linux-kernel - Re: [PATCH v1 4/8] kvm:vmx Pass through host CET related MSRs to Guest.

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Date:   Wed, 2 Jan 2019 10:18:43 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com,
        yu-cheng.yu@...el.com, yi.z.zhang@...el.com, hjl.tools@...il.com,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v1 4/8] kvm:vmx  Pass through host CET related MSRs to
 Guest.

On Wed, Dec 26, 2018 at 04:15:28PM +0800, Yang Weijiang wrote:
> During Guest OS execution, it accesses these MSRs to
> configure CET runtime settings.

The changelog needs to explain why it's ok to expose these MSRS to the
guest, e.g. call out which are saved/loaded through the VMCS and which
are saved/loaded via XSAVES/XRSTORS.  And maybe expand "runtime settings"
to elaborate on when most guest kernels will access the MSRs, i.e. to
justify exposing them to the guest.

It should also clarify why IA32_PL1_SSP and IA32_PL2_SSP are NOT exposed
to the guest.

> 
> 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 | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 25fa6bd2fb95..fa2db6248404 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -11550,6 +11550,13 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_CS, MSR_TYPE_RW);
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_ESP, MSR_TYPE_RW);
>  	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_EIP, MSR_TYPE_RW);
> +
> +	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);
> +
>  	vmx->msr_bitmap_mode = 0;
>  
>  	vmx->loaded_vmcs = &vmx->vmcs01;
> -- 
> 2.17.1
>