR_IA32_U_CET and MSR_IA32_PL3_SSP are used for user mode protection,
> the contents could differ from process to process, therefore,
> kernel needs to save/restore them during context switch, so it makes
> sense to pass through them so that the guest kernel can
> use xsaves/xrstors to operate them efficiently. Ohter MSRs are used
> for non-user mode protection. See CET spec for detailed info.
> 
> The difference between CET VMCS state fields and xsave components is,
> the former used for CET state storage during VMEnter/VMExit,
> whereas the latter used for state retention between Guest task/process
> switch.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> Co-developed-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 574428375ff9..9321da538f65 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6942,6 +6942,7 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
>  static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +	unsigned long *msr_bitmap;
>  
>  	if (cpu_has_secondary_exec_ctrls()) {
>  		vmx_compute_secondary_exec_control(vmx);
> @@ -6963,6 +6964,19 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
>  	if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
>  			guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT))
>  		update_intel_pt_cfg(vcpu);
> +
> +	msr_bitmap = vmx->vmcs01.msr_bitmap;
> +
> +	if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
> +	    guest_cpuid_has(vcpu, X86_FEATURE_IBT)) {
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL1_SSP, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_SSP, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW);
> +	}
>  }
>  
>  static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
> @@ -7163,6 +7177,7 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
>  		spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
>  		vcpu->pre_pcpu = -1;
>  	}
> +

Spurious whitespace change.

>  }
>  
>  /*
> -- 
> 2.17.2
>