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 06:40:19 +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;

Thanks,
Luwei Kang

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