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

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Date:   Mon, 4 Dec 2017 01:21:20 +0000
From:   "Kang, Luwei" <luwei.kang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.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

> >>> +		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?
>

Of course, I will fix in next version. Thanks!

Luwei Kang

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