linux-kernel - Re: [PATCH v3 7/9] KVM: vmx/pmu: Add Arch LBR emulation and its VMCS field

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Message-ID: <267c408c-6999-649b-d733-8d64f9cf0594@intel.com>
Date:   Thu, 4 Mar 2021 11:02:24 +0800
From:   "Xu, Like" <like.xu@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, wei.w.wang@...el.com,
        Borislav Petkov <bp@...en8.de>, kvm@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH v3 7/9] KVM: vmx/pmu: Add Arch LBR emulation and its VMCS
 field

On 2021/3/4 1:26, Sean Christopherson wrote:
> 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?

Thank you!

I will add "host_lbrctlmsr" field to "struct vcpu_vmx" and
repeat the update/get_debugctlmsr() stuff.

>>   	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
>>