linux-kernel - Re: [PATCH v2 06/15] KVM: vmx/pmu: Emulate MSR_ARCH_LBR

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Date:   Sun, 25 Dec 2022 12:08:27 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Like Xu <like.xu.linux@...il.com>
CC:     <kan.liang@...ux.intel.com>, <wei.w.wang@...el.com>,
        <seanjc@...gle.com>, <pbonzini@...hat.com>, <jmattson@...gle.com>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 06/15] KVM: vmx/pmu: Emulate MSR_ARCH_LBR_CTL for guest
 Arch LBR


On 12/22/2022 7:24 PM, Like Xu wrote:
> On 25/11/2022 12:05 pm, Yang Weijiang wrote:
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index cea8c07f5229..1ae2efc29546 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -2120,6 +2120,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, 
>> struct msr_data *msr_info)
>>                           VM_EXIT_SAVE_DEBUG_CONTROLS)
>>               get_vmcs12(vcpu)->guest_ia32_debugctl = data;
>>   +        /*
>> +         * For Arch LBR, IA32_DEBUGCTL[bit 0] has no meaning.
>> +         * It can be written to 0 or 1, but reads will always return 0.
>> +         */
>
> The comment looks good, please verify it with a test.


OK, I'll add the test into pmu_lbr KUT test together with arch-lbr test 
cases.



>
>> +        if (guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR))
>> +            data &= ~DEBUGCTLMSR_LBR;
>> +
>>           vmcs_write64(GUEST_IA32_DEBUGCTL, data);
>>           if (intel_pmu_lbr_is_enabled(vcpu) && 
>> !to_vmx(vcpu)->lbr_desc.event &&
>>               (data & DEBUGCTLMSR_LBR))