linux-kernel - Re: [PATCH v3 5/8] KVM:VMX: Pass through host CET related MSRs to Guest.

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Message-ID: <20190304185326.GE17120@linux.intel.com>
Date:   Mon, 4 Mar 2019 10:53:27 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com,
        yu-cheng.yu@...el.com, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v3 5/8] KVM:VMX: Pass through host CET related MSRs to
 Guest.

On Mon, Feb 25, 2019 at 09:27:13PM +0800, Yang Weijiang wrote:
> The CET runtime settings, i.e., CET state control bits(IA32_U_CET/
> IA32_S_CET), CET SSP(IA32_PL3_SSP/IA32_PL0_SSP) and SSP table address
> (IA32_INTERRUPT_SSP_TABLE_ADDR) are task/thread specific, therefore,
> OS needs to save/restore the states properly during context switch,
> e.g., task/thread switching, interrupt/exception handling, it uses
> xsaves/xrstors to achieve that.
> 
> The difference between VMCS CET area fields and xsave CET area, is that
> the former is for state retention during Guest/Host context
> switch while the latter is for state retention during OS execution.
> 
> Linux currently doesn't support CPL1 and CPL2, so SSPs for these level
> are skipped here.

But don't we want to allow a guest to access the MSRs regardless of
the host kernel's behavior?

> Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/kvm/vmx.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 7bbb8b26e901..89ee086e1729 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -11769,6 +11769,7 @@ static void nested_vmx_entry_exit_ctls_update(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);
> @@ -11786,6 +11787,18 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
>  		nested_vmx_cr_fixed1_bits_update(vcpu);
>  		nested_vmx_entry_exit_ctls_update(vcpu);
>  	}
> +
> +	msr_bitmap = vmx->vmcs01.msr_bitmap;
> +
> +	if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) |

This should be a logical OR, not a bitwise OR.

> +	    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_PL3_SSP, MSR_TYPE_RW);
> +	}
> +
>  }
>  
>  static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
> -- 
> 2.17.1
>