linux-kernel - Re: [PATCH v2 5/8] KVM: x86: Use MTRR macros to define possible MTRR MSR ranges

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Date:   Fri, 12 May 2023 09:35:40 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "guoke@...ontech.com" <guoke@...ontech.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "haiwenyao@...ontech.com" <haiwenyao@...ontech.com>
Subject: Re: [PATCH v2 5/8] KVM: x86: Use MTRR macros to define possible MTRR
 MSR ranges

On Fri, May 12, 2023, Kai Huang wrote:
> On Thu, 2023-05-11 at 16:33 -0700, Sean Christopherson wrote:
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index e7f78fe79b32..8b356c9d8a81 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -3700,8 +3700,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >  			return 1;
> >  		}
> >  		break;
> > -	case 0x200 ... MSR_IA32_MC0_CTL2 - 1:
> > -	case MSR_IA32_MCx_CTL2(KVM_MAX_MCE_BANKS) ... 0x2ff:
> > +	case MSR_IA32_CR_PAT:
> > +	case MTRRphysBase_MSR(0) ... MSR_MTRRfix4K_F8000:
> > +	case MSR_MTRRdefType:
> >  		return kvm_mtrr_set_msr(vcpu, msr, data);
> >  	case MSR_IA32_APICBASE:
> >  		return kvm_set_apic_base(vcpu, msr_info);
> > @@ -4108,9 +4109,10 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >  		msr_info->data = kvm_scale_tsc(rdtsc(), ratio) + offset;
> >  		break;
> >  	}
> > +	case MSR_IA32_CR_PAT:
> >  	case MSR_MTRRcap:
> 
> ... Should we put MSR_IA32_CR_PAT after MSR_MTRRcap so it can be symmetric to
> kvm_set_msr_common()?
> 
> Looks there's no reason to put it before MSR_MTRRcap.

No, it's above MTRRcap for two reasons:

 1. When PAT is moved out of mtrr.c, PAT doesn't get bunded with the other MTRRs
    and so would just need to be hoisted back up.  The end code looks like:

	case MSR_IA32_CR_PAT:
		msr_info->data = vcpu->arch.pat;
		break;
	case MSR_MTRRcap:
	case MTRRphysBase_MSR(0) ... MSR_MTRRfix4K_F8000:
	case MSR_MTRRdefType:
		return kvm_mtrr_get_msr(vcpu, msr_info->index, &msr_info->data);
 
 2. There is no MSR_MTRRcap case statement in kvm_set_msr_common() because it's
    a read-only MSR, i.e. the two can't be symmetric :-)

> > -	case 0x200 ... MSR_IA32_MC0_CTL2 - 1:
> > -	case MSR_IA32_MCx_CTL2(KVM_MAX_MCE_BANKS) ... 0x2ff:
> > +	case MTRRphysBase_MSR(0) ... MSR_MTRRfix4K_F8000:
> > +	case MSR_MTRRdefType:
> >  		return kvm_mtrr_get_msr(vcpu, msr_info->index, &msr_info->data);
> >  	case 0xcd: /* fsb frequency */
> >  		msr_info->data = 3;
> > -- 
> > 2.40.1.606.ga4b1b128d6-goog
> > 
>