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Date:   Wed, 3 Mar 2021 09:26:05 -0800
From:   Sean Christopherson <seanjc@google.com>
To:     Like Xu <like.xu@linux.intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Kan Liang <kan.liang@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>, wei.w.wang@intel.com,
        Borislav Petkov <bp@alien8.de>, kvm@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 7/9] KVM: vmx/pmu: Add Arch LBR emulation and its VMCS
 field
Message-ID: <YD/GrQAl1NMPHXFj@google.com>
References: <20210303135756.1546253-1-like.xu@linux.intel.com>
 <20210303135756.1546253-8-like.xu@linux.intel.com>
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On Wed, Mar 03, 2021, Like Xu wrote:
> New VMX controls bits for Arch LBR are added. When bit 21 in vmentry_ctrl
> is set, VM entry will write the value from the "Guest IA32_LBR_CTL" guest
> state field to IA32_LBR_CTL. When bit 26 in vmexit_ctrl is set, VM exit
> will clear IA32_LBR_CTL after the value has been saved to the "Guest
> IA32_LBR_CTL" guest state field.

...

> @@ -2529,7 +2532,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  	      VM_EXIT_LOAD_IA32_EFER |
>  	      VM_EXIT_CLEAR_BNDCFGS |
>  	      VM_EXIT_PT_CONCEAL_PIP |
> -	      VM_EXIT_CLEAR_IA32_RTIT_CTL;
> +	      VM_EXIT_CLEAR_IA32_RTIT_CTL |
> +	      VM_EXIT_CLEAR_IA32_LBR_CTL;

So, how does MSR_ARCH_LBR_CTL get restored on the host?  What if the host wants
to keep _its_ LBR recording active while the guest is running?

>  	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_EXIT_CTLS,
>  				&_vmexit_control) < 0)
>  		return -EIO;
> @@ -2553,7 +2557,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  	      VM_ENTRY_LOAD_IA32_EFER |
>  	      VM_ENTRY_LOAD_BNDCFGS |
>  	      VM_ENTRY_PT_CONCEAL_PIP |
> -	      VM_ENTRY_LOAD_IA32_RTIT_CTL;
> +	      VM_ENTRY_LOAD_IA32_RTIT_CTL |
> +	      VM_ENTRY_LOAD_IA32_LBR_CTL;
>  	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_ENTRY_CTLS,
>  				&_vmentry_control) < 0)
>  		return -EIO;
> -- 
> 2.29.2
>