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

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Date:   Thu, 30 Nov 2017 13:20:27 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Luwei Kang <luwei.kang@...el.com>, kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, rkrcmar@...hat.com, linux-kernel@...r.kernel.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 27/11/2017 21:24, Luwei Kang 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).

Thanks,

Paolo

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