Re: [PATCH v10 15/16] KVM: x86: Add Arch LBR data MSR access interface

["Yang, Weijiang" <weijiang.yang@intel.com>]

On 4/28/2022 11:05 PM, Liang, Kan wrote:
>
> On 4/22/2022 3:55 AM, Yang Weijiang wrote:
>> Arch LBR MSRs are xsave-supported, but they're operated as "independent"
>> xsave feature by PMU code, i.e., during thread/process context switch,
>> the MSRs are saved/restored with PMU specific code instead of generic
>> kernel fpu XSAVES/XRSTORS operation.
> During thread/process context switch, Linux perf still uses the
> XSAVES/XRSTORS operation to save/restore the LBR MSRs.

I meant Arch LBR MSRs are switched with perf_event_task_sched_out()/

perf_event_task_sched_in() instead of save_fpregs_to_fpstate()/ 
restore_fpregs_from_fpstate().

sorry for the confusion, will modify it a bit.

>
> Linux perf only manipulates these MSRs only when the xsave feature is
> not supported.
Exactly.
>
> Thanks,
> Kan
>
>> When vcpu guest/host fpu state swap
>> happens, Arch LBR MSRs won't be touched so access them directly.
>>
>> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
>> ---
>>    arch/x86/kvm/vmx/pmu_intel.c | 10 ++++++++++
>>    1 file changed, 10 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
>> index 79eecbffa07b..5f81644c4612 100644
>> --- a/arch/x86/kvm/vmx/pmu_intel.c
>> +++ b/arch/x86/kvm/vmx/pmu_intel.c
>> @@ -431,6 +431,11 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>    	case MSR_ARCH_LBR_CTL:
>>    		msr_info->data = vmcs_read64(GUEST_IA32_LBR_CTL);
>>    		return 0;
>> +	case MSR_ARCH_LBR_FROM_0 ... MSR_ARCH_LBR_FROM_0 + 31:
>> +	case MSR_ARCH_LBR_TO_0 ... MSR_ARCH_LBR_TO_0 + 31:
>> +	case MSR_ARCH_LBR_INFO_0 ... MSR_ARCH_LBR_INFO_0 + 31:
>> +		rdmsrl(msr_info->index, msr_info->data);
>> +		return 0;
>>    	default:
>>    		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
>>    		    (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
>> @@ -512,6 +517,11 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>    		    (data & ARCH_LBR_CTL_LBREN))
>>    			intel_pmu_create_guest_lbr_event(vcpu);
>>    		return 0;
>> +	case MSR_ARCH_LBR_FROM_0 ... MSR_ARCH_LBR_FROM_0 + 31:
>> +	case MSR_ARCH_LBR_TO_0 ... MSR_ARCH_LBR_TO_0 + 31:
>> +	case MSR_ARCH_LBR_INFO_0 ... MSR_ARCH_LBR_INFO_0 + 31:
>> +		wrmsrl(msr_info->index, msr_info->data);
>> +		return 0;
>>    	default:
>>    		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
>>    		    (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {