linux-kernel - Re: [PATCH v3 7/9] KVM: x86: Implement Intel Processor Trace MSRs read/write

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Date:   Fri, 1 Dec 2017 09:33:29 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Kang, Luwei" <luwei.kang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>
Subject: Re: [PATCH v3 7/9] KVM: x86: Implement Intel Processor Trace MSRs
 read/write

On 01/12/2017 07:40, Kang, Luwei wrote:
>>> +		case MSR_IA32_RTIT_ADDR0_A ... MSR_IA32_RTIT_ADDR3_B: {
>>> +			u32 eax, ebx, ecx, edx;
>>> +
>>> +			cpuid_count(0x14, 1, &eax, &ebx, &ecx, &edx);
>>
>> Please cache the cpuid_count result, or do the cpuid_count after testing
>> vmx_pt_supported() (which you can use instead of going through kvm_x86_ops).
> 
> Hi Paolo,
>     Thanks for your reply. I have cache EAX in "struct pt_desc" and will initialize in vmx_vcpu_setup().
> +struct pt_desc {
> +       unsigned int addr_num;
> +       struct pt_ctx host;
> +       struct pt_ctx guest;
> +}; 
>     But kvm_init_msr_list() is invoked too early, I have to read from hardware.  So, what about change like this.
> 
> -                       cpuid_count(0x14, 1, &eax, &ebx, &ecx, &edx);
> -                       if (!kvm_x86_ops->pt_supported() || msrs_to_save[i] -
> -                                       MSR_IA32_RTIT_ADDR0_A >= (eax & 0x7))
> +                       if (!kvm_x86_ops->pt_supported())
>                                 continue;
> +                       cpuid_count(0x14, 1, &eax, &ebx, &ecx, &edx);
> +                       if (msrs_to_save[i] -
> +                               MSR_IA32_RTIT_ADDR0_A >= (eax & 0x7))
> +                                       continue;

For kvm_init_msr_list it's okay.  But can you please add a
pt_msr_count() function?

Thanks,

Paolo

> Thanks,
> Luwei Kang
> 
>>
>> Thanks,
>>
>> Paolo
>>
>>> +			if (!kvm_x86_ops->pt_supported() || msrs_to_save[i] -
>>> +					MSR_IA32_RTIT_ADDR0_A >= (eax & 0x7))
>>> +				continue;
>>> +			break;
>